MILD FEED RESTRICTION AND COMPENSATORY

GROWTH IN THE BROILER CHICKEN

A Thesis

Presented to

The Faculty of Graduate Studies

of

The University of Guelph

MARIA URDANETA RINCON

In partial fulfilment of requirements

for the degree of

Master of Science

April, 2000

O Maria Urdaneta Rincon, 2000

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ABSTRACT .

MILD FEED RESTRICTION AND COMPENSATORY GROWTH IN THE BROILER CHICKEN

Urdaneta R, Maria University of Guelph, 2000

Advisor: Dr. S. Leeson

The effects of mild feed restriction (MFR) on compensatorj growth and

performance in the broiler chicken was evaluated. MFR was imposed throughout the

productive stage or at early and late growth periods. Qualitative feed restriction was

imposed during the starter, grower or finisher period. Productive parameters and the

occurrence of SDS and ascites were assessed. Apparent nitrogen digestibility and

AMEn were also determined. Broilers subjected to MFR throughout their productive

iife did not compensate at 42 days of age, and they needed more time to attain market

body weight, which reduces the yearly returns compared to ad libitum fed birds.

Imposing qualitative feed restriction reduced market body weight, breast rneat yield,

and mortality at either 42 or 49 d. Birds subjected to an early or late MFR showed

compensatory growth compared to ad libitum fed birds, and no differences were

observed in F:G, mortality, breast meat yield, thigh yield, and AFP at 49 days of age.

Feed restricted birds at an early period however, exhibited a significant improvement

in feed conversion and breast meat yield at 42 d. Apparent nitrogen digestibility was

not affecteci in birds subjected to a MFR at 15 days of age. Diet AMEn was affected in

birds subjected to feed restriction or fed textured diets at 5 days of age, although no

differences were seen at 28 or 48 d.

DEDICATED

TO MY MOTEER CCAUFtA RINCON DE URDANETA" TO MY BROTHER RAFAEL URDANETA" AND TO MY LOVE CCALEXANDER BOSCAN"

ACKNOWLEDGMENTS

1 wish to appreciate aI1 m y gratefully to my adviser Dr. Steve Leeson for

accepting me as a graduate student under his guidance when 1 decided to relocate from

the University of Saskatchewan to the University of Guelph. Thanks Dr. Leeson for al1

your assistance, encouragement, interest, and kindness. 1 also wish to thankfûlly to La

Universidad del Zulia for its economical support on the continuation of my post-

graduate studies. 1 would like to thank other members of my advisory committee,

namely Dr. T. Smith, and Dr. J. Atkinson for their guidance.

1 would also like to express my sincere thanks to the staff of Arkell Poultry

Research Station for al1 their cooperation in the conduction of the experiments.

Gratitude is given to all my graduate fkiends, colleagues and other members of the

Animal and Poultry Science Department who directly or indirectly helped in the

culmination of this degree.

Lastly, 1 would like to express my profoundly gratefully to al1 my family for

giving me the emotional support, the patience, and the perseverance needed for

pursuing my post-graduate studies at the University of Guelph.

THANKS TO EVERY ONE

TABLE OF CONTENTS

1. General Introduction

CEIAPTER II Literature Review 1. Methods of feed restriction 3

1.1 Quantitative feed restriction 3 1.1.1 Physical feed restriction 3 1.1.2 Lighting 4

1.2 Qualitative feed restriction 6 1.2.1 Diet dilution 6 1.2.2 Low-nutrient density diets 7 1.2.3 Feed texture 9 1.2-4 Chemical methods 10

2. Compensatory growth 12 2.1 Factors influencing compensatory growth in the broiler chickens 14

2.1.1 Duration of feed restriction 15 2.1-2 Timing of feed restriction 16 2.1 -3 Severity and nature of feed restriction 17 2.1 -4 Condition of re-alimentation 19 2.1.5 Effect of genetics, sexy and strain 19

3. Rate of development in broiler chickens 21 3.1 Body development and compensatory growth in broilers 22 3.2 Feed restriction and body fat content 24 3.3 Effect of feed restriction on energy metabolism in broiler chickens 26

4. Metabolic disorders related to growth rate 27 4.1 Ascites 28

4.1.1 Effect of feed restriction on the incidence of ascites 29 4.2 Sudden death syndrome 30

4.2.1 Effect of feed restriction on the incidence of sudden death syndrome 31

5. Summary 32 6. General objectives 33

CEZAPTER III

Effect of quantitative and qualitative feed restriction on growth and performance on broiler chickens.

1. Abstract 2. Introduction

3. Materials and methods 4, Results 5. Discussion 6. Conclusion

CHAPTER IV

EEect of early and late quantitative feed restriction on growth and performance in broiler chickens. 58

1. Abstract 2. Introduction 3. Materials and methods 4. Results 5. Discussion 6. Conclusion

Apparent ileal nitrogen digestibility and apparent metabolizabIe energy corrected to zero niîrogen retention determinations Ui broiler chickens fed textured diets and feed restricted at different ages.

1. Abstract 2. Introduction 3. Materials and methods 4. Results S. Discussion 6. Conclusion

CHAPTER VI

General discussion.

REFERENCES

LIST OF TABLES

TABLE

3.1 Percentage diet composition and calculated nutrient analysis, Experiment i

3.2 Percentage diet composition and calculated nutrient analysis, Experiment 2

3.3 Broiler performance in relation to feed restriction, Experiment 1

3.4 Carcass characteristics of broilers at 42 days of age subjected to different levels of feed restriction, Experiment 1

3.5 Income estimation projected to 100,000 broilers subjected to feed Restriction, Experïment 1

3.6 Effect of feed textures on body weight and feed conversion in broilers fed different feed textures, Experirnent 2

3.7 Effect of feed textures on feed intake and rnortality of broiler chickens, Experiment 2

3.8 Carcass characteristics of broilers fed different feed textures, Experiment 2

4.1 Percentage diet composition

4.2 Performance of broiters subjected to feed restriction for varying tirne periods starting at day 5, Experiment 1

4.3 Carcass characteristics of broilers subjected to feed restriction for varying b e penods starting at day 5, Experiment 1

4.4 Performance of broilers subjected to feed restriction for varying tirne penods starting at day 14, Experiment 2

4.5 Carcass charactenstics of broilers subjected to feed restriction for varying t h e periods starting at day 14, Experiment 2

5.1 Percentage diet composition

5.2 Feed intake effect on apparent ileal nitrogen digestibility and AMEn in broilers in broilers of 15 d of age, Experiment 1

5.3 Effects of texture and feed restriction on AMEn (Kcallkg) of starter, grower and finisha diets in broiler chickens, Experiment 2

LIST OF FIGURES

Schematic growth curves of broiler chickens

Broiier growth related to level of feed restriction

Body weight fkom 7 to 21 days

Estimates of time needed to equalize body weight of all treatment groups using 42 d body weight of control birds as a standard

Feed conversion related to days of feed restriction starting at day 5 Experiment I

Total mortality at 49 ci related to feed restriction

Broiler growth curve fiom 7 to 28 days, Experiment 1

Broiler growth cuve from 7 to 28 days, Experiment 2

LIST OF ABREVIATIONS

AFP

AME

AMEn

ANOVA

APP

BW

C

CM

D

F:G

FR

G

GH

H

IGF

KcaI

Kg

Kj

L:D

M

ME

abdominal fat pad

apparent metabolizable energy

apparent metabolizable energy corrected to zero nitrogen

retention

analysis of variance

apparent

body weight

centigrade

centimeter

days

feed conversion

feed restriction

grams

growth factor

hours

insulin-like growth factor

kilocalorie

kilogram

kilojoule

Lighting/darkness

meter

metabolizable energy

Meq

Mcal

MG

MIN

N

NS

NRC

0 2

SAS

SDS

SEM

T m

TMEn

WT

milliequivdent

megacalone

milligram

minutes

nitrogen

not sipnificant

national research council

oxygen

statistical analy sis system

sudden death syndrome

standard error of the mean

tme rnetabolizable energy

true metabolizable energy corrected to zero nitrogen

weight

Improvements in genetics and nutrition of the modem broiler chicken have led

to continuing improvement in feed conversion and carcass yield, which rneans

improved efficiency in productive performance. Improvement in market body weight-

for-age has been achieved due to increased feed intake, which is a consequence of

genetics (Havenstein et al., 1993) as sustained by nutrition and health management.

However such increased growth rate lias caused a greater incidence of

metabolic disorders such as ascites and sudden death syndrome and also skeletal

abnonnalities (Robinson et al., 1992), and increased fat deposition (Yu and Robinson,

1992). These pathologie conditions are closely related to an increased growth rate,

hi& metabolic rate, and increased feed intake.

Generally the growth curve of broiler chickens fed ad Zibiturn follows a

sigmoid forrn (Walker et al., 1995). Birds subjected to a feed restriction program show

reduced growth rate at the beginning of the growth penod when compared to fûll-fed

birds. This decreased growth rate reduces the bird's total maintenance requirements,

which improves feed efficiency when achieving market body weight. If birds attain

market body weight in a shorter time period than normal, feed efficiency will be

irnproved due to a reduction in their maintenance nutrient requirements (Leeson and

Surnmers, 1997).

Feed restriction programs are strategies that c m be used to alter feeding

management in order to decrease to some extent feed consumption and therefore

growth rate, alleviating the occurrence of metabolic disorders and improving feed

efficiency. Research in feed restriction has shown the potential to decrease the

occurrence of ascites (Julian, 1997; Totton et al., 1997), and sudden death syndrome

(Blair et al., 1993; GonzaIes et al., 1998a).

An understanding of the issues c o n c e h g feed restriction is necessary in order

to manipulate the growth rate of broiler chickens while decreasing mortality fiom

metabolic disorders and at the same tirne attaining normal market body weight-for-age

with an improved feed efficiency.

1. METHODS OF FEED RESTRICTION

1.1 Quantitative Feed Restriction

Research has been conducted on the effects of altering feed availability for

both growth and productive performance in broilers (Plavnik and Hurwitz, 1985;

Fattori et al., 1991; Fontana et al., 1992; Deaton, 1995). Results, however, are

contradictory and depend to a great extent oc the timing and severity of the feed

restriction. P hysical feed restriction, lighting programs, and chernical methods are

some of the procedures used to manipulate feed intake.

1.1. f Physical feed restriction

Practical application of physical feed restriction is not straigheonvard due to

the problems of regularly weighing birds, and calculating feed consumption on a daily

basis. Moreover, it is necessary to provide sufficient feeder space in order to prevent

cornpetition arnong restncted birds and to prevent unequal growth of birds within a

flock. Physical feed restriction programs for broilers have been extensively studied

(Yu et al., 1990; Santoso et al., 1993b, Scheideler and Baughrnan, 1993; Zhong et al.,

1995). R e p o ~ s vary according to the age of bird, and level, and length of physical feed

restriction. Deaton (1995) restricted birds to 90, 75, or 60 % of the previous 24-h feed

consumption of W-fed controls fiom 7 to 14 days and showed signifïcant

improvement in feed conversion in restricted birds. In addition, males and females

showed sunilar body weight to control fed birds at 41 days given 90% of control feed

consumption. At the same time, body weight similar to that of controls was achieved

by the restricted chicks at 49 days of age with 60% of feed consumption. These results

are in agreement with those of Scheideler and Baughman (1993), who restricted birds

to 65% of the ad libitum rate fiom 8 to 14 days and showed no significant difference

in body weight at 35 and 45 days of age. In addition, a numerical though not statistical

s i m c a n t improvement in feed conversion was attained in these restricted birds.

Severity of feed restriction, length of restriction, and age at marketing are the

principal factors to take into account in a feed restriction program for broilers.

1.1.2 Lighting

As a normal practice, modem broilers chickens are grown under 23 hrs

Light per day, prirnarily because it is thought that under this light re,gimen feed intake

is greater and therefore growth rate is optirnized. Although lighting programs are not

classified in the literature as a feed restriction method it has been applied. It is known

that by altering Lighting schedules by either reducing the hours of light or developing

intermittent schedules (Wilson et al., 1984) feed utilization is improved plair et al.,

1993; Buys et al., 1998; Apeldoorn et al., 1999). During penods of darkness the

broiler's energy needs for maintenance are lower (Buyse et al., 1996). The incidence

of leg abnormalities is also lowered by reducing the hours of Light each day (Classen

and Riddell, 1989; Renden et al., 199 1) as is mortality and specificdly sudden death

syndrome (Blair et al., 1993; Gordon and Tucker, 1997).

The so called step-dom and step-up lighting programs (Classen and Eddell,

1989) have attained popularity because of reduced incidence of leg abnormalities,

sudden death syndrome and mortality while maintaining the same market weight for

age. Broilers under different reduced lighting programs therefore, will reduce their

feed intake, and so this program can be included within the definition of feed

restriction. However, broilers do leam to eat during darkness when hours of lighting

are low (Morris, 1986). Buyse et al. (1994) studied the effect of intermittent (step-up

and step-down programs) and continuous lighting on the performance of female

broilers. Lower cumulative feed intake and signincantly improved feed conversion

was observed in chickens under an intermittent program (1L:3D fiom 8 to 49 days)

compared with those under a continuous lighting schedule (23 .SL:OSD or 23L: ID). In

addition, compensatory growth was achieved in broilers grown under an intermittent

lighting (step-down and 1L:3D) program to 7 weeks of age. These results are in

agreement with Buyse et al. (1996), who showed improved feed conversion and

compensatory growth in male broiler chickens at 41 days with a light schedule fkom

day 7 of 1L:3D repeated six times daily.

The use of lighting programs has the advmtage of reducing electricity costs,

the incidence of leg abnoxmalities and sudden death syndrome, and of irnproving feed

efficiency with no reduction of weight at market age. Genotype, sex, feeder space, diet

composition and stocking density are the main aspects that can interact with the

lighting program (Buyse et al. 1994), and affect the broiler's final performance.

1.2 Qualitative Feed Restriction

2 Diet dilution

Many workers have used diet dilution as an alternative method of nutrient

restriction because of the advantage of attaining a more consistent growth pattern

within a flock. Diets are mixed with non-digestible ingredients such as fiber, and so

are of reduce nutrient density. Leeson et al- (1991) showed complete compensatory

growth in male and fernale broilers at 42 days of age where growth was lirnited fkom 4

to 11 days due to a diluted diet containing up to 55% of rice hulls as a non-digestible

ingredient. In addition, there was no significant difference in the overall efficiency of

feed utilization, although during the diluted period birds increased their feed

consumption in an attempt to maintain their the energy intake. Jones and Farrell

(1992a) applied diet dilution to broilers by including 60 or 65% of rice hdls to a

c m b l e starter diet fiom 4 to '7 days of age, showing complete compensatory growth

at 48 days of age. These results are in agreement with those of Zubair and Leeson

(1994a), who reported no difference in.body weight at either 42 or 49 days when birds

were fed a 50% oat-hull diluted diet for six days. In another trial, Leeson et al. (1992)

offered birds a conventional finisher diet diluted up to 50% with a 5050 mixture of

sand:oat hulls fiom 35 to 49 days of age, and showed no significant difference in body

weight at 49 days or breast weight at 42 or 49 days of age.

The use of diluted diets relies upon the fact that broiler chickens eat close to

their physical intake capacity (Newcombe and Summers, 1984). Leeson et al. (1992)

reported somewhat unexpected growth and feed intake with diet dilution during the

finisher period. This might have occurred because broiIers obtained energy from

supposedly non-digestible ingredients (Leeson et al. 1992) or that the oat hull dilution

improved the nutrient availability (Leeson and Zubair, 1997), such that birds acquired

more energy than anticipated for growth. Moreover, Leeson et al. (1992) reported that

broilers during the nnisher period altered their feed intake according to the energy

density of the diet. These results are in agreement with those of Zubair and Leeson

(1994a), where birds receiving a 50% oat hull-diluted diet increased their feed intake.

This trend to increased feed intake when feeding a diluted diet seems to be the bird's

attempt to maintain its nutrient intake, and suggests that modem broilers do, in fact,

adjust intake in response to variable diet nutrient density. These findings are at

variance with the previously described report of Newcombe and Summers (1 9 84).

1.2.2 Low-nutrient density diets

The use of low protein or low energy diets is another means of achieving

reduced growth rate. This method has an advantage in that it does not require any

additional labor of weighing the feed, and is accomplished by lowering the level of

either protein or energy. For optimum growth broilers are given 23%, 20%, and 18%

of crude protein in the starter, grower, and finisher periods respectively, and 3200 kcal

MEkg diet (NRC, 1994). When broilers are fed with low nutrient dense diets they will

increase their feed intake in an attempt to maintain nuîrient intake (Leeson and

Summers, 1997). Plavnik and Hurwitz (1 990) showed that broilers fed ad libitzirn with

a 9% crude protein diet fiom 8 to 14 days markedly reduced their feed intake and

weight gain by about 63% and 88% respectively. This reduction in feed intake may

have been due to an imposition of a proteidamino acid deficiency, since other

nutrients were at normal levels. In addition, low protein, feed-restrkted birds could not

cornpensate for this early retardation and body weight was less compared to controls at

56 days of age; bowever, there was improved feed efficiency.

Rosebrough and McMurtry (1993) showed the effect of 6 days of d i e t q

energy restriction in broiler chickens- The restriction period was fiom 6 to 12 days and

was designed to only support the maintenance requirements for body weight. Body

weight at 54 days was achieved for birds given feed ad libitum fi-orn day 13 to 54, and

for those fed ad libitum from 21 days onward. Feed efficiency was not significantly

different between restricted and unrestricted birds. Meluzzi et al. (1995) utilized a

"hi@ density" diet (23-24% protein, 3.1-3.2 Mcal MEkg) and a low density diet

(19% protein and 2.9 Mcal ME/kg). They showed that birds receiving the low density

diet were smaller than the birds fed the hi& density diet at both 42 and 49 days of age.

This reduced weight gain was due to a lower feed intake. Leeson and Summers (1997)

utilized finisher diets varying in energy level from 2700 to 3300 kcal MEkg and

showed no significant difference in body weight at 49 days. There was increased feed

intake by birds fed the lower energy level diets.

Feeding broilers with combinations of high density diets (21 -2-25.9% protein,

13.9-14.3 MJ ME/kg) produces greater live bird performance and carcass meat

components until 50 days of age, but the rate of gain was Iower when compared with

combinations of low-high density diets (1 9.1-22.5% protein, 12.7-1 3.1 MJ MEkg),

(Walker et al., 1995).

Growth depression observed in birds fed lower density diets could be

overcome with an increased feed intake and longer length of time to attain the

desirable body weight- However, longer time of feed restriction, accounted for more

than 8 days, and lower diet density where the ratio of protein and energy content is

decreased, the birds' ability to compensate normal body weight for age is diminished.

1.2.3 Feed textures

Feed particle size also influences broiler growth and development (Reece et al.,

1985, Havenstein et ai., 1994, Jones et al., 1995). Broilers fed crumble-pellet diets

show improved weight gain, feed intake, and feed conversion compared to birds fed

mash (Calet, 1965). In addition, the use of mash feed at different stages of the broiler's

growth may be employed as a method of limiting feed intake. Birds offered mash

spend more tirne consuming their feed compare to birds fed pellets (Jensen et al.,

1962, Savory, 1974), and therefore, expend more energy in this process. Any

improvement in growth rate due to eatïng pellets might be due to some extent to the

increased bulk density of pellets (Andrews, 199 l), which increases nutrient intake in

some situations.

Nir et al. (1 995) fed male and female broilers to 49 days with mash or c m b l e

diets during the starter and grower perïods, and mash or pellets for the nnisher period.

Males showed a significant increase in body weight and improved feed conversion

when fed pelleted compared to mash diets. On the other hand, the improvement in

performance was not evident for femaies, which showed no significant difference

either in body weight or feed conversion at 49 days of age. Mortality was higher in

birds fed pelleted diets. These results are in agreement with those of Jones et al. (1995)

and Hamilton and Proudfoot (1995) where an improved weight gain and feed

conversion at 6 weeks of age were obtained in birds fed pelleted compared to mash

diets. The improvement in broiler performance with pelleted diets may be attributable

to a greater digestibility of carbohydrates together with increased daily nutrient intake

(Hamilton and Proudfoot, 1995), better nutrient availability (Nir et al., 19951, andor

less feed wastage (Calet, 1965, Savory, 1974)- Because chicks fed pelleted diets

spend less time and energy feeding, they were less active than mash-fed birds (Nir et

al., 1994), and so spend less energy for maintenance. The increased mortaiity due to

altered feed texture might be linked to a reduced activity (Nir et al:, 1995).

1.2.4 Chemical methods

Another method that has been used to depress the feed intake of broilers is the

use of chernicals or phamacological agents. Pînchasov and Jensen (1989) used 1.5 or

3% glycolic acid as an anorectic agent fiom 7 to 14 days in order to supress the feed

intake of chicks. Feed intake was severely reduced, resulting in 22% and 50% weight

reduction with 1.5% or 3.0% glycolic acid inclusion respectively. Body weight of

these chernically restricted male broilers was not significantly different at 49 d fiom

those fed ad libitum. Oyawoye and Krueger (1990) utilized phenylpropanolamine

hydrochloride and monensin sodium as appetite suppressants. Phenylpropanolamine is

known as an anorectic dmg (Silverstone and Kyriakides, 1 98Z), and monensin sodium

is an ionophore which at low concentrations acts as a cocciodiostat, but at higher doses

produces an anorexic effect in birds (Cervantes and Jensen, 1984). Oyawoye and

Krueger (1986, 1990) showed that with the inclusion of 400 and 300 mgkg of

phenylpropanolamine hydrochionde and monensin sodium respectively in the diet,

body weight of birds was signiticantly decreased at 4 weeks of age, with this effect

being due to a significant reduction in feed consumption. However, the use of

phenylpropanolamine to reduce feed intake in broiler breeders is not appropriate

because of tolerance developed to the dmg by older broilers (Oyawoye and Krueger,

1990). Pinchasov et al. (1993) ùicorporated 3% propionic acid in the diet as an

anorectic agent. Reduction in feed intake was achieved, but this depression in feed

consumption was lower than that obtained when using physical feed restriction, This

effect might be due to an adaptation to the propionic acid by the birds when used for a

long penod (Oyawoye and Kreuger, t990). In addition, Pinchasov and Elmaliah

(1994) showed that 1 or 3% of acetic and propionic acids included in the diet act as

appetite suppressors, and so decrease body weight gain in broilers. Savory et al.

(1996) used 50g/kg of calcium propionate as an appetite suppressor and found that

weight gains of chemically restricted birds were close to those obtaining under a

recommended program of quantitative feed restriction for female broiler breeders

between 2 to 6 weeks of age. Decuypere et al. (1996) showed that jojoba meal can be

used in the diet of broiler breeders in order to reduce their feed consurnption, and that

this effect is due to the presence of a substance called simmondsin which appears to be

an anorexic agent.

This qualitative method of feed restriction has the benefit of evenly distributhg

the feed among birds, and so reducing the variation in growth that can occur with

physical feed restriction programs.

Quantitative and qualitative feed restriction are procedures that cm be applied

to manipulate the feeding strategies of poultry in order to decrease growth, and

metabolic rate to some extent and so alleviate the incidence of some metabolic

diseases as well as irnproving feed conversion in broiler chickens.

2. COMPENSATORY GROWTH

The maximum growth rate of an animal is genetically predetermined and each

animal follows a conventional growth c w e when conditions are favorable. If birds

attain market body weight in a shorter time penod, feed efficiency will be improved

due to a decrease in their maintenance requirements (Leeson and Summers, 1997). For

this reason, there is current interest in the use of feed restriction programs to modiQ

the bird's pattern of growth, so decreasing their maintenance needs. Compensatory

growth refers to the accelerated growth noted in animals of the same age and breed

that were previously feed-restricted (Wilson and Osbourn, 1960; Ryan, 1990). In

poultry production this concept has been studied for about the last 10 years.

UsuaIly the growth curve of broilers chickens fed ad libitum progresses as

shown far lines A to B (Figure l), although this is an oversimplification, since birds

do not grow at an even rate (Leeson and Summers, 1997). As aoted in Figure 1, birds

under a feed restriction regimen (C) have a slower growth rate at the beginning of the

growth period compared to ad libitum fed chicks (A,B). This reduced growth rate

decreases the bird's overail maintenance requirements, and if achieving growth

compensation feed efficiency is improved.

CompIete compensatory growth and improved feed efficiency in broiler chickens

under early feed restriction prograrns has been recorded by flavnik and Hunvitz

(1990), Santoso et al. (1993b), Ziibair and Leeson (1994a), and Deaton (1995).

Figure. 1. Schematic growth curves of broiler chickens

Leesoa and Summers ( 1 997)

However, other workers have failed to obtain compensatory growth in broiler chickens

under similar nutritional conditions (Fontana et al., 1.992; Ramlah et al., 1996;

Cristofori et al., 1997). Birds exhibiting such reduced growth during a restriction

period have reduced plasma concentrations of insulin-like growth factors (IGF-1 and

II), (Leili et al., 1997), which rnay explain this lower growth. When normal feed

availability is restored, chicks grow at a higher rate than normal in order to attain

normal weight for age. This accelerated growth observed when the feed restriction

period is terminated may be due to a higher level of growth hormone (GH)

concentration observed in previously feed-restricted birds (Buyse et al., 1997).

Compensatory gmwth can be accomplished when birds divert more energy

towards growth and/or if the existing energy is utilized in a different rnanner (Ryan,

1990). The mechanisms involved in the process of growth compensation seem to be

related to a reduced maintenance requirement, an increased food intake relative to

body size, alteration in the proportion of fat and protein deposited in the tissues, and/or

irnproved feed efficiency for growth (Ryan, 1990; Rowan et al., 1996). In addition, the

energy that sustains the accelerated growth rnay corne f?om a reduction in the overall

maintenance energy needs (Yu and Robinson, 1992), andor to a decrease in the basal

rnetabolic rate noted in feed-restricted birds (Zubair and Leeson, 1994b). Another

advantage in reducing early growth in broiler chickens is reduced mortality caused by

rnetabolic disorders.

2.1 Factors influencing compensatory growth in the broder chicken

The response of broiler chickens to growth compensation following a period of

feed restriction may Vary due to factors such as duration, timing, and severity of feed

restriction, condition of re-alimentation, and the effects of sex and strain. These factors

have been previously reviewed by Wilson and Osboum (1960), Yu and Robinson

(1992) and Zubair and Leeson (1996b).

2.1.1 Duration of feed restriction

It is generally recognized that with an extended period of feed restriction it is

more difficult for broilers to achieve complete growth compensation and so attain

normal market body weight for age. Washbum (1990), Jones and Farrell (1992a),

Santoso et al. (1993a), and R o t . et ai. (1993) have aIl shown this effect with longer

penods of feed restriction. Compensatory growth has been achieved by broilers under

short penods of undemutrition @alIay et al., 1992; Santoso et al., 1993a; Deaton,

1995). However, other workers failed to attain compensatory growth in broiler

chickens that were feed-restricted during a simiIar penod (Yu et al., 1990; Fontana et

al., 1992; Palo et al., 1995). Santoso et ai. (1993a) feed-restricted broilers for a penod

of 10 days (day 7 to day 17) allowing different times of fkee access to feed, and

reported that body weight of feed-restricted chicks was significantly lower than those

of od libitum birds at market age. Robinson et al. (1992) feed-restricted chicks for 7

days using either a skip-a-day program or daily limited restriction and reported that

birds on the skip-a-day program showed lower weight gain than the birds restricted

each day. However, Jones and Farrell (1 9Wa) cornpared discontinuous and continuous

food restrictions beginning at day 7 and showed that body weight was not signincantly

different compared to ad libitum fed birds. Cristofori et ai. (1997) fed broilers under a

skip-day program (one day fast and one day fed ad libitum) fkom 7 to 28 days of age,

and showed that resûicted birds did not compensate in final body weight at both 42 or

49 days. It appears that the method and duration of feed restriction applied has

different effects

application of a

on the response of broilers. A

short feed restriction program

practical beneficid effect on the

is improved feed efficiency and

associated reduction in production costs, as long as the time to reach market weight is

not compromised.

2.1.2 Timing of feed restriction

Time of imposing a feed restriction program is of major importance because

the later that bùds are feed-restricted the less the opporhmity to achieve desirable

productive performance. Benyi and Habi (1998) feed-restncted birds nom 4 to 8

weeks of age and showed that feed-restricted treatment birds were not able to achieve

normal final body weight at 56 d. Restricting broiler chickens to a level that only

supports their maintenance requirements fiom 7 to 21 or 21 to 35 days resulted in

lower body weight at both 42 and 49 d, compared to ad libitum fed chicks (Cristofori

et al., 1997). The lack of recovery in body weight for the restricted birds compared to

ad libitum fed birds may be related to the duration of, and age at initiation of, the

restriction period. Some workers suggest that the most favorable hme to apply a feed

restriction program is during the second week, rather than Iater (Robinson et al.,

1992). Plavnik and Hurwitz (1988) suggest that feed restriction programs rnay start at

6 days of age, and continue no Longer than 7 days in order to allow birds to attain

growth compensation by 49 days. Feed restriction programs beginning at an earlier

age rather than later seem to be more beneficial to achieving the objectives on the

performance response of broiler chickens.

2.1.3 Severity and nature of feed restriction

Energy reduction, feed withdrawal, and diet dilution are the most cornmon

techniques of nutrient restriction. Restricted birds can be fed above or at energy

maintenance needs. It is generdly known that the growth response of broilers d e r re-

feeding is related to the seventy of pnor restriction but the more severe the restriction,

the less the opporhinity to recover at a given market age. In general, the degree of

energy restriction is based on supporhng only the maintenance requirement, rather

than allowing for growth. Plavnik and H M t z (1985, 1988) suggested a calculated

value of 1.5 kcal ME/day/g B W ~ to sustain maintenance energy requirernents for

male broiler chickens. Using this energy value, birds in fact gain some weight, hence it

is suggested that broilers under a feed restriction prograrn may have slightly lower

maintenance requirement. Reduction in energy requirements rnay be due to a decrease

in the basal metabolic rate noted in feed-restricted birds (Zubair and Leeson, 1994b). It

is not known if the recovery of body weight achieved in some restricted chicks is due

to changes in the bird's energy balance or due to variations in body water retention

(Rosebrough and McMurtry, 1993). Fontana et al. (1992) restricted male chicks by

providing 40 kcal ME bird/day. The restriction period lasted 6 or 7 days and began at

4 days of age, and broiler chickens under restriction were unable to normalize weight -

gain, and had a significantly lower body weight at 49 days. These results are in

agreement with other workers who were unable to obtain compensatory growth by

broilers subjected to sirnilar degrees of feed restriction (Yu et al., 1990; Robinson et

al., 1992; Rosebrough and McMurtry, 1993; Palo et al., 1995). In an attempt to

elucidate the nature of different growth responses of broilers subjected to similar

patterns of restriction, Summers et al. (1990) and Fontana et al. (1992) suggested that

the broilers used by Plavnik and Hurwitz (1985, 1989; Plavnik et al., 1986) were of

lower genetic potential than those used in North Amenca which could influence theu

ability to compensate fully following feed restriction.

Zubair and Leeson (1994a) diluted a conventional broiler starter diet with 50%

oat hulls and fed broiler chickens for 6 days, either with a continuous or discontinuous

daily schedule. Growth compensation occurred in all restricted birds by 35 days of age

and no significant difference in overall feed eficiency was observed. It was noticed

that birds fed a diluted diet increased their feed intake in an attempt to maintain their

nutrient intake (Leeson et al., 1991). Moreover, giving birds the diluted diet in a

discontinuous program improved their ability to adjust and increase their feed

consumption (Zubair and Leeson, 1994a).

Santoso et al. (1993b) fed broilers with a commercial starter diet to 21 days of

age. At 7 days of age birds were feed-restricted to 75, 65, 55, or 45% of ad libitum

intake for 10 days (day 7 to day 17). Body weight of severely restricted (65% and

under) male and female broiler chickens was significantly lower than ad libitum fed

birds at 42 days, but a complete growth compensation was attaio at 49 days. Feed

eficiency was improved in restricted compared to ad libitum fed birds. Such improved

feed utilization might occur due to reduced maintenance requirements during the

period of restriction and because birds search in the litter for feed and so reduce feed

wastage. These results are in agreement with Deaton (1995), who showed Iower body

weight at 41 days of age in restricted birds dlowed 75% and 60% of ad libitum intake.

The response of broiler chickens to a feed restriction program depends on the severity

18

and length of the restriction period. It seems that the more severe and the longer the

duration of a feed restriction program, the less the ability of birds to attain the

expected market weight for age.

2.1.4 Condition of re-alimentation

It has been suggested that the level of nutrients used in the realimentation diets

may have an effect on broiler growth. Fontana et al. (1992) suggested that protein

might be a limiting nutrient in the recovery of restricted birds. However, PlaMik and

Hurwitz (1989) showed that higher levels of dietary protein used during re-feeding did

not alter body weight or feed efficiency at the end of the trial. These results are in

accord with Santoso et al. (1995) and Leeson and Zubair (1997), who suggested that

dietary protein level following restriction had no meaningful effect on growth rate or

feed efficiency, and that increasing the lysine leveZs during re-feeding actually

decreased growth rate in previously restricted birds. There does not appear to be any

advantage on the final gmwth response of broilers to re-feeding with higher levels of

dietary protein or amino acids than used normally for that age of bird.

2.1.5 Effect of genetics and sex

The response of broiler chickens to a period of undernutrition will depend on

the genetics and sex of bird used. Gous et al. (1999) suggested that genetic potential

influences broiler growth response because it affects their nutritiond requirements.

Havenstein et al. (1993) pointed out that genetic potential rather than nutrition has a

greater effect on broiler body composition. It appears that any response observed in

chicks subjected to an under-nutrition regimen is linked to some extent to the effect of

genetics.

Thus it is not surprising that discrepancies in the resdts concerning the

response of broiler chickens subjected to under-nutrition programs has been credited

to differences in genetics of birds used (Yu and Robinson, 1992; Fontana et al., 1992;

Scheideler and Baughman, 1993). However, other workers have not shown differenczs

among strains to compensate body weight and reduce fat deposition (Jones and Farrell,

1992a; Plavnik and Hurwitz, 1992; PlaMik and Balnave, 1992). In addition, Jones and

Farrell (1992a) have established differences in energy maintenance requirements

among strains used in Australia and those used in Israel by Plavnik and Hurwitz

(1985, 1988). Jones and Farrell (1992a) suggested that 1.5 kcal/day/g B W ~ ~ as

suggested by PlaMik and Hurwitz (1985, 1988) to support maintenance needs was an

overestimate for modem strains of birds used in Australia. When implementing a feed

restriction program, the maintenance requirements of the strains used should be

known, because this could be a factor that influences the success or lack of the

realimentation program.

Generally male broiler chickens have a greater growth rate and leaner body

composition than do female broilers. Male broilers also have a superior capacity to

display growth compensation than do females (Plavnik and Hurwitz, 1991; Santoso et

al., 1993ab), although Deaton (1995) showed that both male and female broilers

attained complete compensatory growth at 41 days following just 10% restriction (day

7 to day 14) relative to ad libitum daily intake.

3. RATE OF DEVELOPMENT IN BROILER CHICKENS

It is knovm that nutritional and environmental conditions have an effect on

growth rate. Walker et al. (2995) pointed out that using different nutritional p r o p m s

produces variation in the rate of body weight gain as well as variation in carcass

composition of broilers. It is accepted generaily that the growth rate cuve of broiler

chickens follows a sigmoid shape, and that during the first 2 weeks post-hatch is the

time that the main variation in growth rate and feed intake takes place (Marks, 1979).

Moreover, greater improvement in body weight has been achieved by genetic selection

(Marks, 1979) than by nutrition programs (Havenstein et al., 1993). It is usudly

assumed that the more feed that birds consume, the greater the body weight at market

age. Pym and Nicholls (1979) suggested that about 70% to 90% of the increased

growth seen in broilers has been due to hcreased rates of feed intake. Studies have

been done in order to understand the relation between feed consumption and genetics.

Barbato (1994) stated that the controZ mechanisms of feed intake post-hatch are related

to genetic selection for body weight, and suggested that catecholamine levels are

linked to the level of feed consurnption d e r hatch. Pasternak and Shalev (1983)

proposed that feed intake depends on the growth rate and on the shape of the growth

curve. In addition, improvement noted in body weight of birds due to genetic selection

has been highly correlated with feed consumption rather with the association between

body weight and feed efficiency (O'Sullivan et al., 1992). Improvements in feed

processing have improved quality of feed, hence improving digestibility of the feed

consumed and dlowing better expression of growth potentials.

IlifFerences among genotypes, such as mature body size and mature

composition might ifluence the broiler's capacity for growth because these

parameters &ect their feed intake and nutritional requirements for an optimum

performance (Gous et al., 1999). Accelerated weight gain due to genetic selection is

also related to changes in the villus surface area, which improves digestion and

absorption of nutrients and hence increases the feed intake (Smith et al., 1990). An

understanding of the differences among different broiler strains affecthg their growth

potential during ad libitum feeding might supply important information for feed

restriction strategies (Knketova et al., 199 2).

The improvement in body weight observed in modem broiler chickens is

linked to greater intake and the improved nutritional value of feed. Differences shown

in broiler performance among different strains are due to an uneven potential for

growth which affect their feed consurnption and nutritional needs.

3.1 Body development and compensatory growth in broilers

In some countries, poultry consumers are demanding rnainly breast meat

(white meat); therefore, researchers should consider this fact when using any feed

restriction method due to the inconsistent data concerning potential growth of different

carcass cornponents. Research has been done to elucidate the endocrine mechanisms

involved in compensatory growth. During restriction penods the plasma concentration

of insulin-like growth factors (IGF-1 and II) decrease, and this reduction is related to

the degree of feed restriction (Leili et al., 1997). Buyse et al. (1997) suggested that

broiler chickens exhibiting an accelerated growth d e r a restriction period have greater

growth hormone (GH) concentrations than do non-restricted birds, and so improved

protein deposition occurs. In feed-restricted birds the quantity of feed intake during the

repletion stage might also controi de novo Iipogenesis (Rosebrough and McMurtry,

1993).

The effect of feed restriction programs on growth of carcass components has

been studied. Susbilla et al. (1994) found that broilers restricted to 50% of ad libitum

intake fiom 5 to 1 1 days had a greater growth rate fiom 12 to 39 days of age than did

the control group, though no significant differences in breast and thigh meat yield

were shown between restricted and unrestricted birds. These results are in agreement

with Scheideler and Baughman (1993) and Zubair and Leeson (1994a). Walker et al.

(1995) suggested that giving broilers high density diets improved live weight gain and

reduced the amount of carcass fat. Gous et al. (1999) pointed out an allometric

relationship between breast meat and whole body weight. It seems that the relative

growth of the breast occurs proportionaily to the Iive weight gain. In these studies, the

growth of breast muscle differed statistically among strains, but no significant

difference was reported in the proportion of breast muscle relative to live weight

between male and fernale broilers (Acar et al., 1993). It seems that genetic potential,

accounts for some 80-85% of broiler meat yield (Havenstein et ai., 1993). Palo et al.

(1995) restricted broiler chickens to an energy intake of 1.5 kcal ME/d/g BW 67 firom 7

to 14 days of age, then refed birds ad libitum, and showed that breast meat yield and

body weight of restricted birds were significantly reduced,

Data concerning growth of breast meat in birds subjected to feed restriction is

inconsistent, and a better understanding of how duration and severity of feed

restriction affects it is of simiificant importance.

3.2 Feed restriction and body fat content

In order to produce Ieaner meat and lessen the unfavorable effects of fat on

human health there is interest in the poultry industry in reducing fat deposition in

broiler carcasses, Rosebrough and McMurtry (1993) suggested that an under-nutrition

and re-feeding regimen produced an increase in totd body fat. However most results

obtained with feed restriction progarns intended to diminish the carcass fat content in

broiler chickens have been inconsistent. This inconsistency rnay be due to the different

strategies of feed restriction applied, conditions of re-alimentation, age of imposition,

strain of bird and sex, al1 of which may affect the bird's response. Reduction in

abdominal fat content due to the application of a feed restriction regimen was achieved

by some workers (Plavnik and Hurwitz, 1985; t 988; 199 1 ; Pa10 et al., 1995; Jones and

Farrell, 1992qb; Santoso et al., 1995). However, this desirable response has not been

shown by other workers (Summers et al,, 1990; Yu et al., 1990; Santoso et al., 1993b;

Fontana et al., 1993; Sheideler and Baughman, 1993; Deaton, 1995; Ramlah et al.,

1996).

The activity of the enzymes associated with hepatic lipogenesis, namely fatty

acid synthetase, isocitrate dehydrogenase, and malic enzyme, are depressed during the

nutrient restriction period, but after re-feeding their activity is increased (Rosebrough

et al., 1986; McMurtry et al., 1988). Rosebrough and McMurtry (1993) suggested that

d e r a short period of feed restriction broiler chickens exhibited an increase in de novo

lipogenesis, which was related to the quantity of feed given. In commercial broiler

chickens adipocyte hyperplasia in the abdominal fat pad occurs mainly d u h g the first

week of age, but it can be noted until 15 weeks of age (Hood, 1982). Zubair and

Leeson (1996a) reported that feed-restricted broiler chickens had the same percentage

of fat content as did an ad libitum group. This is mainly due to hypertrophy of the fat

cells rather than hyperplasia Zhong et al (1995) feed-restncted broiler chickens fiom

7 to 12 days of age and showed no difference in the adipocyte numbers fiom the

abdominal fat pads at either 28 or 42 days of age for restricted and ad libitum birds.

However, these workers did observe a reduction in the adipocyte volume for restricted

birds. Jones and Farrell (1992b) have suggested that the reduction in body fat content

observed in broiler chickens under feed restriction is due to a temporary delay in fat

deposition. The rate of iipogenesis for feed-restricted broiler chickens is lower than for

those fed ad libitum at 54 days (JXosebrough and McMurtry, 1993; Zhong et al., 1995).

In addition, this lower rate of lipid synthesis observed in restricted-refed broilers could

be a possible reason for reduced fat content at 7 or 8 weeks of age when an under-

nutrition program has been applied. .

The application of feed restriction prograrns that allow complete recovery of

body weight as well as a leaner body is of econornic importance. A better knowledge

and understanding of how age of initiation, strain of bird, method of feed restriction,

severity, and duration of under-nutrition could reduce the body fat content while

maintainhg meat yidd is of economic interest.

3.3 Effect of feed restriction on energy metabolism in broiler chickens

Hunivitz et al. (1980) suggested that in order to produce a gain in lean body

mass, the body expends about 0.5 to 0.7 kcal ME/g gain. It is hypothesized that

energy and other nutrients needed to maintain compensato~ gowth corne fiom a

reduction in the maintenance requirements of the under-fed animal, because they have

a reduced body size after the re-feeding period (Wilson and Osbourn, 1960,

OYDonovan, 1984, Rowan et al., 1996), andlor because they have a reduced basal

metabolic rate (Zubair and Leeson, 1994b). It is generally known that birds use diet

energy for maintenance, activity, heat production, or storage as lem body tissue (Scott

et al, 1982), and that the excess is stored as fat. Differences in energy intake and

energy expenditure may not be the only reasons for differences in body fat content.

For exarnple, differences could result due to a variation in the proportion of fat and

protein deposition in the tissues (McLean and Tobin, 1988, Rowan et al., 1996).

There is some concern about the potential effect of feed restriction on diet

apparent metabolizable energy correcteci to zero nitrogen retention (AMEn). Some

workers have suggested that the level of feed intake does not affect the AMEn value of

a diet (Hill and Anderson, 1958; Bourdillon et al., 1990), while others have reported

that diet AMEn value is affected (Sibbald, 1975; Guillaume and Summers, 1970;

Sibbald and Wolynetz, 1985). It seems to be that both fecal and urinary energy losses

depend on the amount of feed consumed, thus affecting AMEn values. It is generally

accepted that feed intake levels affect the AME values via an influence on endogenous

losses. With high levels of feed intake, the energy voided in the excreta is less

influenced by endogenous losses. Sibbald (1976) suggested the use of tnie

rnetabolizable energy (TME) to reduce this effect. Endogenous energy losses are

excreta components containing mainly nitrogen, hence correcthg ME values to zero-

nitrogen retention reduces this variance (Sibbald and Morse, 1982). Studies done by

Kussaibati et al. (1982) reported that the level of feed intake did not influence the

AMEn of diets containing 50 g lipids/kg, but those of other diets containing 150 g

lipidskg were affected by level of feed consumption-

Jones and Farrell (1992b) resîricted broiler chickens to 3.1 kJ AME/g W /d

fiom 7 to 14 days of age, and showed that the AME of the diet was significantly

reduced, compared to ad libitum fed birds. Nevertheless, these differences were not

observed after the re-feeding period, suggesting that feed restriction does not have a

prolonged effect on the metabolizable energy of the diet. Zelenka (1997) evaluated

AMEn in broiler chickens using different levels of intake, and reported that AMEn

was reduced when feed consumption was increased, and these lower values were Que

to a variation in ad libitum intake. Flores and Castanon (1991) reported that the

TMEn values of some ingredients were not significantly affected when at least 50

gram of the diet was offered, although lower feed amounts did influence these vaIues.

However, Sibbald and Morse (1982) suggested that values of TMEn were independent

of the amount of feed intake and that T M . values for unfed birds decreased only

slightly as feed intake increased.

4. METABOLIC DISORDERS RELATED TO GROWTH RATE

The two main metabolic disorders affecting today's broiler chickens are ascites

and sudden death syndrome. These pathologie conditions are closely related to an

increased growth rate, hi& metabolic rate, and increased feed intake. Moreover, the

use of high density diets to achieve the broiler's genetic potential has improved the

growth rate, and concornitantly increased the incidence of these disorders.

Studies aimed at limiting feed intake may therefore be also beneficial in

limiting such morbidity mortality in broilers. Following is a discussion of these major

disorders, related to the significance of limiting feed intake as a control system.

4.1 Ascites

In the modem broiler industry economic losses due to ascites are a major

problem world wide. In Canada, condemnation of broilers due to ascites is of major

concem because it accounted for approximately from 3.5 % of total condemnations for

1986 to 19% for 1994 (Olkowski et al., 1996). Ascites was first observed in birds

reared at hi& dtitudes, but it is now known to occur in birds under cold stress at any

altitude. As a result of these observations, the significance of hypoxia in its aetiology

has been studied. Any condition causing hypoxia, even at sea leveI, may provoke the

occurrence of this metabolic disorder. It is suggested that any factor that increases the

0 2 requirernents, blood viscosity, and number of red blood cells, and reduces the rate

of 0 2 transfer in h g s or the 0 2 canying capacity of the blood may predispose to the

incidence of ascites (Julian, 1997). Ascites relates to the abnormal accumulation of

fluid in the abdominal cavity, which c m result fiom several physiological changes.

The pathologic process of ascites is very cornplex, and is primarily focused on

hypoxia, which is greatly intensified due to an imbalance between the growth

requirements and the capacity of the cardiovascular and pulmonary system to meet the

body needs- The pathogenesis involves a pulmonary hypertension, right ventncular

hypertrophy, valvular ùisuficiency, increased venous pressure, and hepatocellular

damage (Julian, 1993; Beker et al., 1995; Okowski et al., 1998). Other factors such as

disease, genetics, nutritional regirnens, toxins, environmental conditions, and

management practices may predispose or even directly promote the incidence of

ascites in birds.

4.1.1 Effect of feed restriction on the incidence of ascites

The implementation of feed restriction as a management technique to reduce

the occurrence of ascites in broilers has been studied (Arce et al., 1992). Julian (1997)

reported that limiting feed intake reduces or may prevent the incidence of ascites. The

feasibility of this program relates to monetary retwns- Gonzales et al. (1998a)

restricted broiler chickens to 20% of ad libitum intake fiom 8 to 21 days of age, and

showed that mortality was reduced by 20% in feed-restricted birds. Moreover, ad

libitum fed birds showed an increased incidence of right cardiac hypertrophy at an

earlier age than did feed- restricted birds. Tottori et al. (1997) restricted the time of

feed consurnption of broiler chickens to 12 houdday fiom 15 to 35 days of age, and

reported a significant reduction in the occurrence of ascites in feed-restricted

compared to ad libitum fed birds. Arce et al. (1992) subjected broiler chickens to feed

restriction at high altitude, and showed that feed-restricted birds had significantly

lower mortality due to ascites. The lower mortality due to ascites in feed-restricted

broilers seems to be because of a reduction in growth rate, and so oxygen requirements

are less. Fedde et al. (1998) reported that broilers under feed restriction showed

superior pulmonary ventilation, which might reduce the occurrence of right ventricdar

heart fdure. The benefits fÎom reducing the incidence of ascites in birds undergoing

feed restriction may also be attained with the implementation of lighting programs

because the oxygen requirements will also be reduced (Gordon, 1997). The

implementation of a short-term feed restriction program, such as from 7 to 16 ages of

day, did not reduce the prevalence of ascites in feed-restricted compared to ad libitum

fed birds (McGovem et al., 1997). The lack of reduction in the incidence of ascites

seems to be related to too short a penod of under-nutrition. It appears that in order to

decrease the prevalence of ascites, more severe and longer periods of under-nutrition

are required.

4.2 Sudden Death Syndrome

Sudden death syndrome (SDS), also known as "flip-over", is a metabolic

disorder occurring mainly in fast growing chicks and with a higher prevalence in male

than female broiler chickens. Birds fond dead are commonly lying on their back with

their feet upwards and the neck extended with no evidence of any disease. The

pathogenesis of SDS is related to a lethal cardiac collapse (Olkowski and Classen,

1997). Squires and Suwners (1993) suggested that both SDS and ascites in broilers

are the consequence of the same metabolic condition, with SDS being the acute

manifestation of the disorder, seerning to occur at a young age, while ascites is the

presentation of the chronic phase, and is generally observed in older birds. Factors

such as nutritional status, environmental condition, and diet ingredients are not easily

correlated with predisposition to 'the incidence of SDS (Leeson et al., 1995). Dietary

acid-base balance seems to be related to the occurrence of SDS and ascites because if

diet milliequivalent increaçes, the feed:gain ratio wiU also improve (Summers, 2994;

Surnrners, 1996). Olkowski and Classen (1998) reported that cardiac arrhythmias are

common among broiiers, and fast-growing broilers are more predisposed to them than

are other chickens. It seems that mhythmias play a significant role in the pathogenesis

of SDS. Grashom and El-Soud (1 994) suggested that Lipid peroxidation is linked to

the occurrence of SDS because peroxides could damage cefl membranes and hence

cause heart attack. Chung et al. (1993) pointed out that SDS is a cardiac dysfunction

coupled with change in the cardiac sarcoplasmic reticular membrane function, and that

dietary fat incIusion is involved in the incidence of SDS.

4.2.1 Effect of feed restriction on the incidence of sudden death syndrome

The application of feed restriction programs as a management technique for

reducing growth rate because of its association with the incidence of metaboiic

disorders such as SDS, ascites, and leg deformities has been investigated Powes et

al., 1988; Classen et al., 1991). Blair et al. (1993) studied the effect of continuous vs.

increasing photoperiod lighting in broiler chickens and reported that the

implementation of increasing lighting pattern significantly reduced overall mortality

as weI1 as rnortality from sudden death syndrome. A reduction in the incidence of SDS

in broiler chickens with the application of increasing lighting program was also

observed by OkSuk et al. (1998). Gonzales et al. (1998a) restrkted broiler chickens to

20% of ad libitum intake fiorn 8 to 21 days of age, and reported that feed restriction

reduced the mortality rate by 20%, and that Sudden Death Syndrome and ascites were

the main cause of mortality in birds fed ad libitum. However, other authors have not

obtained a reduction in the incidence of SDS mortality using sirnilar techniques

@obimon et al., 1992). This might be due to the shorter duration of feed restriction

applied. Gonzales et al. (1998b) suggested that SDS is related to high productivity,

and reported that there are ciifferences among strains of broilers for the occurrence of

SDS.

It is clear that the application of feed restriction regimens is an option for

decreasing the broiler's growth rate during certain periods of the growth period, and so

also reducing the incidence of mortaiïty fiom SDS and other metabolic disorders such

as ascites and leg deformities.

5. Summary

Research conducted in broiler chickens conceming cornpensatory growth has

intensified over the past 10 years. This is due to the potential advantage of improving

feed conversion while maintainhg normal market body weight for age, and somehow

reducing the incidence of ascites and SDS. The mechanisms conirolling compensatory

growth are related to reduced overall maintenance requirement, and an improved feed

efficiency for growth. The response of broiler chickens to growth compensation is due

to factors such as duration, timing, and duration of feed restriction, as well as sex and

genetics.

The effect of a mild feed restriction, either quantitative or qualitative,

thsoughout the productive life or at different periods needs to be evaluated in order to

determine if growth compensation occurs and if so, how it affects the productive

parameters of broiler chickens.

6. General objectives

The objectives of this thesis were:

1. To evaluate the effects of a mild feed restriction throughout the productive

life of broiler chickens.

2. To evaluate growth compensation in broiler chickens subjected to

qualitative feed restriction.

3. To evaluate the effect of mild feed restriction at different periods of the

productive life on potential for compensatory growth.

4. To determine the effect of qualitative and quantitative feed restriction on

carcass parameters in broiler chickens.

5. To determine the effect of mild feed restriction on ileal nitrogen digestibility

and AMEn.

CHAPTER III

EFFECT OF QUANTITATIVE AND QUALITATIVE FEED RESTRICTION

ON GRO'WTH AND PERFORMANCE ON BROILER CHICKENS

Two experïments were conducted to evaluate the effect of quantitative and

qualitative feed restriction on the pei-formance of broiler chickens. In the £kt

experiment, broilers fed identical pelleted diets were feed-restricted fiom 5 d to 42 d

by giving 95, 90, or 85% of the ad libitum feed consumed by control birds the

previous day. In a second experiment, broilers were fed either a pellet or masb com-

soybean based diet fiom 1 wk to 7 wk. Results fiom experiment 1 indicate that live

body weight at 42 days was significantly different between unrestricted and restricted

broilers (P c .01). Abdominal fat pad weight at 42 days was not significantly different.

among ad libitunz and restricted treatments- Feed efficiency at 42 days was not

affected by feed restriction, although a significant reduction in mortality was noted

when feed intake was reduced (P c .05). Feed-restrïcted broilers needed 2.4 (5% FR), . 4.4 (10% FR), and 5.3 (15% (FR) more days to reach the body weight attained by the

control group at 42 days. In the second experiment, broilers fed mash had lower live

body weight and breast meat yield at both 42 and 49 days (P < -05). Cumulative

mortality at both 42 and 49 days was reduced in broilers fed mash (P < .05). There

was no significant difference in feed conversion when comparing birds fed pellets or

mash. The significant decrease in mortality and the fact that feed efficiency was not

significantly affected provide interesting concepts for industry application.

(Key words: feed restriction, quantitative, pellets, mash, broiler performance)

INTRODUCTION

1t is generally assumed that the more feed that birds eat the greater the body

weight at market age. Barbato (1994) stated that the control mechanisms of feed intake

post-hatch are related to genetic selection for body weight. Improvement noted in

market body weight has been attained due to an increased feed consumption, which is

related to genetics (Havenstein et al., 1993) and supported by nutrition.

This improvement in body weight-for-age of modern broiler chickens, due to

an increased growth rate and higher nutrient metabolism, has led to a greater

occurrence of metabolic and skeletd disorders (Robinson et al., 1992), and increased

fat deposition vu and Robinson, 1992). Feed restriction programs have shown the

potential to reduce the incidence of ascites (Julian, 1997; Tottori et al., 1997), and

sudden death syndrome (SDS) (Blair et al., 1993; Gonzales et al., 1998a). These

conditions are more cornmonly observed in fast growing broilers that are full-fed. If

birds are allowed to consume feed ad libitum intake may surpasses their "nutrient

requirements". Broiler chickens fed ad libitum likely consume energy at a level two or

three times above their maintenance needs (Boekholt et al., 1994), and so fat

deposition is increased. This fact is of economical concem because fat represents an

undesirable and uneconornical product.

In order to produce a leaner bird and reduce the unfavourable effects of fat on

human health there is interest in the poultry industry in reducing fat deposition in

broiler carcasses. Results obtained from the use of feed restriction programs to reduce

the carcass fat content in broiler chickens have been inconsistent. Reduction in

abdominal fat pad content (AFP) has been noted by Plavnik and HuMritz (1991); Jones

and Farrell (1992b); Palo et al. (1995a); and Santoso et al. (1995). However, others

have failed to c o b this effect (Yu et ai., 1990; Fontana et al., 1993; Deaton, 1995;

Zubair and Leeson, 1996a). Such inconsistency may relate to different feeding

strategies applied, which rnay affect the birds response to feed restriction.

hprovement in feed efficiency noted with the use of feed restriction programs

is due to reduced overall maintenance requirements. This seems to be due to a

decrease in the basal metabolic rate in feed-restricted birds (Zubair and Leeson,

1994b) linked with a srnailer body weight during early growth, and this is due to birds

demands less energy for maintenance (Marks, 1 99 1). Consequently, there is current

interest in the use of feed restriction programs to modify the bird's pattern of growth,

so decreasing their maintenance requirements.

In an attempt to evaluate the bird's response to a mild feed restriction

throughout its Iife, and to alleviate some of the metabolic disorders affecting modem

broiler chickens, two experiments were conducted involving different feed textures

and levels of feed restriction,

MATERIALS AND METHODS

Experiment 1

Three hundred and sixty day-old male broiler chickens of a commercial strain

were randomly allocated to one of four treatrnents of 90 chicks each. Each treatment

consisted of three replicates of 30 birds each, located in 2.44 x 1.83 m floor pens. AU

birds were fed ad libitum to 5 d of age using a conventional starter diet (Table 3.1),

formulated to meet the nutrient requirements according to the NRC (1994). Lighting

was provided 23 Wday. Room temperature was maintained at 32.5 C from O to 5 d and

then gradually reduced according to standard brooding practices. At day 5, all birds

were wing-banded, and individually weighed. Control birds (fed ad Iibiturn) and feed-

restncted chicks received the starter, grower, and f i s h e r diets throughout the

different periods respectively. Starter diet was offered fiom 1 to 21 d, Bower diet

(Table 3.1) fiom 21 to 35 d, and fïnisher diet (Table 3.1) f?om 35 to 42 days of age.

AI1 diets were fonnulated to meet NRC (1994) nutrient requirement recornmendations.

Chicks in treatment 2, 3, and 4 were feed-restricted to 95%, 90%, and 85%

respectively of ad Zibittrm intake achieved by the control birds on the previous day

fiom 5 to 42 d of age*

Individual body weights were measured at 5, 7, 14, 21, 28, 35, and 42 days.

Pen feed intake and feed efficiency were also calculated. A11 dead birds were collected

daily and £kozen prior to post-mortem analyses. At 42 d of age a random sample of 8

birds per pen was taken and processed at the University of Guelph plant. Birds were

exsanguinated, immersed in 60 C water for 2 min, and plucked in a rotary dnim.

Viscera were manually removed and the abdominal fat pad weighed. Chilled carcasses

were weighed, the breast skin dissected, and the two main breast muscles of each side

of the carcasses were carefilly excised and weighed (Leeson et al., 1991). Regression

malysis of the complete growth data for each treahnent was used to create regression

equations which allowed extrapolation of growth fiom 42 to 50 days and expression of

the predicted body weight for each day duing that periods for each treatment.

Experiment 2

Three hundred and sixty day-old male broiler chickens of a commercial st ra in

were randomly allocated to one of three treatments of 120 chicks each. Roorn

temperature was maintained at 32.5 C fiom O to 5 d and then gradually reduced

according to standard brooding practices. Lighting was provided 23h/day, Each

treatment consisted of four replicates of 30 birds each, located in 2.44 x 1.83 m ffoor

pens. Al1 birds were fed ad libitum to 49 d of age using conventional starter, grower,

and finisher diets (Table 3.2) respectively. Each diet was fonnulated to meet the

nutrient requirements according to NRC (1994). Starter diet was offered fiorn I to 17

d, grower diet from 17 to 35 d, and finisher diet fiom 35 to 49 days of age. Control

birds in treatment 1 were fed these three sequential diets in a cnunbIe-pellet-pellet

fonn. Birds in treatrnent 2 were given feed as mash-pellet-mash, while those in

treatment 3 were given feed as mash-mash-pellet for the starter, grower, and riisher

diets respectively.

Individual body weights were measured at 17, 35, 42, and 49 days. Feed

consumption and feed efficiency data were recorded for the starter, grower, and

finisher intervals. Al1 mortalities were recorded daily and dead birds fiozen for

subsequent post-morten examination. At 42 and 49 d of age a random sample of 8

birds per pen was taken and processed as described for Experiment 1 at the University

of Guelph plant.

Statistical analysis

The experiments were antanged as a completely randomised design with pen as

the experirnental unit. All variables were subjected to a nested design procedure

anaIysis (SAS Institute, 1990). SDS and ascites data were subjected to analysis of

variance. Multiple cornparisons among means were made using Tukey's studentized

range test (Steel et al., 1997). Estimated body weigbt at which feed-restricted birds

reached ad Zibutim body weight at 42 d was subjected to linear regression mode1 (SAS

Institute, 1990).

RESULTS

Experiment 1

Broiler performance in relation to different levels of feed restriction is shown

in Table 3.3. Body weights among treatments were not significantly different at 5 days

of age. Body weight of birds at 28, 35, and 42 d were significantly different for most

treatments (P < .OS), and ad libitum fed birds had a significant Iarger body weight at

al1 ages. The reduction in body weight depended on the level of feed restriction

applied, with the smallest body weight noted in birds restricted by 15%. Overall

weight gain (Table 3.3) followed the same pattern as body weight. Feed intake

differed cornmensurate with the goals of the restriction program (Table 3.3). Feed

conversion ratio was not significantly different (P > -05) among control and feed-

restricted treatments, although the ad libitum fed birds had a numencally superior feed

conversion (Table 3.3). Mortality was only significantly different between ad libitum

and birds feed-restricted to 15% of previously ad libitum intake. It was observed

however, a trend to reduce mortality with the application of feed restriction, with the

highest mortaiity noted in ad Zibifum fed treatment. The incidence of sudden death

syndrome and ascites followed a reduction trend with the application of feed

restriction (Table 3.3). Carcass characteristics of broilers at 42 d are shown in Table

3.4. Breast meat yield and carcass weights were significantly different among

treatments. Ad libitum fed birds had supenor (P c .05) carcass weight and breast meat

yield, and a progressive reduction in both was noted with increasing feed restriction.

Abdominal fat pad weight was not significantly different among al1 treatments (Table

3.4) however, it was noted a decreasing trend with feed restriction. Breast meat as %

of carcass was reduced with the application of feed restriction (Table 3.4).

Broiler growth curves under different Ievels of feed restriction are shown in

Figure 3.1. It is noted that feed-restricted bùds showed a reduced growth rate, and this

is observable as early as 14 d (Figure 3.2). As birds get older, an increased difference

in the growth curve is observed among the control and feed-restricted treatments until

14 days of age. At t k s time the reduction in growth was 13, 17, and 19 % for the 5,

10, and 15 % feed-restncted birds respectively (Figure 3.2). After 14 d growth rates

are comparable for d l treatrnents. By 42 d restricted birds were smaller than control

birds (Figure 3.1), indicating that feed-restricted treatments were unabIe to

compensate body weight when comparing to ad libitum fed chicks.

The estimated body weight at which feed-restricted birds reached the weight

achieved by the ad libitum fed birds at 42 days of age is shown in Figure 3.3. Birds

feed-restricted to 95%, 90%, and 85% of ad libitum feed intake reached the 42 d

control body weight at 45,47, and 48 days respectively.

Table 3.5 shows the estimated income based on 200,000 broilers subjected to

the levels of feed restriction applied in this experhent. MortaIity and the esîimated

body weight obtained in each treatment were used as well as the estimated feed intake.

The pnce of feed and Iive weight was estimated as 18 cskg and 1.40 $/kg

respectively, As noted, a superior incomekrop is obtained with the use of feed

restriction, and this is due to a reduced mortality, which increases the Iive body weight

yielded per crop. This is of economic advantage in those countries where the numbers

of crop per year are reduced. However, yearly income is reduced because of the Iarger

grow-out time necessary with the restriction programs.

Experiment 2

Body weigfit and feed conversion of broilers given feeds of varying texture are

shown in Table 3.6. Initial body weights of broilers were not significantly different

among treatments. Body weight at 17,35,42 and 49 d of broiler chickens fed textured

diets throughout was significantly improved (P < -05) compared to those fed mash

diets at different periods. No significant difference (P c .05) was observed in weight of

birds fed mash diets during different periods at 17, 35, 42 or 49 d. Feed:gain ratio

during the starter period was improved in broilers fed textured compared to those fed

mash diets, however during the grower and finisher period feed conversion was

irnproved (P < -05) in broilers fed mash diets. Cumulative feed conversion to either 42

or 49 d was not different among treatments (P > .05), but a numericdly superior feed

conversion was noted in mash fed birds. Feed intake and mortality of broilers fed

altering texture diets are shown in Table 3.7. Feed intake at either 42 or 49 d of broiler

chickens fed textured diets throughout was simiificantly increased (P c -05) compared

to those fed mash diets at different periods. Mortality during the starter and grower

periods was not significantly different (P > .OS) across treatments, however a

significant reduction (P c -05) in mortality was observed during the finisher penod (35

to 42 d) between broilers fed textured and untextured diets. A significant reduction in

cumulative mortality at either 42 or 49 d (P < .01) was observed when broilers were

fed mash diets during the starter and fïnisher periods (Table 3 3 , and a numerical

reduction in mortality was noted in broilers fed mash diets during the starter and

grower penods compared to c-p-p fed broilers. Mortality from sudden death syndrome

and ascites was not different across treatments (P > .OS), but there was a trend towards

decreases in these disorders in rnash-fed birds. Carcass characteristics of broilers at 42

and 49 d under qualitative feed restriction are shown in Table 3.8. Breast meat yield at

either 42 or 49 d was significantly greater in chicks fed only textured diets, and no

differences were obtained between treatments using mash diets at different periods

(Table 3.8). There was Iess abdominal fat in mash-fed birds, with birds fiom treatment

2 hawig the smallest (F' < .05) abdominal fat pad weight at 42 d. There was no

difference in abdominal fat pad weight at 49 d of age (P > .05).

DISCUSSION

Feed restriction clearly affected body weight, weight gain, mortality, breast

meat yield, carcass weight, and breast meat as a % of carcass (Table 3.3, and 3.4). The

degree of change in these parameters depended on the level of feed restriction used.

There was a reduction in body weight at 42 d of about 8, 14, and 17% for chicks

restricted to 95, 90, and 85% respectively of ad libitum feed întake relative to the

previous days' intake of the control birds. Such a reduction in body weight is in accord

with results fkom Khantaprab et al. (1997), Roth et al. (1993), and Santoso et al.

(1993a). The level of reduction in breast meat yield was more severe than that for

body weight, being 13, 20, and 26.6% respectively, which suggests that feed

restriction specificdly reduced breast muscle growth (Khantaprab et al,, 1997; GiUe et

al., 1992), and that this effect again depends on the level of feed restriction. An

allometric relationship, where breast meat yield Vary sfightly as feather-fiee weight,

exists between development of breast meat and body weight (Gous et al., 1999), and

this relationship seems to change as severity of feed restriction increases. It is also

possible that reduction in breast meat yield in feed-restricted birds might be due to

lowering amino acid intake linked with decreasing enerav levels. Results suggest that

the growth rate of broiler chickens is related to feed intake, which supports the

statement that improvement in body weight of birds is highly correlated to feed

consumption (O 'Sullivan et al ., 1992). Abdominal fat deposition was not significantly

affected by the implementation of feed restriction, confirming the results of Santoso et

al. (1993b), Fontana et al. (1993), Deaton (1995), and Zubair and Leeson (1996a),

although feed-restricted birds showed a numerically idenor abdominal fat pad weight.

The fact that there was no significant reduction in abdominal fat deposition in this

experiment suggest that even 'feed-restricted' broiler chickens are still "overeating",

and that the level of feed intake may control de novo lipogenesis (Rosebrough and

McMurty, 1993). Moreover, Boekholt et al. (1994) stated that ad libitum fed broilers

are consuming energy at a rate nearly 2 to 3 times their maintenance requirements.

Although feed conversion was not significantly different among treatments, ad libitum

fed birds had a numerically superior feed conversion.

Broiler growth patterns folIow a sigrnoid shape independent of the feed

restriction program used (Figure 3.1), and restricted birds had a similar growth pattern

to the control birds fiom 21 to 49 d. The most noticeable difference in growth is that

up to 24 d of age, restricted birds had reduced growth of about 13, 17 and 19%

respectively for treatments 2-4 (Figure 3.2). This may occur because at this time

proportionally more nutrients go towards growth rather than for maintenance needs

(Leeson and Summers, 1997). M e r this period differences between the growth curves

decrease progressively over tirne.

As shown in Table 3.5 the application of feed restriction increased the income

for any one crop, and this is due to a reduced mortality obtained in feed-restricted

broilers, which increase the total birds rnarketed. However, less incorne/year is

obtained with restncted treatments because the total crops/year are reduced. This is

due to the fact that feed-restricted birds need to be grown for 2.2,4.4, or 5.3 more days

respectively to reach market body weight, increasing the total food consurnption per

bird while decreasing the nurnber of crops possible each year.

The two main metabolic disorders affecting todays broiler chickens are ascites

and sudden death syndrome (SDS), and these pathologie conditions are closely related

to rapid growth rate and increased feed intake. In the first experiment the

implementation of feed restriction did not significantly reduce the prevalence of these

disorders, and this is in agreement with observations of McGovern et al. (1997), and

Robinson et al- (1992), but contrary to Julian (1997), Tottori et al. (1997), and

Gonzales et al. (1998a). However, it was noted a decreasing trend in these disorders

when feed restriction was applied. Such variance in the occurrence of these disorders

arnong researchers rnay to be related to the severity of feed restriction used and to

other uncontrollable factors such as bird strain. It is likely that in order to signihcantly

decrease the incidence of SDS, more severe under-nutrition is required.

Changing feed texture significantly uifluenced body weight, feed intake,

mortality, breast meat yield, abdominal fat pad size, and carcass weigbt (Table 3.6, 3.7

and 3.8). The birds fed crumble-pellets had a superior performance compared to birds

fed mash at any time. Body weight of birds fed mash was reduced by about 9% and

8% compared to pelleted fed birds at 42 and 49 d respectively. No differences in body

weight, feed intake, mortaliiy, breast meat yield, and carcass weight were observed

between mash-pellet-mash and mash-mash-pellet fed birds. Improvement in body

weight in pellet-fed birds is in agreement with those observations of Plavnik et al.

(1997), and Hamilton and Proudfoot (1995), Feed intake was increased in birds fed

pellets. The greater response in body weight of birds fed pelleted diets rnay be linked

to some extent to increased feed consumption. Nir et al. (1994) stated that increased

feed consumption is positively reIated to the quality of pelleting when comparing to

mash. This improvement in broiler performance with pelleted diets may be attributable

to greater digestibility of carbohydrates and an associated increase in daily nutrient

intake (Hamilton and Proudfoot, 1995; Nir et al., 1995), and/or less feed wastage

(Savory, 1974). Mortality was greater in birds fed pelleted diets than those fed mash

and this is in accord with Nir et al. (1995). The increased mortality observed in birds

fed pelleted diets might be linked to reduced bird activity (Nir et al., 1995) because

these birds spend less time and energy feeciïng. However, Jones at el. (1995) who fed

mash or pellet diets to 42 days of age, reported no significant differences in mortdity

between mash and pellet fed birds. Mortality fiom SDS and ascites were not

significantly reduced in treatment 2 and 3, although a trend to reduce these disorders

was noted. Nir et al. (1995) did show feed restriction to reduce the incidence of

ascites. Abdominal fat pad size was significantly decreased in birds fed mash-pellet-

mash diets at 42 days of age, suggesting that the qualitative restriction applied was

enough to lower the rate of lipogenesis (Rosebrough and McMurtry, 1993) in mash

fed birds. Breast meat yield at 42 and 49 d was reduced by 13 and Il%, and 13 and

10% in mash fed birds (treatment 2 and 3 respectively). These results are contrary to

observations of Jones et al. (1995) who showed no deletenous effect of mash feeds on

breast yield.

CONCLUSIONS

Continuous feed restriction slows the growth of broilers and reduces rnortality.

Extended grow-out tirne for feed-restricteà birds decreased estirnated total yearly

incorne. Using mash diets in any growing period reduced growth rate, but resulted in a

reduced rnortality. It can be concluded that the application of continuous feed

restriction will be based on production goals, and can be used when the number of

crops per year is not affected.

Table 3.1. Diet composition, Experiment 1.

Starter Grower Finisher Ingredients (%)

Diet I Diet 2 Diet 3

Soybean meal (48%) Yellow corn Wheat Animal-Vegetable fat Lirnestone Dicalcium phosphate Salt Vitamin-mineral premix * D,L-Methionine

Calculated analysis

ME @ c m @ 3096 3 141 3181 Cnide protein (%) 23 .O3 20.21 18.18 Lysine (%) 1.33 1.1 1 0.96 Methionine+cystine (%) 0.90 0.73 0.64 Calcium (%) 1-00 0.94 0.86 Available phosphoms (%) 0.45 0.40 0.37

* Supplieci per kilogram of diet: vitamin A, 8,000 KJ (retinyl palmitate); cholecalciferoI,40 ug; vitamin E, 11.0 IU (dl-a-tocopheryl acetate); riboflavin, 9.0 mg; biotin, 0.25 mg; pantothenic acid, 11.0 mg; vitamin BIL , 13ug; niacin, 26 mg; choline, 900 mg; vitamin K, 1.5 mg; folk acid, 1.5 mg; ethoxyquin, 125 mg; manganese, 55 mg; zinc, 50 mg; copper, 5 mg; iron, 30 mg; and selenium, 0.1 mg.

Table 3.2. Diet composition, Experiment 2.

Ingredients (%) Starter Grower Finisher

Soybean meal (48%) Yellow corn Animal-Vegetable fat Limestone Dicalcium phosphate Salt Vitamin-minerd premix * D,L-Methionine Coban S tafac

Caiculated analysis

ME @camg) 3050 3150 3200 Cnide protein (%) 22.3 1 20.00 18.00 Lysine (%) 1.27 1-10 0.95 Methionine+cystine (%) 0.82 0.74 0.64 Calcium (%) 1 .O0 0.92 0.90 Available phosphoms (%) 0.42 0.40 0.38

* Suppiied per kilogram of diet: vitamin A, 8,800 IU (retinyl palmitate); cholecalciferol, 3,300IU; vitamin E, 40 IU (di-or-tocopheryl acetate); nioflavin, 8.0 mg; biotin, 0.22 mg; thiamïn, 4 mg; pantothenic acid, 15.0 mg; vitamin B 12 ug; niacin, 50 mg; choline, 600 mg; vitamin K, 3.3 mg; folk acid, 1.0 mg; ethoxyquin, 120 mg; manganese, 70 mg; zinc, 70 mg; copper, IO mg; iron, 60 mg; and selenium, 0.3 mg.

Table 3.3, Broiler performance in relation to feed restriction. Ex~erirnent 1,

Body Weight Weight gain Feed Intake Feed : gain Mortality SDS Ascites Feed restriction1 (s) (9) (g) Ratio (%) (%)

ad libittint 1354" 1838' 2401a 2359* 4155.7a 1.68 5.6" 3.3 2.0 5 1 2 1 3 ~ 1 6 ~ 2 ~ 2201b 215gb 39 15 .(iUb 1.76 4Sab 1.1 0.0 10 1164' 1 Wb' 2063~' 2057~' 371 1 .2b' 1.75 3.2ab 2.2 0,O 15 1118' 1509' 1997' 1956' 35 13.4' 1.78 1.lb 1.1 0.0 SEM 20 23 38 49 75 0.03 0.7 0,s 0.4

Means within a colurnn wiih no common superscripts differ significantly (P < .OS) 'Slarting at 5 d of age

Table 3.4. Carcass characteristics of broilers at 42 days of age subjected to different levels of feed restriction, Experiment 1.

Feed restriction Carcass Breast Meat Abdominal Fat Pad Breast Meat a s % C W 1

Ad libitum 1 849.2' 397.7a 49.1 21.5' 5 1716.1b 346.1 46.1 20.1 ab

10 1625. gbe 3 1 Ob' 46.5 1 9.4b 15 15 18.5' 292.2' 44.4 1 9.Zb

SEM 20.4 6.1 1.2 0.2

'' Menns within a colurnn with no cornnion superscripis dirt'cr significantly (P C ,05) ' CW: cnrcoss wçighl,

Table 3.5. Income estimation projected to 100,000 broilers subjected to feed restriction, Experiment 1.

Feed Projected Total Days Feed Intake restriction Body Mortality Birds Need (kg) Body Weight Incoine Crops Incomelyear

(%) Weight (g) % marketed Per crop per bird (tonnes) per crop ($) per year ($ million)

Fecd os ot 1 8cf/kg Livc wt ns nt 1.40 $/kg

Table 3.6. Effect of feed texture on body weieht of broilers, Experiment 2.

Treatment Body Weight (g) Feed Intake: Weight gain

17 d 35 d 42 d 49 d O-17d 17 -35d 35 -42d 42-49d 0 - 4 2 d 0-49d

C-p-p1 576 " 2087 " 2658 " 3249 1.34 1.81 2.42 a 2.46 1.82 1.90

m-p-m2 479 1956b 2414b 2973 1 .52 1.66 2.32" 2.65 1.76 1.88

SEM 5 13 16 23 0.03 0.03 0.07 0.1 1 0.02 0.02

i-b , Means within a column with no comnwn superscripts diffcr signilicantly (P < .OS) I crumble-pellet-pellet diet

mash-pellet-mash diet ' maoli-mash-pellet diet

Table 3.7. Effect of feed textures on feed intake and mortality in broilers, Experiment 2.

Treatment Feed lntake (g) Mortality (%) SDS Ascites (%)

C-p-p1 4452.7 a 5872.2 a 4.9 3.4 5.5 1.9 13.9 a 15.7 a 7.5 2.5 Vi w m-p-m2 4122.5 5546.9 4.2 0.9 0.9 0.9 5.9 6.8 1.6 0.8

m-m-p3 4151.8b 5524Sb 2.5 4.3 0.9 0.9 7.6 ab 8.5 ab 2.4 0.0 SEM 56.6 66.6 0.8 0.8 0.8 0.5 1.4 1 .6 1.2 . 0.5

- -

Mcans within n column with no cornmon supcrscripts diffcr significantly (P < ,05) ' cmrnble-pellet-pellet diet mash-pellet-mash diet mash-mash-pellet diet

Table 3.8. Carcass characteristics in broilers fed different feed textures. Experiment 2.

Treatment Carcass Weight (g) Abdominal Fat Pad (g) Breast Meat (g)

c- p- p' 2048 a 2494 a 50a 69 452 a m - p - m 2

551 a

1792 2278 44 61 390 481 m - m - p 3 1881'" 2338 ab 45ab 72 402 495 SEM 21 27 1.3 2.2 5.8 8.5

'', Means within a column wiih no comnnin superscripis diffcr significonily (P < .05) ' crumble-pellet-pellet diet 2 mash-pellet-mash diet

' mash-mash-pellet diet

W W W

CHAPTER IV

EFFECT OF EARLY AND LATE QUANTITATIVE FEED RESTRICTION ON

G R O W H AND PERFORMANCE IN BROILER CHICKENS

ABSTRACT

Two experiments were carried out to evaluate the effect of mild feed

restriction, at different periods, on broiler performance up to 42 and 49 days of age, In

experiment 1 broilers were feed-restricted to 90 % of the ad libitum intake of a control

group fkom 5 to 9, 5 to 14, 5 to 19,s to 24, or 5 to 29 days respectively. In experiment

2 broilers followed the same feed restriction but fkom 14 to 17, 14 to 20, 14 to 23, 14

to 26, or 14 to 29 days, Results fiom Experïment 1 indicate that both body weight and

mortality were not significantly different (P > -05) at 42 days across treatments,

although at 49 d there was a significant reduction (P c -05) in mortality across

treatments. There was a significant (P < -01) linear improvement on feed conversion

arnong ad libitum and feed-restricted treatments at 42 d. At both 42 or 49 d during the

second experirnent there was no significant difference (P > -05) in body weight or

mortality across treatments. There was a significant (P < -05) linear decline in breast

meat yield due to feed restriction at 42 d, but no clifferences (P > -05) were observed at

49 d (Experiment 1 and 2). Other carcass characteristics were not significantly

different at both 42 and 49 d (P > .05) (Experiment 2). Mild feed restriction allowed

birds to exhibit full compensatory growth. Restricting feed intake at an earlier stage (5

d) resulted in more beneficial productive parameters.

(Key words: feed restriction, compensatory growth, broilers, productive parameters)

INTRODUCTION

It is assumed that the maximum growth rate of an animal is genetically

predetermined, and that each animal follows a conventional growth curve when

conditions are favorable. If birds attain market body weight in a shorter time period,

feed efficiency will be improved due to a decrease in their overall maintenance

nutrient requirements (Leeson and Summers, 1997). For this reason there is curent

interest in the use of feed restriction programs to modi@ the birds pattern of growth,

thereby decreasing their maintenance requirements. The use of mild feed restriction

can be an alternative to modim the broiler growth curve while attaining market body

weight for age. Usually the growth curve of broiler chickens fed ad libitum has a

sigmoid form (Walker et aI., 1995), although because birds do not grow at an even

rate, the growth pattern may Vary fiom bird to bird. Birds subjected to feed restriction

have a slower growth rate at the beginning of the growth period compared to ad

libitum fed chicks. This reduced growth decreases the bird's overall maintenance

requirements, thereby improving feed efficiency if market body weight is attained.

Feed restriction regkens have been normally implemented at an early age, but no

studies have compared mild feed restriction at early and Iate stages. Cornplete

compensatory growth and improved feed efficiency in broiler chickens under early

feed restriction progams have been recorded by Plavnik and Hurwitz (1990), Santoso

et al. (1993b), Zubair and Leeson (1994a), and Deaton (1995). Other workers

however, have failed to show complete compensatory growth in broiler chickens

under similar nutritional conditions (Fontana et al., 1992; Ramlah et al., 1996;

Cristofori et al., 1997). Birds exhibiting such reduced growth during a restriction

period have reduced plasma concentrations of insulin-like growth factors (IGF-1 and

II) and this reduction is related to the degree of feed restriction (Leili et al., 1997),

which helps explain reduced growth. When normal feed strategies are restored, chicks

grow at a higher rate than normal ui order to attain normal weight for age. This

accelerated grocvth observed when the feed restriction is ended may be due to higher

levels of g r o d hormone (GH) observed in birds previously feed-restricted (Buyse et

al., 1997). Compensatory growth can be accomplished when birds divert more energy

for growth or if the existing energy is utihed in a different manner (Ryan, 1990). The

mechanisms involved in this process seem to be related to reduced maintenance

requirernents, an increased food intake relative to body size, alteration in the

proportion of fat and protein deposited in the tissues, or improved feed efficiency for

growth (Ryan, 1990; Rowan et al., 1996). Tbe energy that sustains the accelerated

growth may come fiom a reduction in the overall maintenance energy needs (Yu and

Robinson, 1992), andor to a decrease in the basal metabolic rate noted in feed-

restricted birds (Zubair and Leeson, 1994b)- Another potential advantage in reducing

early growth rate in broiler chickens is reduced mortality caused by metabolic

disorders, which are related to fast growth in birds that are full fed.

The application of feed restriction, which then allows a complete

recovery of body weight as well as a leaner body, is of economic importance. Zn an

attempt to modifjl the broiler growth curve, by exerting minimum stress on the broiler

while attaining normal market weight for age, two experiments involving feed

restriction were carried out using miId feed restriction at different intervals.

MATEXMLS AND METHODS

General procedures

In each of the 2 experirnents conducted, 360 day-old male broiler chickens of a

commercial strain were randornly allocated to one of six treatments of 60 chicks each.

Each treatment consisted of two replicates of 30 birds each, located in 2.44 x 1.83 rn

floor pens. Lighting was provided 23Wday. Room temperature was maintained at 32.5

C f7om O to 5 d and then gradually reduced according to standard brooding practices.

Control birds (ad libitum) and feed-reseicted birds received the starter, grower, and

nnisher diets throughout the different periods respectively (Table 4.1). Starter diet was

offered fiom 1 to 21 d, grower diet fiom 21 to 35 d, and nnisher diet fiom 35 to 42

days of age.

Individual body weights were measured at 7, 14, 2 1, 28, 35, 42, and 49 days.

Pen feed intake and feed efficiency were also calculated. Al1 dead birds were collected

daily, and fiozen pnor to post-mortem analyses to determine cause of death. At 42 and

49 d of age, random sarnples of 10 birds per pen were processed at the University of

Guelph plant. Birds were exsanguinated, irnmersed in 60 C water for 2 min, and

plucked in a rotaxy drum. Viscera was manually removed and the abdominal fat pad

weighed. Chilled carcasses were weighed, the breast skin dissected, and the two main

breast muscles of each side of the carcasses were carefully excised and weighed

(Leeson et al., 1991).

Experiment 1

Al1 birds were fed ad libitum to 4 d of age using a conventional starter diet

(Table 4.1), formulated to meet nutrient requirements according to NRC (1994). At

day 7, al1 birds were wing-banded, and individually weighed. Chicks were fed ad

libitum (control) or feed-restricted to 90% of the ad libitum intake (recorded the

previous day for the control birds) fiom 5 to 9 (treatment 2), 5 to 14 (treatment 3), 5 to

19 (treatment 4), 5 to 24 (treatment 5), or 5 to 29 (treatment 6) days respectively.

Experiment 2

A11 birds were fed ad libitum to 13 d of age using a conventional starter diet

(Table 4. l), formdated to meet the nutrient requirements according to NRC (1994).

At day 14, al1 birds were wing-banded, and individually weighed. Chicks were fed ad

libitum (control) or feed-restricted to 90% of ad libitum intake fiom 14 to 17

(treatment 2), 14 to 20 (treatment 3), 14 to 23 (beatment 4), 14 to 26 (treatrnent S), or

14 to 29 (treatment 6) days respectively.

Statistical analysis

The experiments were manged as a completely randomized design with pen as

the experimental unit. Al1 variables were subjected to orthogonal contrasts analysis

(Steel et al., 1997). SDS and ascites were subjected to ANOVA procedure (Steel et al.,

1997). Feed conversion and mortality in experiment 1 were analyzed by linear

regression.

Experiment 1

Broiler performance in relation to different periods of restricted feeding to

90% of ad libittirn feed intake is shown in Table 4.2. Body weight of chicks at 35, 42,

and 49 days of age were not significantly different for most treatments (P > -05);

however, ad libitum fed birds were always numerically heaviest. Feed conversion (F:

G) showed a significant linear effect Q? < -01) among ad libitum and feed-restricted

treatments at 42 d (Figure 4.1). Akhough at 49 d there was no significant linear effect

(P > .05) among feed-restricted and ad libitum birds, the feed-restricted treatments had

a trend towards improved feed conversion (Table 4.2). No significant effect (P > -05)

was observed in mortality across most of treatments at 42 d, although feed-restricted

birds tended to have reduced mortality compared to ad libitum fed birds. At 49 d there

was a significant linear effect (P < -05) in rnortality across treatments (Table 4.2).

Mortality from ascites was not different (P < .05) across treatments. Restricting feed

fiom 5 to 30 d resulted in a lower mortality fiom SDS compared to ad libitum fed

birds (P c .OS). No significant differences were observed in SDS among feed-

restricted treatments. Carcass characteristics of broilers at 42 and 49 d are shown in

Table 4.3. At 42 d, ad libitum fed birds had superior (P c -05) breast meat yield, and a

progressive reduction was noted when an extended period of feed restriction was used

(Table 4.3). At 49 d there was no significant difference in breast meat yield (P > .05)

across treatments. Breast meat as a percentage of carcass weight decreased

significantly as a iinear effect (P < 01) cornparing ad libitum and feed-restricted

treatments at 42 d (Table 4.3). No significant differences were obsemed in breast meat

as a percentage of carcass weight across treatments at 49 days of age. Thigh portion

was not significantly aec ted by feed restriction at either 42 or 49 d among alI

treatments. Carcass weights followed the same trend as did thigh yield (Table 4.3).

Abdominal fat pad was not significantiy different (P > -05) among feed-restricted and

ad libitum fed birds (Table 4.3).

Broiler growth curves reIated to different times of feed restriction are shown in

Figure 4.3. Feed-restricted birds grew more slowly, and this situation depended on the

duration of feed restriction (Figure 4.3). Reduction in growth rate was noticed as early

as 14 d (Figure 4.3). At this time, reduction in the growth was 3.7, 15.6, 27, 17.3, and

16.6% for the 5 to 10, 5 to 15, 5 to 20, 5 to 25, and 5 to 30 d feed restriction periods

respectively (Figure 4.3). By 35 d, restricted birds were 2.8, 0.5, 1, 1.7, and 5%

smaller than ad libitum chicks (Table 4.2), suggesting compensatory growth according

to the larger differences observed at an earlier stage. At 49 d these differences are

further decreased (1, 1,0.2,0.6, or 3% respectively), indicating that the longer time for

market age, the more opportunity to achieve normal body weight.

Experiment 2

Broiler pedormance of birds feed-restricted for different periods of 90% of ad

libitum previous intake starting at 14 days of age is shown in Table 4.4. There was a

significant linear decline in 35 d weights related to days on restricted feeding (P < -05,

Table 4.4), although body weight at both 42 and 49 d was not significantly (P > .05)

different across treatments. No significant effect of restriction period (P > -05) was

noted in feed conversion at either 42 or 49 d, but feed-restricted birds tended to

improve feed conversion compared to ad Zibihrm fed chicks (Table 4.4). No significant

differences (P > -05) were observed in mortality across treatments at either 42 or 49

days of age (Table 4.4). Treatment had no effect on mortality fkom sudden death

syndrome (SDS) and ascites (P > -05, Table 4.4). Carcass characteristics at 42 and 49

days of age are shown in Table 4.5. There was a significant (P c -05) hear deche in

breast meat yield due to feed restriction at 42 d (Table 4.9, although no significant

differences (P > .05) were seen at 49 d. Thigh, abdominal fat pad, carcass weight, and

breast meat as a percentage of carcass weight were not significantly aec ted by feed

restriction (P > .05) at either 42 or 49 days of age (Table 4.5). Although no

significance differences were observed in thigh, carcass weight, and breast meat as a

percentage of carcass weight, ad libitum fed birds tended to have higher yields.

Growth curves of broilers subjected to different periods of feed restriction are

show in Figure 4.4. As previously noted, feed-reshicted birds had reduced growth,

and this was observable at 21 d (Figure 4.4). At this time, reduction in growth was

12.3, 9.4, 12.5, 13.0, and 12.7% for birds feed-restricted Eom 14 to 17, 14 to 20, 14 to

23, 14 to 26, and 14 to 29 respectively (Figure 4.4). By 35 days of age, the growth of

feed-restricted chicks were 2.2, 5.1, 3.8, 3.5, and 6.8% lower than ad libitum fed

chicks (TabIe 4.4), while by 49 days of age values of 0.8, 1.9, 0.2, 0.7, or 3.9 %

respectively are seen (Table 4.4), again indicating some growth compensation. These

differences were smaller, which indicates that allowing a longer penod to attain

market age will increase the opportunity for feed-restricted birds to attain control body

weight.

DISCUSSION

Feed-restricted birds were able to attain normal market body weight at both 42

and 49 days of age, which suggests growth compensation occurred. The response of

broiler chickens to growth compensation after a period of feed restriction may Vary

due to factors such as duration, timing, and severity of restriction and sex or strain of

birds. The duration and severity of the feed restriction used in both experiments

allowed birds to attain market body weight for age. Compensatory growth has been

achieved by broilers following short periods of undernutrition (Ballay et al., 1992;

Santoso et al., 1993b; Deaton, 2995). Other workers, however, have failed to attain

growth compensation in feed-restricted broilers fiom 4 to 7 or 7 to 14 days (Fontana et

al., 1992; Pa10 et al., 1995;sb). The energy to support accelerated growth may corne

from a reduction in the overall maintenance energy needs (Yu and Robinson, 1992),

and/or fi-om a decrease in the basal nietabolic rate as observed in feed-restricted birds

(Zubair and Leeson, 1994b). Cristofori et al. (1997) restricted the feed of broilers

£kom 7 to 21, 7 to 28 or 21 to 35 and showed that restricted birds did not cornpensate

in final body weight. This is in contrast to the results obtained in current experiments

where complete compensatory growth was attauied by feed-restricted birds. These

differences rnay have occurred due to the more severe degree of feed restriction

applied by Cristofori et al. (1997) due to they allowed 1.5 Mcal MEB W." /d. This

indicates that the severity of feed restriction is as important as the duration of

'

restriction for growth compensation in broilers.

During the £ht experiment, where feed restriction was applied at an earlier

age, feed conversion at 42 d was significantly improved with longer periods of feed

restriction. Similar results have been reported by Deaton (1995), and Cristofori et al.

(1997). No improvement in feed conversion was seen at 49 d in Experiment 1 or when

restriction was initiated Iater (experiment 2) in agreement with the results of Roth et

al. (1993). However, there were numerical improvements seen in experiment 2, and

feed conversion is numerically related to duration of restriction. The improvement in

feed conversion noted with the use of early feed restriction was likely due to reduced

maintenance requirernents, This perhaps relates to a decrease in basal rnetabolic rate

(Zubair and Leeson, 1994b) associated with a smaller body weight during early

growth. Feed-restricting birds at an earlier age significantly reduced mortdity at 49 d

in Experiment 1. This effect was not, however, observed in birds feed-restricted

starting at 14 d (experiment 2). It appears that the application of a feed restriction

program at an early penod (5 d) is more effective for reducing the growth rate of birds,

and also for decreasing the incidence of mortality caused by metabolic disorders. The

implementation of an early 5 d feed restriction program significantly reduced the

prevalence of sudden death syndrome (SDS), and this is in accord with observations of

Gonzales et al. (1998a), and OkSuk et al. (1998), who began the restriction penod at 5

or 8 d respectively, but contrary to the findings of Robinson et al. (1992) who

restricted at 7 d of age. Reduction in the prevalence of SDS seems to be reIated to a

decrease in growth rate, and to a diminution in activity (Gonzales et al., 1998) which

suggests some reduction in maintenance requirements. This discrepancy may be

related to the duration and seventy of the feed restriction applied. Mortality fkom SDS

and ascites was not affected when feed restriction was started at 14 d. These results are

In agreement with the observations of Robinson et al. (1992), and McGovern et al.

(1997)- It seems that feed restriction must be started early in order to be beneficial in

terms of improved liveability.

Breast meat yield was significantly reduced for feed-restricted birds oniy at 42

days of age, but not at 49 d. Reduction in breast meat at 42 d during the first

experiment was about 5% for chicks feed-restricted ftom 5 to IO, 5 to 15, 5 to 20, and

5 to 25, and 11% fiom 5 to30, suggesting that the longer the penod of restriction the

greater the reduction in breast meat yield. During the second experiment, breast meat

reduction was 4, 6.9,6.4,4, and 8% respectively for birds feed-restricted fiom 5 to 10,

5 to 15, 5 to 20,5 to 25, and 5 to 30. These results suggest that feed restriction reduced

breast muscle growth (Khantaprab et al., 1997), and that this effect is related to the

duration of feed restriction applied. No differences were observed in thigh portion

yield in either experiment at 42 or 49 d, indicating that the feed restriction applied did

not affect this parameter. Similarly, no significant differences were observed in

abdominal fat pad size in both experiments at 42 or 49 d. It was observed, however,

that fat pad size was greater in feed-resûicted birds at either 42 or 49 d in both

experirnents, suggesting that the level of intake allowed the synthesis of abdominal fat.

This may occur due to rnild feed restriction was not severe enough to reduce

sufficiently the energy intake and hence abdominal fat deposition, maybe because ad

libitum fed birds are over-consuming 2 to 3 times their energy maintenance

requirements (Boekholt et al., 1994). This is in accord with observations of Santoso et

al. (1993ab), Fontana et al. (1993), Susbila et al. (1994), Deaton (1995), and Zubair

and Leeson (1996a). This response might be related to the program of feed restriction

used. It seems to be that a more severe and longer tirne of feed restriction is necessary

to significantly reduce abdominal fat content, Breast meat as a percentage of carcass

weight was only signincantly affected in feed-restricted birds at 42 d during the Grst

experiment. This follows the sarne trend as for breast meat yield.

CONCLUSIONS

Feed restriction for various times early in gruwth at 90% of ad libitum feed

intake allowed birds to achieve complete growth compensation. The irnplementation

of feed restriction at an earlier stage (5 d) resulted in more beneficiai productive

parameters than did feed restriction starting at a later stage (14 d).

It can be concluded that the application of mild early rather than mild late feed

restriction in broiler chickens is suggested due to the irnproved response observed in

birds in relation to feed conversion and mortality.

Table 4.1. Diet composition.

Ingredients (%)

- -- - - - -

Starter Grower Finisher

Soybean meal (48%) Yellow corn Animal-Vegetab le fat Limes tone Dicalcium phosphate Salt

Calculated analysis

ME (kcawz) Cnide protein (%) Lysine (%) Methioninetcystine (%) Calcium (%) Available phosphorus (%)

* Supplied per kilogram of diet: vitamin A, 8,800 IU (retinyl palmitate); choIecalciferol, 3,300IU; vitamin E, 40 IU (dl-a-tocopheryl acetate); nioflavin, 8.0 mg; biotin, 0.22 mg; thiarnin, 4 mg; pantothenic acid, 15.0 mg; vitamin BIz, 12 ug; niacin, 50 mg; choline, 600 mg; vitamin K, 3.3 mg; folk acid, 1.0 mg; ethoxyquin, 120 mg; manganese, 70 mg; zinc, 70 mg; copper, 10 mg; iron, 60 mg; and selenium, 0.3mg.

Table 4.2. Performance of broilers subjected to feed restriction for varying time periods starting at day 5, Experiment 1.

orfaljfv (Oh)

Body Weight (g) Feed Intake: Total Mortality SDS Asci tes Feed Restriction Weight gain

ad libitum r 5 to 10

5 t o 15 5 to 20 5 to 25 5 to 30 SEM Linear Quadratic

i -b Mcans in a column wi\h no comrnon superscripts diflcr signilicanity (P c ,05) * (P < .OS) +* (P < .01) SEM: standard crror of mcan ns: non significanl

Table 4.3. Carcass characteristics of broilers subjected to feed restriction for varying time periods starting at day 5, Experiment 1.

Days I 42d 49d 42d 49d 42d 49d 42d 49d 42d 49d

Feed Restriction

ad lilritunr 5 to 10 5 to 15 5 to 20 5 to 25 5 to 30 SEM Linear Quadratic

Breast Meat Thigh Abdominal Fat Carcass Weight Breast Meat as (g) (g) Pad (g) (g) % CW'

-- --

'CW: carçass weighi SEM: standard m o t of mcnn * (P < .OS) ** (P < .01) lis: non significant

Table 4.4. Performance of broilers subjected to feed restriction for varying time periods starting at day 14, Experiment 2.

Feed Intake: Mortality (%) Peed Restriction Body Weight (g) Weight gain Total Mortality SDS Ascites

Days 35d 42 d 49d 42d 49d O-42d O 4 9 d O - 49d O - 49d

ad libiirrm 14 to 17

4 w 14 to 20 14 to 23 14 to 26 14 to 29 SEM Linear Quadratic

- - . - - - - -- - - --

SEM: Standard emr of mcan ' (P c .OS) ** (P c ,01) ns: non significant

Table 4.5. Carcass characteristics of broilers subjected to feed restriction for varying time periods starting at day 14, Experiment 2.

ad libitum 14 to 17 14 to 20 14 to 23 14 to 26 14 to 29 SEM Linear Quadratic

Peed Restriction

- -- - -p

(P < .OS) ns: nan significanl ns: non significant

Breast Meat Thigh Abdominal Fat Carcass Weight Breast Meat as (9) (g) Pad (g) (s) % cw

Figure 4.l.Feed Conversionat 42 d Related To Days Of Feed Restriction Starting At Day 5 (Exp 1)

10 15 20

Days Of Restriction

Figure 4.4. Broiler growth curve from 7 to 28 days (Experiment 2)

Treatments Da ys

Ad libitum 14 to 17 14 to 20 14 to 23 14 to 26 14 to 29 Llnenr

+ad libitum -14 to 17 * 14 to 20 -14to23 -14to26 -14to29

CHAPTER V

APPARENT ILEAL, NITROGEN DIGESTIBILITY AND APPARENT

METABOLIZABLE ENERGY CORRECTED TO ZERO NITROGEN (AMEn)

DETERMINATIONS OF STARTER, GROWER AND I?INISHER DIETS IN

BROILER CHICKENS FED DIFFERENTLY TEXTURED DIETS OR FEED-

RESTRICTED

ABSTRACT

The effect of a mild feed restriction on the apparent nitrogen digestibility in

young broiler chickens (experiment l), and the effect of textured diets and feed

restriction on the AMEn (Apparent Metabolizab le Energy corrected to zero nitrogen

retention) at different ages (experiment 2) were determined. Apparent nitrogen

digestibility and AMEn were not significantIy different (P > -05) comparing ad libitum

and feed-restricted chicks at 15 days of age. AMEn at 5 d was significantly affected (P

c -05) by the use mash diets, but not by mild feed restriction. No sirmificam

differences (P > .05) were observed in AMEn at either 28 d or 48 d comparing chicks

fed pellets, mash, or feed-restncted to 90 % of ad libitum intake of pelleted feed. It

was concluded that mild feed restriction does not influence ileal nitrogen digestibility

or AMEn in young broilers.

INTRODUCTION

The use of feed restriction programs has been considered for broiler chickens

as a means of improving feed conversion. However, it is necessary to determine if

rnild feed restriction has an effect on AMEn (Apparent Metabolizable Energy

corrected to zero nitrogen retention). Some workers have reported that resûicting feed

intake to between 30 and 90% of ad libitum intake does not affect AME (Hill and

Anderson, 1958; Bourdillon et al., 1990), while others have reported variable diet

AME related to intake (Guillaume and Srimmers, 2970; Sibbald, 1975; Kussaibati et

al., 1982; Sibbbald and Wolynetz, 1985). It is known that both fecal and urinary

energy losses depend on the amount of feed consumed. In addition, it is generaliy

accepted that feed intake levels affect classical AME values because at iow feed intake

endogenous losses represent a higher amount of energy voided in the excreta, thereby

affecting AME.

Dietary metabolizable energy is aiso affected by factors such as age (Bartov,

1988; Bartov, 1995), and the method used for evaluation (Farrell et al., 1989). It is

known that age of bird affects digestive enzyme activities and associated availability

of nutrients (Nitsan et al., 1991a; Nitsan et al., 1991b; Nir et al., 1993). Gous (1977)

suggested that in feed-restricted birds the availability of amino acids might be

increased due to irnproved absorption. Effects of feeding regimen on the activity of

digestive enzymes have also been studied by Nir et al. (1987), and Pinchasov et al.

(1990). Increased synthesis of digestive enzymes at times of feed restriction was

observed (Nir et al., 1987). Pinchasov et al. (1990) stated that the feeding regimen

afEected the activities of proteolytic e n m e s , and that the activity of trypsin was

higher in intermittent than in ad libitum fed birds. Related to this, an improved amino

acid digesti't,ility may occur in feed-restricted chicks,

In order to determine if mild feed-restriction affects nitrogen digestibility in

young broilers at 15 days of age, and if mild feed restriction or pelleting of diet

influence AMEn at different broiler ages, four experiments were camed out.

MATERIALS AND METHODS

Experiment 1

Two hundred and forty day-old male broiler chickens of a commerciaI strain

were randomly allocated to one of two treatments of 120 chicks each. Each treatment

consisted of twelve replicates of 10 birds each. Chicks were housed in an electrically

heated battery brooder and were given water ad libitum. Lighting was provided

23Wday. All birds were fed with a conventional starter diet (Diet 1, Table 5.1)

forrnulated to meet the nutrient requirernents according to the NRC (1994), ad libitum

to 5 d of age. Chromic oxide was added to the diet at a level of approximately 0.4 % as

a marker for deterrnining ileal digestibility. Chicks were fed ad libitum or feed-

restricted fiom d 9 to d 15 to 90% ad libitum intake determined £kom observations on

the control birds of the previous day.

At 15 d of age, 5 birds per replicate, selected at random, were killed by

cervical dislocation, the body cavity opened and the digestive tract imrnediately

removed. Ileal digesta was carefully removed by washing with distilled water and

gentle pressure fkom the terminal ileum (15 cm) adjacent to the ileo-cecal junction.

Digesta was pooled for the five chicks, fiom each replicate and oven-dried at 65 C for

72 hr (Hotpack, Philadelphia, PA 19154), and then allowed to come to equilibrium

with atmospheric moisture for 3 days. Digesta was ground in a commercial blender

(Warhg Products Division, New Hartford, CT 06057-0000). Nitrogen determination

was assessed in both feed and ileal digesta using a Leco nitrogen analyzer (Leco

Instruments, Stockport, Cheshire, SK7 SDA, UK). Gross energy of feed and ileal

digesta was assayed by the complete combustion of the sarnples in a CS003 IKA

adiabatic bomb cdorimeter (GMBIT and CO. KG D-79219, Staufen, Gennany),

Chromium content of the diet and digesta was anaiyzed using the method described by

Williams et al. (1962).

Statistical analysis

The experiment was arranged as a complete randomized design with replicate

as the experimental unit. Both variables were subjected to r- test procedure analysis.

(Steel et al, 1997).

Experiment 2

Starter diet

One hundred and thirty five day-old male broiler chickens of a commercial

strain were randomiy ailocated to one of ttiree treatments of 45 chicks each. Each

treatment consisted of eight replicates of 5 birds each, located in an electrically heated

battery brooder. Chicks were fed ad libitum cnimble diet (Diet 2, Table 5.1)

formuiated to meet NRC (1994) nutritional recommendations. Chicks were fed a mash

starter diet (Diet 2, Table 5-1) ad libitum, or chicks were fed the same cnrmble starter

diet but were feed-resûicted to 90% of the ad libitum intake determinations for

crumble ad libitum fed chicks of previous day. Battery brooder temperature wcts

controlled according to standard practices. Water was offered ad libitum for al1

treatments and lighting was provided 23hlday. Al1 birds had a period of adaptation of

4 d pnor to starting the excreta collection. Excreta was collected fiorn 4 - 6 d of age

and accumulated in aluminurn foil trays over 72 hr. During the excreta collection

feaihers, scales and spilled feed were removed fiom the excreta and the spilled feed

was weighed. At the end of the collection period, the excreta was wrapped in foil and

dried at 65 C for 72 hr in a forced-air oven (Hotpack, Philadelphia, PA 19154).

Samples were assayed for gross energy and nitrogen as described in Experiment 1.

AME was calculated according to Leeson et al. (1974). Correction for nitrogen

excretion was determined using 8.22 kcal/g nitrogen as described by Hill and

Anderson (1958).

Grower diet

Seventy-two 21d old male broiler chickens of a commercial strain were

randornly allocated to one of three treatments of 24 birds each. Each treatment

consisted of eight replicates of 3 birds each, located in a grower battery. Chicks were

fed ad libitum pelleted grower diet (Diet 3, Table 5.1). Chicks were fed a mash grower

diet (Diet 3, Table 5.1) ad libitum, or chicks were fed pellets but feed-restricted to

90% of ad libitum intake determinations for ad libitum fed pellets birds of previous

day. Excreta was collected fiorn 26 - 28 d of age. Subsequently the experïment

followed the same procedure as descnbed in section 2.1.

Finis her diet

Twenty-four 42 d old male broiler chickens of a commercial strain were

randomly allocated to one of three treatrnents of 8 birds each. Each treatment consisted

of eight replicates of 1 bird each, located in individually cages. Birds were placed in

alternate cages so as to prevent feed contamination. Chicks were fed a peUeted finisher

diet (Diet 4, Table 5.1) ad libitum. Chicks were fed ad libitum mash finisher diet (Diet

4, Table 5.1), or chicks were fed pellets and were feed-restricted to 90% of ad libitum

intake determinations for ad libitum fed pellet chicks of previous day. Excreta was

collected fiom 47 - 49 d of age. Subsequently sampling and andysis procedures were as

described in section 2.1.

Statistical analysis

The experiments were arranged as a complete randomized design with

replicate as the experimental unit. AU variables were andyzed by one way ANOVA.

(Steel et al, 1997).

Experiment 1

Apparent ileal nitrogen digestibility and apparent ileal metabolizable energy

(AMEn) values are shown in Table 5.2. There was no difference (P > -05) between ad

Zibirum and feed-restricted broilers at 15 days of age for either apparent nitrogen

digestibility or apparent ileal rnetabolizable energy (AMEn),

Experiment 2

AMEn of starter, grower and fïnisher diets for broiler chickens as affected by

diet texture and feed restriction is shown in Table 5.3. There were significant

differences (P < .01) in AMEn of starter diet fed as crumbles, mash, or feed-restricted

to 90% of ad libitum cnimble intake respectively (Table 5.3). No significant

differences (P > -05) were obtained in AMEn of grower or h isher diets whether fed

as pellets, mash, or feed-restricted to 90% of ad Zibitunt pellet intake respectively

(Table 5.3). AMEn values related to age and/or diet were significantly different (P c

.O 1) independent of the treatment.

DISCUSSION

The objective of these experiments was to determine if a miId feed restriction

program affects nitrogen digestibility and AMEn in broiler chickens at different ages.

Restricting the intake of young broiler chickens to 90% of ad libitum intake did not

affect apparent ileal nitrogen digestibility- This result is contrary to the results of Gous

(1977) who suggested that feed-restriction irnproves amino acid availability. Amino

acid digestibility was not determined because apparent ileal nitrogen digestibility was

not af3ected. However, it is necessary to establish if more severe feed restTiction

programs do influence nitrogen andlor amino acid digestibility.

AMEn values among birds feed-restricted to 90% of ad libitum intake and ad

libitum fed broiler chickens were not different at any age rneasured. These results are in

accord with the observations of Hill and Anderson (1958), and Bourdillon et al. (I990),

but contrary to Potter et al. (1960), who observed a slight increase in the ME of the diet

at reduced feed intake. Increased fat digestibility has been reported in growing chicks

when their feed intake is reduced (Kussaibati, 1979). However, Zelenka (1997)

suggested that AMEn decreased with increasiog feed intake, and that this is due to a

variation in ad libitum feed intake, Tt may be that no differences in AMEn between

chicks fed ad libitrtrn and feed-restrïcted to 90% of ad libitum intake resulted because

the degree of feed restriction used was not severe enough. There was a significant effect

on AMEn related to age of the birds, with increasing AMEn levels in older birds. These

results are in agreement with the observations of Bartov (1995), and Zelenka (1997).

The increased AMEn values in older birds may occur because age of birds noticeably

affects the growth of digestive organs and production of digestive enzymes, and

therefore the availability of nutrients (Nitsan et ai., 1 99 1 b; Nir et al., 1 993), andor due

to the different diets given exerts an effect. Regardless of intake level AMEn values for

cnimbles were significantly higher than for mash at 5 d old chicks. Although AMEn

values of grower and finisher diets were not significantly different at 28 and 48 days of

age regardless of texture, pelleted diets always showed higher values than those fed as

mash. This may occur due to increased digestibility of starch since pelleting causes some

gelatinization (Saunders et al., 1969), resulting in greater diet AME values.

CONCLUSIONS

There is an indication of improved AMEn due to texturing diets for young

birds, but not for older birds fed grower or fïnisher rations. Mild feed restnction does

not affect AMEn of the diet fed at any age, indicating that the level of feed restriction

applied did not reduce AMEn. It is concluded that mild feed restnction did not

improve ileal nitrogen digestibility in young chicks, therefore amino acid digestibility

is likely not irnproved.

Table 5.1. Diet composition.

Starter Grower Finisher Starter Ingredients (%)

Soybean meal (48%) Yellow corn Animal-Vegetable fat Limestone Dicalcium phosphate Salt Vitamin-mineral prernix * D ,L-Methionine Chromic oxide

Calculated analysis

ME WaV'g) 3050 3150 3190 3036 Cnide protein (%) 22.3 1 20.00 18.00 22.79 Lysine (%) 1-27 1.10 0.95 1.27 Methionine+cystine (%) 0.82 0.74 0.64 0.82 Calcium (%) 1-00 0.92 0.90 1 .O3 Available phosphorus (%) 0 -42 0.40 0.38 0.42

* Supplied per kilogram of diet: vitamin A, 8,800 IU (retinyl palmitate); cholecalciferol, 3 , 3 0 0 u vitamin E, 40 IU (dI-a-tocopheryl acetate); n'bofl avïq 8.0 mg; biotin, 0.22 mg; thiamin, 4 mg; pantothenic acid, 15.0 mg; v i d BI%, 12 ug; niacin, 50 mg; choiine, 600 mg; vitamin K, 3.3 mg; folk acid, 1.0 mg; ethoxyquin, 120 mg; manganese, 70 mg; zinc, 70 mg; copper, 10 mg; iron, 60 mg; and selenium, 0.3 mg.

Table 5.2. Feed Intake effects on apparent ileal nitrogen digestibilïty and iIeal AMEn of diets in broilers at 15 d of ape. Experiment 1.'

TREATMENT Apparent Ileal N Digestibility (%)

AMEn (kcaVkg)

Ad Libitum

Feed-restricted 1

'Pvfeans ' S E 'AME~= Apparent rnetaboIizable energy correctcd to zero nitrogen

Table 5.3. Effect of texture and feed restriction on AMEnl (Kcalkg) of starter, grower and frnisher d:

TREATMENT

ts in broiler chickens, Experiment 2.'

DIETS

TEXTURED

MASH

TE XTURED

STARTER GROWER FXNTSlAER

"b Means with different superscnpt differ significantly Pc .O 1)

CHAPTER VI

GENERAIL DISCUSSION

The objectives of the experirnents conducted in this thesis were to evaluate the

potential of mild physical feed restriction and the use of textured diets as a means of

improving feed conversion while decreasing abdominal fat content and the incidence

of rnetabolic disorders such as ascites and SDS in broiler chickens.

The use of either mild physical feed restriction or textured diets reduced

market body weight at both 42 and 49 d (Chapter III), and this is in accord with

observations of Khantaprab et al. (1997), Plavnik et al. (1997), Roth et al. (2993), and

Santoso et al. (1993a). The degree of reduction in breast meat and body weight

depended on the level of feed restriction applied, indicating that feed restriction

reduces breast muscle growth (Gille et al., 1992). It was observed that the more severe

the level of feed restriction the greater reduction in body weight and breast meat yield,

which suggests that the growth rate of broiler chickens is intimately related to feed 9

intake.

The implementation of earIy or late mild physical feed restriction at different

periods (Chapter IV) resulted in no difference in body weight compared to ad libitum

fed birds, Results suggest that the level of feed restriction allowed birds to attain

complete growth compensation. Growth compensation has been achieved by broilers

subjected to short periods of under-nutrition (Deaton, 1995; Ballay et al., 1992),

although some workers have not confirmed this concept (Pa10 et al., 1995). These

discrepancies may occur due to different levels of feed restiiction used, which

suggests that level and t h e of feed restriction is important for growth compekation.

Feed conversion was not significantly improved when broilers were subjected

to mild feed restriction fiom 5 to 42 d or fed textured diets at different growth periods

(Chapter III). This suggests that either the level of feed restriction used did not

decrease the chicks' maintenance energy needs sufficiently for an improved feed

efficiency to be realized or that the duration of feed restriction was so long that chicks

did not have time to compensate by increasing growth rate. However, when broiler

chickens were subjected to an early mild physical feed restriction (Chapter N,

Experiment 1) they showed a improved linear effect on feed conversion at 42 d with

longer period of feed restriction, agreeing with observations of Deaton (1995), and

Cristofori et al. (1997). However, th is effect did not occur when marketing birds at 49

d (Experiment 1) or restncting chicks at later ages (Chapter IV, Experiment 2), which

is in accord with resuIts of Roth et al. (1993). Improvement in feed conversion due to

feed restriction is h o w n to reduces maintenance requirements which are related to a

decrease in basal metabolic rate (Zubair and Leeson, 1994b). This situation suggests

that in order to decrease growth rate, and reduce energy maintenance requirements,

early rather than late rnild feed restriction should be applied for an extended period.

The fact that abdominal fat size was not reduced in these experiments (Chapter

III and nT) suggests that birds were 1;Jniting in amino acid intake andor were overfed

since the level of feed intake may control de novo lipogenesis (Rosebrough and

McM~uty, 1993). This is based on the suggestion of Boekholt et al. (1994) who stated

that ad libitum fed broilers are eating about 2 to 3 t h e s their maintenance energy

requirements. These results are in accord with observations of Santoso et al. (1993b),

Susbila et al. (1994), Deaton (1995), and Ramlah et al. (1996), but contrary to Plavnik

and Hururitz (2988, 1991), Pa10 et al. (1995), and Santoso et al. (1995). The

inconsistency in the results may be related to diffèrent strategies of feed restriction

used, condition of re-alimentation, age of imposition, sex, and strain of birds, which

may affect the birds' response to feed restriction. It seems that in order to reduce

abdominal fat content, more severe feed restriction throughout the birds entire life

cycle is needed.

Implementation of continuous feed restriction and use of mash diets at

different periods significantly reduced mortality across treatments. This effect was not

observed, however, when mild physical feed restriction was imposed at different

stages. This suggests that in most of the cases, mortality is related to growth rate and

hence to increased feed intake- It seems that in order to reduce the incidence of

mortality, more severe and extended per-iods than those used in Chapter N of feed

restriction are required. Moreover, mortality f?om ascites and SDS are likely related to

growth rate, high metabolic rate, and feed consumption. While these experiments were

conducted it was observed that feed restriction tended to reduce the incidence of these

disorders. A reduced incidence in these disorders h a been observed by Julia- (1997),

Tottori et al. (1997), OkSuk et al. (1998), and Gonzales et al. (1998a). The application

of feed restriction is possible an option for decreasing broiler mortality.

From the results of these experiments it can be concluded that mild physical

feed restriction is an acceptable method that allows for complete growth compensation

without affecting AMEn and nitrogen digestibility (Chapter V). Another advantage of

mild feed restriction could be that chicks achieve a more uniform growth compared to

situations involving severe under-nutrition. Early rather than Iate mild physical under-

nutrition is more advantageous due to an improvement in feed conversion and other

productive parameters. Mild physical feed restriction throughout the chick's life

reduced weight-for-age, and so extended grow-out time was needed, so while flock

economics are improved, yearly retums are reduced. Mortality was significantly

reduced when feed restriction was implemented throughout the birds' growing cycle

and when birds were fed mash diets at different penods (Chapter III), however this

effect was not as noticeable when chicks were feed-restricted for Limited time (Chapter

w- Experiments need to be conducted in restricting feed intake in broiler chickens

that are marketed at older ages. Productive parameters such as mortaliw, occurrence of

rnetabolic disorders and feed conversion need to be evduated when using continuous

mild physical feed restriction. Implementing mild physical feed restriction in older

market weight birds could alleviate the incidence of rnetabolic disorders and reduce

mortality compared to ad libitum fed chicks,

Mild physical feed restriction has the tremendous economic advantages of

improving feed conversion, reducing mortality while allowing for growth

compensation. If market body weight for age is attained, feed restriction ensures more

efficient productive parameters, and hence greater profits. It c m be concluded that the

implementation of feed restriction could be an effective and appropriate procedure in

broiler management.

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