nutritional quality of mesquite (prosopis glandulosa) …

NUTRITIONAL QUALITY OF MESQUITE (Prosopis glandulosa)

AND POTENTIAL TOXICOSIS IN SHEEP

by

RENE BAPTISTA, B ^ .

A THESIS

IN

RANGE SCIENCE

Submitted to the Graduate Faculty of Texas Tech University in

Partial Fulfillment of the Requirements for

the Degree of

MASTER OF SCIENCE

Approved

Accepted

August, 1996

j ̂ ^ ID ACKNOWLEDGEMENTS

Mo "14

I want to acknowledge Dr. Karen L. Launchbaugh, chairperson of my

committee, for allowing me to work in her mesquite project, and for her constant

support to make my studies and this thesis possible. I wish Dr. Launchbaugh

success throughout all her future plans.

I also want to express my deepest appreciation to Dr. Robert Albin for his

constructive advice and encouragement. My sincere acknowledgement to Dr.

Emilio A. Laca for his invaluable lectures during my graduate program, and for the

critical comments to improve this final document.

Special thanks to my fellow graduate students Ed Reid and Hamidou

Nantoume. I am in debt with Mike Lloyd for being so helpful during the field work.

I also want to extend my sincere gratitude to Camille Landry and Kristin

Whittenburg for their dedicated work, and for making my laboratory work easier.

Finally, I will always be grateful with my Mexican friends for being a

continuous source of support and encouragement during all this time in this friendly

country.

11

CONTENTS

ACKNOWLEDGEMENTS ii

ABSTRACT v

LIST OF TABLES vii

LIST OF FIGURES viii

CHAPTER

I. INTRODUCTION 1

Literature Cited 4

II. DIGESTIBILITY OF ALFALFA DIETS CONTAINING

VARIOUS LEVELS OF MESQUITE LEAVES 6

Abstract 6

Introduction 8

Materials and Methods 9

Results and Discussion 14

Summary and Conclusion 20

Literature Cited 23

III. GASTROINTESTINAL FEEDBACK FROM MESQUITE

ON THE INTAKE OF A NOVEL FEED 32

Abstract 32

Introduction 33 Materials and Methods 35 Results and Discussion 36

ill


Literature Cited 41

IV. SEASONAL TRENDS OF NUTRIENT COMPONENTS

OF MESQUITE LEAVES 44

Abstract 44

Introduction 45

Materials and Methods 47

Results and Discussion 49


Literature Cited 53

V. GENERAL RESEARCH CONCLUSIONS 56

APPENDIX: INTAKE OF DRY AND FRESH MESQUITE LEAVES 58

ABSTRACT

IV

ABSTRACT

Mesquite leaves are emergency forage during dry seasons but they have

low palatability. An in vivo digestion trial was completed with lambs (n = 15)

assigned to diets of 0, 5, 10, 15, or 20% mesquite leaves mixed with alfalfa hay to

measure effects of mesquite on digestion parameters. Proportion of mesquite

leaves in the diet negatively affected dry matter (DM) intake, nitrogen (N) balance,

gross energy (GE) intake, retained N, retained GE, and weight gain at levels > 5%

of the diet (P < 0.01). Mesquite intake was the highest at the 5% level (1.81 g/kg

BW; P < 0.01) and averaged 0.78 g/kg BW for the remaining diets. Coefficient of

apparent digestibility (COD) was not affected by level of mesquite in the diet (P =

0.58). An in situ Dacron bag trial revealed that pure alfalfa hay was more digestible

than mesquite leaves (P = 0.01). However, %N, acid and neutral detergent fiber

(ADF and NDF) did not differ between mesquite and alfalfa. Low levels of enzymes

bilirubin, aspartate aminotransferase, and gammaglutamyl transferase suggested

no liver damage (P > 0.05). Allelochemicals in mesquite were presumably strong

intake inhibitors.

A conditioned flavor aversion (CFA) trial tested the effect of postingestive

feedback from mesquite on the intake of a novel feed (rye). On day 1, lambs were

offered rye and then ground mesquite was infused into their rumens by tube.

Lambs (n=21) were assigned to dosing treatments 0 (control), 3.0 (low), and 4.5

(high) g/kg BW of mesquite leaves. On day 3, lambs dosed with mesquite ate less

than controls (P < 0.01) showing a strong CFA. Aversion to rye persisted for at

least 2 days (P < 0.01). The high dose of mesquite decreased the intake of alfalfa

ration for at least 3 days (P <0.01). Persistent diahrrea in lambs receiving the high

mesquite dose could be a result of toxins in mesquite.

Examination of nutrients in mesquite leaves collected from May to November

1995, showed an increasing trend for DM from 42% (May) to 58% (November).

Content of N decreased with season (P < 0.01), from a maximum of 2.73% in May

to 1.58% in November. Analysis of ADF and NDF indicated similar effect of months

(P <0.01). Minimum content of fiber was found in May, (23.7% ADF; 32.0% NDF)

and maximum levels were reached in June (32.9% ADF; 43.1% NDF). Values of

fiber decreased again in November (29% ADF; 38.8% NDF). In vitro digestibility

was similar for May and June (79%), and decreased significantly (P <0.01) for the

remaining months, from 74% in July to 69% in November.

VI

LIST OF TABLES

2.1. Crude protein (CP), in situ digestibility, neutral detergent fiber (NDF), acid detergent fiber (ADF), and gross energy (GE) for diets consisting of various proportions of mesquite leaves and alfalfa hay 25

2.2. Average lambs weight before (initial) and after (final) digestion trial on diets of mixed alfalfa and mesquite 26

2.3. Daily nitrogen balance of lambs fed diets with five levels of mesquite leaves in alfalfa hay ration 27

2.4. Effects of five levels of mesquite leaves in alfalfa diets on gross energy (GE) balance 28

2.5. Hepatic enzymes in blood serum of lambs before and after the alfalfa-mesquite digestion trial 29

3.1. Mean intake of novel feed (rye), and familiar feed (rice) by lambs before and after intraruminal dosing with ground mesquite leaves 42

3.2. Mean intake of alfalfa hay ration by lambs before and after intraruminal dosing with ground mesquite leaves 43

4.1. Seasonal variation of dry matter (DM), nitrogen (N), acid detergent fiber (ADF), neutral detergent fiber (NDF), and in vitro DM digestibility (IVDMD) in mesquite leaves 55

A.1. Average daily DM Intake (g/kg BW) of dry and fresh mesquite leaves eaten by lambs 60

Vll

LIST OF FIGURES

2.1. Average daily dry matter (DM) intake of five levels of mesquite mixed with alfalfa hay, eaten by lambs 30

2.2. Average daily dry matter (DM) intake of mesquite in diets with five levels of mesquite mixed with alfalfa hay, eaten by lambs. 30

2.3. Coefficients of apparent digestibility of five levels of mesquite mixed with alfalfa eaten by lambs 31

Vlll

CHAPTER I

INTRODUCTION

Mesquite species cover approximately 34 million hectares of rangeland in the

southwestern United States (Dahl 1982), and they are among the most predominant

invasive plants of this region. Mesquite competes for soil, light, and nutrients with

desirable forage species (Meyer et al. 1971). Honey mesquite (Prosopis

glandulosa Torr.) is the most common species of mesquite in Texas, and It infests

about 22.7 million hectares (Fisher 1977). There is evidence that mesquite was a

natural component of the desert grasslands, and that its geographical range has

changed little. The density of mesquite, however, has increased in the last 70

years (Fisher 1977), with some expansion to new areas (Gibbons et al. 1992).

Several reasons have been hypothesized for the increased mesquite density,

including droughts resulting from recent climate changes, control of natural fire, and

overgrazing (Fisher 1977). Large hervibores, including livestock, have also

contributed to the increase in mesquite by spreading seeds throughout disturbed

habitats (Janzen and Martin 1982). Mesquite possesses several characteristics

that make it a successful competitor and invasive plant, including its high tolerance

to droughts (Dahl 1984), ability to regrow after fire (Wright 1973), and hervibory

resistance (Solbrig 1977, Cates and Rhoades 1977). Therefore, from a rangeland

management standpoint, mesquite is generally considered an undesirable species

that needs to be controlled.

High densities of mesquite were related to problems with livestock

distribution and handling, and decreasing carrying capacity (Warren et al. 1996).

Decreasing carrying capacity in areas invaded by mesquite induced the investment

of significant economic and energy resources to control mesquite. Yet, 50 years

of control by mechanical, chemical, and pyric means has not significantly brought

mesquite under control (Dahl and Sosebee 1984). As mesquite control becomes

increasingly expensive (Holechek and Hess 1994), it is important to consider

potential uses and benefits of mesquite. The mesquite tree has been considered

an indispensable resource utilized by ancient human cultures providing wood, fiber,

pigments, medicines, and beans for food and beverages (Felger 1977). Moreover,

mesquite provides forage to wild herbivores, fixes atmospheric nitrogen, and brings

protection to both animals and surrounding plants (Mares et al. 1977). Scientists

have identified more than 70 potential uses mesquite, including wood, fuel, and

chemical products (Parker 1982), animal rations (Albin et al. 1976, Bryant et al.

1982), and food products (Meyer et al. 1982).

Although much is known about the nutritional quality of mesquite beans for

human and animal use (Zolfaghari et al.1982, Meyer et al. 1982), one potential

utilization rarely mentioned is the utilization of mesquite foliage as forage for

livestock. Experimental evidence suggests that mesquite foliage could constitute

about 5% of cattle diets allowing weight gains under drylot conditions

(Launchbaugh et al. 1993). Besides, mesquite is utilized by livestock and wildlife

as an emergency forage despite the potential negative effects from its

overconsumption (Stubbendieck and Conard 1989). The potential control of

mesquite with goats has been studied, suggesting the biological and economical

viability of ruminants as a tool to control mesquite (Fierro et al. 1977).

Proximal analysis suggested a nutritional quality of mesquite leaves similar

to medium quality alfalfa (Lyon et al. 1988). However, low consumption of mesquite

foliage as a forage by ruminants (Dahl 1982) indicated low palatability. Low

palatability of mesquite leaves could be attributed to its chemical defenses against

herbivores (Cates and Rhoades 1977). The possibility of increasing mesquite

utilization by domestic grazing animals deserves investigation to establish the

potential grazing management of mesquite. It is necessary to investigate the

voluntary intake and digestibility of mesquite leaves by ruminants to assess their

nutritive value. The general objective of this thesis was to assess the potential

nutritive value of mesquite. My specific objectives were:

1. To determine the digestibility, nitrogen balance, and energy balance of diets

containing mesquite leaves and to make an initial assessment of toxicity

from mesquite consumption.

2. To study the potential of gastrointestinal feedback from mesquite leaves for

creating conditioned flavor aversion.

3. To follow the seasonal changes in dry matter, crude protein, neutral

detergent fiber, and acid detergent fiber of mesquite leaves.

Literature Cited

Albin, R.C., T.E. Vernor, H.W. Parker, L.B. Sherrod,and C.B. Summers. 1976. Mesquite for ruminants. I. Effects of thermochemical treatment upon in vitro digestibility. Texas Tech Univ. Rep. 27:22.

Bryant, F.C., T. Mills, M. Carrigan, and J.S. Pitts. 1982. Ozone-treated mesquite as the roughage base in range cattle supplemental feed. p. G1-G6. In: H.W.Parker (ed.) Mesquite utilization. Symposium on mesquite utilization. Texas Tech Univ. Press, Lubbock, Tex.

Cates, R.G. and D.F. Rhoades. 1977. Prosopis leaves as a resource for insects, p. 61-83. In: B.B. Simpson (ed.) Mesquite: Its biology in two desert ecosystems. Dowden, Hutchinson & Ross, Inc., Stroudsburg, Penn.

Dahl, B.E. 1982. Mesquite as a rangeland plant p. A1-A20. In: H.W.Parker (ed.) Mesquite utilization. Symposium on mesquite utilization. Texas Tech Univ. Press, Lubbock, Tex.

Dahl, B.E. and R.E. Sosebee. 1984. Timing - the key to herbicidal control of mesquite. Texas Tech. Univ. Manage. Note. N 2.

Felger, R.S. 1977. Mesquite in Indian cultures of southwestern North America, p. 150-176. In: B.B. Simpson (ed.) Mesquite: Its biology in two desert ecosystems. Dowden, Hutchinson & Ross, Inc., Stroudsburg, Penn.

Fierro, L.C., F. Gomez, and M.H. Gonzales. 1977. Utilization of undesirable brushes by goats. (In Spanish). Grasslands Bull., Institute Nacional de Investigaciones Pecuarias, Mexico. Vol. VIII-6

Fisher, C.E. 1977. Mesquite and modern man in southwestern North America, p. 177-188. In: B.B. Simpson (ed.) Mesquite: Its biology in two desert ecosystems. Dowden, Hutchinson & Ross, Inc., Stroudsburg, Penn.

Gibbons, R.P., R.F. Beck, R.P. McNeely, and C.H. Herbel. 1992. Recent rates of mesquite establishment in the northern Chihuahuan desert. J. Range Manage. 45:585-588.

Holechek, J.L and K. Hess. 1994. Brush control considerations: A financial perspective. Rangelands 14:279-284.

Janzen, D.H. and P.S. Martin. 1982. Neotropical anachronisms: The fruit the gomphotheres ate. Science 215:19-27.

Launchbaugh, K.L., E.A. Laca, and J. Bonner. 1993. Mesquite consumption by cattle. In: Research highlights. Noxious brush and weed control. Tex. Tech Univ. Lubbock, Tex. Vol. 24:9.

Lyon, O.K., M.R. Gumbmann, and R. Becker. 1988. Value of mesquite as a forage. J. Sci. Food. Agric. 44:111-117.

Mares, M.A., F.A. Enders, J.M. Kingsolver, J.L. Neff, and B.B. Simpson. 1977. Prosopis as a niche component of plants and animals, p. 123-149. In: B.B. Simpson (ed.) Mesquite: Its biology in two desert ecosystems. Dowden, Hutchinson & Ross, Inc., Stroudsburg, Penn.

Meyer, R.E., H.L. Morton, R.H. Haas, E.D. Robison, and T.E. Riley. 1971. Morphology and anatomy of honey mesquite. Agricultural Research Service. USDA. Tech. Bull. 1423.

Meyer, D., R. Becker, and H. Neukom. 1982. Milling and separation o^ Prosopis pod components and their application in food products, p. LI-LI 2. In: H.W. Parker (ed.). Mesquite utilization. Symposium on mesquite utilization. Texas Tech Univ. Press, Lubbock, Tex.

Parker, H.W. 1982. Mesquite as a biomass residue, p. C2-C11. In: H.W. Parker (ed.). Mesquite utilization. Symposium on mesquite utilization. Texas Tech Univ. Press, Lubbock, Tex.

Stubbendieck, J. and E.C. Conard. 1989. Common legumes of the great plains. An illustrated guide. Univ. Nebr. Press., Lincoln, Nebr.

Warren, A., J. Holechek, and M. Cardenas. 1996. Honey mesquite influences on Chihuahuan desert vegetation. J. Range Manage. 49:46-52.

Wright, H.A., S.C. Bunting, and L.F. Nevenschwander. 1976. Effect of fire on honey mesquite. J. Range Manage. 29:467-471.

Zolfaghari, R., M. Harden and L. Hopkins. 1982. Nutritional value of mesquite beans (P. glandulosa). p. K1-K12. In: H.W.Parker (ed.) Mesquite utilization. Symposium on mesquite utilization. Texas Tech Univ. Press, Lubbock, Tex.

CHAPTER II

DIGESTIBILITY OF ALFALFA DIETS CONTAINING VARIOUS

LEVELS OF MESQUITE LEAVES

Abstract

Grazing management of mesquite could be viable by understanding the

effects of its chemical defenses on the digestive system of ruminants. Mesquite

leaves and pods are emergency sources of protein and energy during dry seasons

but symptoms of toxicity have been reported after their overconsumption. Low

forage value and low palatability are probably correlated to allelochemicals like

phenolics and alkaloids. Proximal analysis of mesquite leaves was similar to alfalfa

and suggested a potential nutritional value that needed to be studied. An in vivo

digestion trial was conducted to determine the effects of mesquite leaves in a mixed

alfalfa diet on dry matter (DM) intake, nitrogen (N) balance, gross energy (GE)

balance, and coefficient of apparent digestibility COD. Wether lambs (n = 15; 28.1 ±

2.6 kg initial BW) were randomly assigned to 1 of 5 diets, with 0, 5, 10, 15, or 20%

dried mesquite leaves mixed with ground alfalfa hay. Diets were offered twice daily

in a 14 days trial and feces and urine samples were collected for the last 7 days.

Diets were analyzed for N, acid and neutral detergent fiber (ADF, NDF), and GE on

DM basis. Diet digestibility was also assessed in an in situ Dacron bag trial in order

to compare with in vivo results. Potential mesquite toxicity was assessed by

analysis of liver-specific enzymes in blood as indicators of liver damage.

Nitrogen content was similar for all the diets and in situ digestibility was not

affected by levels of mesquite (P > 0.05). Yet, a t-test revealed that alfalfa hay was

more digestible than mesquite leaves (P = 0.01). ADF and NDF were similar for

both alfalfa and mesquite. GE was higher for mesquite leaves than alfalfa.

Mesquite had a negative effect on DM, N, GE intake, retained N, and retained GE

at levels > 5% of the diet (P < 0.01). Average daily DM intake was 40 and 35.7 g/kg

BW for the control and 5% mesquite levels, respectively. DM intake of diets

containing 10%, 15%, and 20% mesquite averaged 10.6, 6.3, and 3.3 g/kg BW,

respectively. Mesquite intake in mixed diets was the highest at the 5% level (1.81

g/kg BW; P < 0.01) and averaged 0.78 g/kg BW for the remaining diets. COD was

not affected by levels of dietary mesquite (P = 0.58) and no differences were found

when analyzed with DM intake as a covariate (P = 0.53). N balance was negative

for lambs offered diets with > 5% mesquite and resulted in weight loss. Lambs on

these diets had elevated N urinary excretion (P < 0.01) suggesting deamination of

body protein to meet body energy demands. Urinary GE was also higher for lambs

offered diets with > 10% mesquite. Liver specific enzymes bilirubin, aspartate

aminotransferase, and gammaglutamyl transferase indicated no liver damage (P >

0.05). Allelochemicals in mesquite were most likely strong intake inhibitors and

symptoms of negative gastrointestinal effects like diahrrea were possible indicators

of toxicity that need further study.

Introduction

Animals eat mesquite leaves and mesquite pods when other forages are in

limited supply (Lyon et al 1988., Stubbendieck and Conard 1989), and there is

experimental evidence that they can be important part of the diet of cattle

(Launchbaugh et al. 1993), and wild animals (Mares et al. 1977). However,

ingestion of large quantities of foliage may cause rumen stasis and impaction

(Stubbendieck and Conard 1989). The specific toxic compounds in mesquite have

not yet been identified, although chemical analysis of its leaves indicates a high

content of alkaloids which may affect vertebrates (Cates and Rhoades 1977).

Mesquite leaves are considered unpalatable and of low forage value (Lyon

1988). However, the reason for this low palatability is unclear because mesquite

leaves contain 16-18% crude protein and 33.6% Acid Detergent Fiber

(Launchbaugh and Laca 1993, unpublished), levels similar to mature alfalfa.

Mesquite could be a good forage if factors of low palatability and toxicity could be

identified and overcome (Launchbaugh et al. 1993). Therefore, in order to

understand why animals do not utilize mesquite as a forage and to assess its

nutritional value for ruminants, measurements of voluntary intake and digestibility

are necessary.

This chapter describes the methods I followed and the results obtained from

a conventional in vivo digestibility trial to assess intake and digestibility of diets

containing mesquite. The specific objective of this experiment was to determine the

effects of mesquite leaves In mixed alfalfa diets on dry matter (DM) intake and

8

apparent digestibility. Nitrogen and gross energy balance was also determined in

the digestion trial (Harris 1970). Potential negative effects of mesquite

allelochemicals were indirectly assessed through the analysis of liver-specific

enzymes in blood serum, as indicators of liver damage. An in situ dacron bag

digestibility trial was also performed to compare results with the in vivo trial.

Materials and Methods

In vivo digestibility was determined for mixed diets with different levels of

dried mesquite leaves and alfalfa hay by measuring differences between feed

intake and the excretion of feces and urine. Five diets were prepared with 0, 5, 10,

15, and 20% mesquite mixed with alfalfa hay. These levels were selected based

on the results of a preliminary experiment that assessed voluntary intake of

mosquito-containing diets. A medium quality alfalfa hay was selected for this study

because it has similar nitrogen (N) and fiber content as mesquite leaves

(Launchbaugh and Laca 1993, unpublished). Diets were prepared with dried

mesquite leaves, rather than fresh, based on the results of a preliminary experiment

that showed no difference in intake between fresh and dried leaves, indicating that

allelochemichals in mesquite are not volatilized in drying (Appendix A). Moreover,

dried leaves could be stored and handled more easily and changes in leaf quality

could be controlled throughout the trial. Mesquite leaves were oven dried at 55° C

for 5-7 days. Both mesquite and alfalfa hay were ground with a hammer mill (12.7

mm screen) to reduce sorting by the animals when fed.

Quality of Experimental Diets

Diets were analyzed for nitrogen (Kjeldahl; AOAC 1984) and gross energy

by bomb calorimetry (Harris 1970). Neutral Detergent Fiber (NDF) and Acid

Detergent Fiber (ADF) were determined following the filter bag technique (Komarek

et al. 1994), which is a modification of the conventional Van Soest fiber analysis

(Van Soest et al. 1991).

Four cannulated fine wool wethers (1 year old) were used to determine in situ

digestibility. Lambs were fed with an alfalfa hay basal ration with 5% mesquite for

15 days before beginning the experiment. Six levels of mesquite, 0, 5, 10, 15, 20,

and 100 % mesquite were mixed with alfalfa hay. Mesquite and alfalfa samples

were ground separately in a Wiley mill to pass through a 2 mm screen.

I prepared 12 bags (2 bags/treatment) for each sheep. Bags were 60 // mesh

and 10 X 5 cm. Alfalfa-mesquite samples were weighed to 8 g and were placed in

the bags. Each Dacron bag was identified (animal and treatment) with a permanent

marker and tied tightly with a nylon fishing line. Ten cm of nylon line was left to

attach each bag to the remaining bags. Two colored glass marbles were placed in

each bag for weight to draw the bag into the rumen liquor when placed in the

rumen. The prepared bags were weighed and dried overnight at 60° C to obtain the

initial DM weight. The Dacron bags were connected to a double piece of fishing

line, presoaked in water, and inserted in the rumen cannula for 48 hours. Each set

of bags was tied to a 5 cm plastic ring placed outside the cannula to prevent losing

samples inside the rumen.

10

After 48 hours, the bags were recovered and cleaned with tap water. When

water ran clear after dipping the bags, they were oven dried for 24 hours and

weighed to obtain final undigested dry matter. The formula to calculate in situ dry

matter digestibility was:

IN SITUD\Q% = initialbagwt-finalbagwt ^^^^ sampleg(DM)

Digestion Trial

Fifteen fine wool wether lambs (8-9 months old) from a ranch in Eastern New

Mexico were used. Animals were weighed after fasting 12 hours on the first and

last days of the trial collection period. The average initial weight of lambs was

28.1± 2.6 kg. Ten days before the collection period, lambs were placed,

individually, in 1.5 x 2 m wire pens. Animals were randomly assigned to 5 diets and

given ad libitum access to feed twice daily (0800 and 1800). Uneaten feed was

removed and replaced with freshly prepared food at each feeding.

Lambs were placed in metabolism crates 5 days before the experimental

collection period to allow acclimation to the crates. Treatment diets were offered

twice daily (800 and 1800) and feces and urine were collected each day (1700)

during the collection period of 7 days.

Feces were weighed and a 20% aliquot was pooled and frozen by individual

with other daily samples. At the end of the collection period, the total fecal sample

from each animal was weighed, mixed thoroughly and a 400 g subsample was

taken. Subsamples were dried at 55°C and ground to pass through a 1 mm screen

11

for subsequent chemical analysis. Feces were analyzed for nitrogen (N) and gross

energy (GE) content using macro Kjeldahl (AOAC 1984) and bomb calorimetry

procedures (Harris 1970).

Total urine output was measured for each animal and samples (10% of

volume) were composited, labeled, and refrigerated daily. To each urine collection

container, 200 ml of 0.1 N HCL was added to avoid volatilization of ammonia

(Schneider and Flatt 1975). For total output less than 1,000 ml/day, samples (10%)

were diluted to 100 ml with distilled water. At the end of the collection period, 400

ml subsamples of pooled urine samples were taken and frozen for chemical

analysis. Analysis of urine included N by macro Kjeldahl (AOAC 1984) and gross

energy by bomb calorimetry (Harris 1970). In preparation for bomb calorimeter,

urine samples (100 ml) were filtered into glass beakers, frozen and then freeze

dried. Beakers and urine samples were weighed before and after freeze drying to

determine % dry matter. Samples were freeze dried for 4 days, and then the

residue was weighed and made into pellets for bomb calorimetry. Pellets, weighing

0.3 to 0.5 g, were maintained in freeze drier to ensure dryness for bomb calorimetry

(Paladines et al. 1963).

Blood samples were taken on the first day of the adaptation period via

jugular vein puncture, to establish a baseline for determinations of liver-specific

enzymes in blood serum as indicators of liver damage (Plaa and Charbonneau

1994). Liver-specific enzymes bilirubin (BILI), aspartate aminotransferase (AST),

and gamma glutamyltransferase (GGT) in blood serum were examined. A second

12

set of blood samples was collected on the last day of the collection period to

examine changes in enzyme levels for indications of mesquite toxicosis. Blood

samples were analyzed at the Texas Veterinary Medical Diagnostic Laboratory,

Amarillo, TX.

Digestion Parameter Estimates

On the basis of the chemical analysis of feed, orts, feces and urine, I

determined the coefficient of apparent digestibility (COD), retained nitrogen, and

retained gross energy for lambs on various alfalfa-mesquite diets. The following

equations were used:

^^rs n/ nutrient In feed - nutrient In feces . . . COD % = x 1 GO nutrient in feed

RETAINED N = I - (U+F)

where, I = total g of N ingested (fed - orts); U=total g of N excreted in urine;

F= total g of N excreted in feces.

RETAINEDGE % = ° ^ '"'̂ '̂ ^ " ^^ '" ^''" " ° ^ '" " '̂"" X 100. GE intake

Experimental Design

The in vivo digestion trial was a complete randomized design with DM intake

tested as a covariate. Animals (n=15) were randomly assigned to 1 of 5 diets: 0,

5, 10, 15, or 20% dried mesquite leaves in alfalfa hay, as fed. SYSTAT for

13

Windows (1992) and SAS (1996), statistical packages were used to analyze the

data. Data that did not follow a normal distribution or did not have homogenous

variances were log or 1/x transformed before analysis (Steel and Torrie 1960).

Mean separation was performed using Fisher protected LSD procedure with 0.05

alpha-level.

Results and Discussion

Quality of Experimental Diets

Crude protein of treatment diets was not affected by increasing levels of

mesquite (P = 0.88; Table 2.1). Crude protein (CP = N x 6.25) was calculated from

N content of the diets. However, a high proportion of the N in mesquite may consist

of non-protein nitrogenated compounds, like non-protein amino acids, alkaloids,

and other defensive chemicals (Solbrig et al. 1977). Thus, "crude protein" may be

a misleading term in this case.

The proportion of mesquite in diet (0 - 20%) did not affect in situ digestibility

(P = 0.08). However, a t-test comparing in situ digestibility values of alfalfa hay (0%

mesquite), and mesquite leaves (100% mesquite) revealed a higher digestiblity of

alfalfa hay (P < 0.01; mean difference was 0.09 and value of t = 18.154 ).

Neutral Detergent Fiber (NDF), and Acid Detergent Fiber (ADF) results were

variable. There was no clear trend or relationship between increasing proportions

of mesquite and decreasing proportions of alfalfa. These parameters seemed to

reveal problems of heterogeneity in the diet samples, or interactions between

14

secondary compounds in mesquite and intermediate chemical processes for NDF

and ADF determinations (Table 2.1). Gross energy had a positive correlation with

increasing amounts of mesquite in diet. The 100% mesquite control had clearly

more energy (cal/g) than the alfalfa control (0% mesquite level) (Table 2.1).

Voluntary Intake

Mesquite leaves added to an alfalfa diet had a marked negative effect on DM

Intake (P < 0.01; Fig.2.1a). Lambs that ate 5% mesquite did not have reduced total

intake over lambs eating pure alfalfa. However, animals that were offered 10 %

mesquite or more, decreased intake drastically, compared to controls (P < 0.01; Fig.

2.1). Low levels of intake associated with mesquite contents greater than 5% in the

ration could be attributable to the effect of plant allelochemicals. The feeding

behavior (i.e., voluntary intake) of herbivorous mammals is dependent on their

detoxification capacity (Freeland 1991), thus the level of mesquite in the diet may

have set an upper limit to the total daily intake. Presumably, toxin concentration

was minimum at 5% mesquite diet and, therefore, allowed the maximum nutrient

intake with the least toxin intake (Belovsky and Schmitz 1991). However, if the

intake of mesquite containing diets was set by the maximum amount of mesquite

a lamb could process and detoxify in a day, then the total daily intake of mesquite

should be the same for all sheep, regardless of % of mesquite in the diet. This was

not the case (P< 0.01; Fig. 2.2.). Lambs offered diets of 10, 15, and 20% mesquite

ate an average of 0.78 g/kg BW of mesquite. However, lambs offered diets with 5%

15

mesquite ate 1.81 g/kg BW mesquite daily (Fig. 2.2.). Lambs may have been more

able to detoxify and digest the dietary mesquite at 5% level because they had

greater energy and nutrient intake from the greater proportion of alfalfa in their

diets. Additional nutrient and energy resources can often enhance an animal's

ability to detoxify allelochemicals in plants (Launchbaugh 1996).

Allelochemicals or defensive compounds in plants are known to limit the

nutritive value of many plants and can have various biological effects, such as

interfering with the animal metabolism or inhibiting rumen microbial activity

(Provenza 1995). The main groups of defensive compounds identified in mesquite

leaves are flavonoids, and non-protein amino acids which may have antiherbivory

properties (Solbrig et al. 1977). Other allelochemicals identified In Prosopis leaves

include phenolics (Lyon 1988) and alkaloids (Cates and Rhoades 1977). Alkaloids

are nitrogenous compounds than can exhibit pharmacological effects or inhibit

digestion (Van Soest 1994) or can be correlated to low preference by grazing

animals (Minson 1990). The animal response to defensive compounds of mesquite

in this experiment, agreed with the general feeding strategy of herbivores; that Is

to minimize the ingestion of defensive compounds (Cates and Rhoades 1977).

Specific identification of mesquite allelochemicals was beyond the scope of this

study.

16

Coefficient of Digestibility (non)

COD did not differ among treatments (P = 0.58, Fig. 2.3) suggesting that

relative digestibility was not affected and the major effect of adding mesquite to the

diet was depression of intake (Fig. 2.1). Although decreased intake often results

in higher digestibility of feeds (Van Soest 1994), no differences in digestibility were

found when DM intake was accounted for as a covariate (P= 0.75). This lack of

effect of mesquite on digestibility was similar to that observed in the in situ digestion

trial. However, the in situ technique yielded apparently higher digestibility than the

in vivo method. This may have resulted from residency times less than 48 hrs. in

the in vivo trial, whereas in situ bags were left in the rumen for 48 hrs.

Changes in Live Weight

Low intake of diets with more than 5% mesquite resulted in weight loss for

lambs assigned to those treatments (Table 2.2). Only diets with 0%, and 5%

mesquite resulted in weight gain and did not differ statistically. Note that animals

that ate the highest total amount of mesquite (5% mesquite in diet) gained weight,

suggesting requirements of energy and nutrients for detoxication metabolism were

adequate.

Nitrogen Balance

Nitrogen intake was negatively affected by levels of mesquite in rations

higher than 5% (P < 0.01; Table 2.3), following a pattern similar to the voluntary DM

17

intake. Mesquite had a strong effect on N retention at levels higher than 5% in the

diet (P < 0.01; Table 2.3). Retained N for lambs eating diets of 0% and 5%

mesquite was very low but similar, indicating protein levels close to maintenance

requirements. Lambs eating diets with 10% mesquite had lower retained N than

controls, but not different from lambs eating 5% and 15% dietary mesquite (P >

0.05; Table 2.3). However, lambs eating diets with 5% had higher retained N than

those eating diets with 15% mesquite (P < 0.01; Table 2.3). Lambs eating diets

with 20% mesquite had the lowest retained N (P < 0.01; Table 2.3).

When retained N was expressed as a percent of N intake, results showed

significant differences among treatments (P=0.01; Table 2.3). Lambs eating diets

with 0 or 5% mesquite had similar and positive retained N, as a % of N intake.

Results of N retention for lambs eating diets with more than 5% mesquite were

negative, indicating catabolism of body proteins and weight loss. Nitrogen retention

ranged between -45.5% and -47.1% of the total N ingested.

Total output of N was similar for lambs eating diets of 0% and 5% mesquite,

but differed markedly from levels of mesquite higher than 5% (P < 0.01; Table 2.3).

Nitrogen output in urine, when expressed as a percentage of total output, increased

at levels of dietary mesquite higher than 5% (P = 0.01; Table 2.3). Fecal N,

expressed as a percentage of total output, followed an inverse trend when

compared to the urinary N. Mesquite levels higher than 5% in diet increased the

proportion of urinary N (P = 0.01; Table 2.3), suggesting a process of muscle

deamination to obtain energy for the basal metabolism (Maynard et al. 1979).

18

Gross Energy Balance

Total intake of gross energy (GE) was negatively related to the mesquite

level in the diet (P < 0.01; Table 2.4). GE intake was similar for lambs eating diets

with 0% and 5% mesquite, but began to decrease sharply when 10% or more

mesquite was added to the diet. Mesquite in treatment diets also strongly affected

retained energy (P < 0.01; Table 2.4). However, when retained GE was expressed

as a % of intake, there was no difference between treatments (P= 0.50; Table 2.4).

This indicates that GE was equally digestible in all diets.

Total output of GE was significantly affected by level of mesquite in diets

(P<0.01; Table 2.4). Lambs assigned to 0% and 5% dietary mesquite showed no

significant differences in GE output. But, GE output of animals assigned to levels

of mesquite greater than 5% differed from one another with animals eating diets

with 20% mesquite having the lowest GE output (P < 0.02; Table 2.4). Fecal and

urinary GE were analyzed as a percentage of total output and both were affected

by mesquite in diets (P < 0.01; Table 2.4). Fecal GE, expressed as a % of output,

was the same for lambs eating 0, 5, and 10% mesquite but was depressed by diets

with 15% and 20% mesquite. Urinary GE, expressed as a percent of total output,

followed the inverse trend, with an increase in GE for diets containing more than

10% mesquite (P < 0.01; Table 2.4). Increased GE urinary output may have been

related to an increase in products of catabolism, such as nitrogenous compounds,

being concentrated in the urine (Maynard et al. 1979).

19

Liver Damage

Liver-specific enzymes, bilirubin (BILI), aspartate aminotransferase (AST),

and gamma glutamyltransferase (GGT) in blood serum were compared from

samples taken before and after the digestion trial (Table 2.5.) Statistical

comparison of BILI, AST, and GGT enzymes levels before and after the trial

showed no difference among treatments (P > 0.05). These results indicated that

liver necrosis did not result from mesquite consumption. Lambs on high levels of

mesquite expressed variable symptoms of constipation and diahrrea, indicating a

negative effect of mesquite on digestion. Therefore, it will be necessary to explore

other toxic effects related to intake depression and gastrointestinal illness.

Summary and Conclusion

Mesquite leaves added at increasing levels to alfalfa hay did not change

basic parameters of nutritional quality of the diet as measured by laboratory

methods. Chemical composition of mesquite leaves was similar to alfalfa when

analyzed for CP, ADF, and NDF. The in situ digestibility was not different in the

range from 0 to 20% mesquite; however, a t-test revealed that pure mesquite was

less digestible than alfalfa (60 to 69%, respectively).

In the digestion trial, lambs offered diets with 5% mesquite had similar weight

gain and intake as lambs offered 100% alfalfa diets. Levels of mesquite higher than

5% in the diet decreased voluntary intake and caused weight loss in all the animals.

Average voluntary intake of Iambs fed with diets higher than 5% mesquite was 26.5

20

% of the control intake for the 10% mesquite diet, and was only 8.3% of the control

intake at the 20% mesquite diet.

Apparent DM digestibility was not affected by increasing levels of mesquite.

However, when considering expected higher digestibilities for lower amounts of

intake, mesquite may have had a detrimental effect on digestibility. Nitrogen

balance showed negative values for all the lambs fed diets of 10% to 20%

mesquite. Mesquite levels higher than 5% in the diet decreased fecal N and

increased urinary N. Significant high levels of urinary N suggested deamination of

protein as an alternative source of energy for lambs with below-maintenance levels

of protein and energy intake (Maynard et al. 1979). Higher values of gross energy

(GE) in mesquite than alfalfa increased total GE in diets but decreased GE intake

at levels of mesquite > 5%. Digestible energy, however, remained the same for all

the levels of mesquite in the diet.

Potential toxicity, measured by the presence of liver-specific enzymes in

blood, was not affected by mesquite. These preliminary results suggested no liver

necrosis as a result of mesquite consumption. However, more detailed analysis of

liver activity is necessary to assess mesquite effects on the liver. The strong effect

of mesquite on intake, and observed diarrhea for lambs eating diets with more than

5% mesquite, were evidence of toxic effects.

In general terms, diets containing 5% mesquite did not have detrimental

effect on animals and this level appeared to agree with other experimental evidence

that supported such limit for cattle (Launchbaugh et al. 1993). However, there is

21

evidence of variation between different breeds and between groups of animals with

different dietary experience, and wide variation among individuals as well. This was

the case when a group of crossbred lambs raised under drylot conditions ate as

much as 300% more mesquite than a group of fine wool lambs with grazing

experience (Baptista and Launchbaugh 1995). Individuals with high tolerance to

mesquite in their diets were not rare, and this variation may be useful in range

management through the selection of animals with high tolerance to the toxic

compounds of mesquite.

The main effect of mesquite on lambs in my study was a strong effect on

intake. Therefore, there are probably one or several allelochemicals in mesquite

that act as powerful feeding deterrents. Research is needed to identify the specific

chemicals that make mesquite unpalatable and the mechanisms by which these

chemicals affect the animal. Understanding these mechanisms of unpalatability

could lead to viable grazing management of mesquite.

22

Literature Cited

AOAC. 1984. Official methods of analysis. (14th Ed). Assoc, of Official Analytical Chem., Washington, D.C.

Baptista, R. and KL. Launchbaugh. 1995. Intake of mesquite leaves by sheep. In: Research Highlights 1995. Noxious Brush and Weed ControL College of Ag. Sc. and Nat. Resources. Texas Tech Univ. Lubbock, Tex. 26:25.

Belovsky, G.E. and O.J. Schmitz. 1991. Mammalian herbivore optimal foraging and the role of plant defenses, p. 1-28. In: R.T. Palo, and C.T. Robbins (eds.). Plant defenses against mammalian herbivory. CRC Press, Inc., Boca Raton, Fla.

Cates, R.G.and D.F. Rhoades. 1977. Prosopis leaves as a resource for insects, p. 61-83. In: B.B. Simpson (ed.), Mesquite: Its biology in two desert ecosystems. Dowden, Hutchinson & Ross, Inc., Stroudsburg, Penn.

Freeland, W.J. 1991. Plant secondary metabolites. Biochemical coevolution with herbivores, p. 61-81. In: R.T. Palo, and C.T. Robbins (eds.). Plant defenses against mammalian herbivory. CRC Press, Inc., Boca Raton, Fla.

Harris, L.E. 1970. Nutrition research techniques for domestic and wild animals. Vol.1. Utah State Univ. Logan, Ut

Komarek, A.R., J.B. Robertson, and P.J. Van Soest 1994. A comparison of methods for determining ADF using the filter bag technique versus conventional filtration. J. Dairy Sc. 77: Suppl. 1.

Launchbaugh, K.L. 1966. Biochemical aspects of grazing behavior, p. 159-184. In: J. Hodgson, and A.W. lllius (eds.), The ecology and management of grazing systems. CAB International, Wallingford, U.K. (in press).

Launchbaugh, K.L., E.A. Laca and J. Bonner. 1993. Mesquite consumption by cattle. In: Research Highlights 1993. Noxious Brush and Weed Control. CollegeofAg. Sc. and Nat Resources. Texas Tech Univ. Lubbock, Tex. 24:9.

Lyon, C.K, M.R. Gumbmann, and R. Becker. 1988. Value of mesquite leaves as ' forage. J. Sci. Food. Agric. 44:111-117.

23

Mares, M.A.. F.A. Enders, J.M. Kingsolver, J.L. Neff, and B.B. Simpson. 1977. Prosopis as a niche component, p. 123-149. In: B.B. Simpson (ed.), Mesquite: Its biology in two desert ecosystems. Dowden, Hutchinson & Ross, Inc., Stroudsburg, Penn.

Minson, D.J. 1990. Forage in ruminant nutrition. Academic Press, Inc., San Diego, Ca.

Paladines, O.L, J.T. Reid, B.D.H. Van Niekerk, and A. Bensadoun. 1963. Relationship between the nitrogen content and the heat of combustion value of sheep urine. J. An. Sc. 23:528-532.

Plaa, G.L, and M. Charbonneau. 1994. Detection and evaluation of chemically induced liver injury, p. 839-870. In: A. Wallace Hayes (ed.). Principles and methods of toxicology. (3rd Ed). Raven Press. Ltd. New York, N.Y.

Provenza, F.D. 1995. Postingestive feedback as an elementary determinant of food preference and intake in ruminants. J. Range Manage. 48: 2-17.

SAS. 1996. Statistical analysis system. Ver. 6.09. Gary, N.C.

Schneider, B. H. and W. P. Flatt. 1975. The evaluation of feeds through digestibility experiments. Univ. of Georgia Press, Athens. GA

Solbrig, O.T., K. Bawa, N.J. Carman, J.H. Hunziker, CA. Naranjo, R.A. Palacios, L. Poggio, and B.B. Simpson. 1977. p. 44-60. Patterns of variation. In: B.B. Simpson (ed). Mesquite: Its biology in two desert ecosystems. Dowden, Hutchinson & Ross, Inc. Stroudsburg, Penn.

Steel, R.G.D. and J.H. Torrie. 1960. Principles and procedures of statistics. McGraw-Hill Book Company, Inc., N.Y.

Stubbendieck, J. and E.C. Conard. 1989. Common legumes of the great plains: An illustrated guide. Univ. of Nebraska Press. Lincoln, Neb.

SYSTAT. 1992. Systat for windows: statistics. Version 5 Ed. Evanston, III.

Van Soest, P.J., J.B. Robertson, and B.A. Lewis. 1991. Methods for dietary fiber, neutral detergent fiber and non-starch polysaccharides in relation to animal nutrition. J. Dairy Sci. 74: 3583-3597.

Van Soest, P. J. 1994. Nutritional ecology of the ruminant. Cornell University Press, Ithaca, N.Y.

24

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Weight (kg)

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Final

Difference

0

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26

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20

Figure 2.2. Average daily dry matter (DM) intake of mesquite in diets of with five levels of mesquite mixed with alfalfa hay eaten by lambs. Vertical lines on bars indicate standard errors, and same letters on bars mean no difference between treatments (P > 0.05).

30

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20

Figure 2.3. Coefficients of digestibility of five levels of mesquite mixed with alfalfa eaten by lambs. Vertical lines on bars indicate standard errors

31

CHAPTER III

GASTROINTESTINAL FEEDBACK FROM MESQUITE ON

THE INTAKE OF A NOVEL FEED

Abstract

Low voluntary intake of mesquite leaves from the in vivo digestibility trial

(Chapter II) did not explain clearly if low palatability could be attributed to an

Inherent aversive flavor or a to a postingestive effect. Therefore, I examined the

role of gastrointestinal feedback from mesquite on intake. A conditioned flavor

aversion (CFA) tested the effect of postingestive feedback from mesquite on the

intake of a novel palatable feed. Lambs (n=21) were randomly assigned to 3

treatments, 0 (control), 3.0 (low), and 4.5 (high) g/kg BW of mesquite leaves.

Treatments were prepared with ground dried mesquite leaves (0.5 mm screen,

Wiley mill) mixed with 1.5 I of distilled water. Novel and familiar feeds were offered

in the morning and an alfalfa hay ration (2% BW) was offered in the afternoon to

meet minimum nutrient requirements. On day 1, lambs were offered a novel feed

(rye 300 g) for 30 minutes and then mesquite was infused into their rumens by tube.

Control animals were dosed with water only. All lambs ate similar amounts of rye

before dosing (P=0.99). On day 2, lambs were offered a familiar feed (barley). The

consumption of barley was not affected by mesquite dose (P = 0.30). On day 3, the

formation of a CFA was tested by offering lambs rye (250 g) again; lambs that were

dosed with mesquite ate less than controls (P < 0.01) indicating a strong CFA. A

32

familiar feed (rice 200 g) was offered on the same day to examine general appetite

for grains and revealed no effect of mesquite dose on intake of rice (P=0.23). On

day 4. lambs were again offered rye (300 g), and revealed that the CFA to rye

persisted for at least 2 days (P < 0.01).

Alfalfa intake of the 3 groups was also monitored and revealed that a high

dose of mesquite decreased the intake of alfalfa for at least 3 days (P<0.01). The

observation of persistent diahrrea in lambs receiving the high mesquite dose also

indicated that the toxic allelochemicals in mesquite are presumably detrimental to

the digestive system at high doses. High tolerance to mesquite dosing was

observed on some lambs.

Introduction

There is experimental evidence that diet selection by ruminants is

determined by interactions between the senses (i.e., taste and smell) and the

consequences of food ingestion, such as satiety or malaise. This model suggests

that diet selection is a consequence of positive or negative feedback and involves

a learning process (Provenza et al. 1992). The learning model also can explain

how feedback from nutrients and toxins allows animals to select nutritious foods

and limit intake of toxic foods (Provenza et al. 1992, Provenza 1995).

Defensive compounds in plants strongly influence the diet selection of large

herbivores (Freeland and Janzen 1974. Provenza et al. 1990). Aversive

postingestive feedback and a consequent decrease in intake have been reported

33

after ingestion of toxic plants (Provenza et al. 1990). and specific toxic compounds

like lithium chloride (du Toit et al. 1991. Launchbaugh et al. 1993). Additionally,

stronger aversions are formed with increasing severity of illness (du Toit et al.

1991).

Mesquite leaves are unpalatable and negatively affect intake, but the role of

aversive flavor and postingestive feedback remained unclear (Chapter II). Because

much experimental evidence suggests that ruminants learn to avoid toxicosis

through postingestive feedback (Provenza et al. 1990). I conducted an experiment

to test aversive postingestive feedback from mesquite intake. Aversive

postingestive feedback causes ruminants to decrease intake of toxic foods

(Provenza 1995). However, when whole plants are examined, both flavor and

feedback influence intake. Therefore, I proposed to study the intake of a novel feed

under increasing doses of mesquite leaves delivered directly to the rumen.

A method for testing conditioned flavor aversions (CFA) was described by

Provenza et al. (1990), and consists of offering a novel food (rye grain in my

experiment) for a short time, then infusing a potential toxicant (mesquite leaves) into

the rumen after intake of the novel food. A CFA to the novel food is expected if the

toxicant causes negative gastrointestinal consequences.

The general objective of my study was to separate pre-ingestive from post

ingestive effects of mesquite. The specific objective of this experiment was to

examine the effect of mesquite on the formation of a CFA to a novel palatable feed.

34

Materials and MpthnHc

Twenty-one crossbred fine-wool lambs (1 year old), previously utilized in a

digestion trial, were placed in individual pens (1.5 x 2 m) and fed a basal ration of

ground alfalfa hay (2% BW per day). Water and trace mineral salt were offered ad

libitum.

Adjustment Period

Novel feeds were offered before the trial to familiarize the lambs with the

frequent presentation of new feeds. Three novel feeds (300 g/day) were offered for

fifteen minutes per day, each one for 1 to 3 days, according to the level of intake.

Novel foods were soybean meal, crimped barley, and oregano-flavored rice (1%

oregano) offered for 3, 2, and 1 day, respectively. Intake of bartey and rice was

high enough to allow a different novel feed in fewer days.

Experimental Period

On the seventh day. lambs were offered a novel feed, rye grain (300 g), and

mesquite was infused trough a flexible tube into the lamb's rumen. Rye was placed

in feed boxes for 30 minutes (at 0900) and intake was measured. Infusing mesquite

began immediately after consumption of rye. Lambs were randomly assigned to 1

of 3 treatments and dosed with 0, 3.0, or 4.5 g of mesquite per kg BW. Mesquite

was ground to pass through a 0.5 mm screen and mixed with 1.5 I of distilled water

for infusing. Control animals were dosed with water only. On the day after dosing,

35

lambs were fed a familiar feed, bartey (300 g). and the ration of alfalfa to allow

recovery. On day 3. lambs were offered rye again to test for a CFA induced by

mesquite. A familiar feed, rice (200 g), was offered after rye to assess effects of

dosing on appetite. Intake of the alfalfa ration was also measured before and after

dosing to understand potential negative effects of mesquite on appetite and

gastrointestinal function.

Experimental Design

Intake of novel and familiar feeds was analyzed as a completely randomized

design. Persistence of CFA and Intake of the alfalfa ration were examined over

time with repeated measures (SAS 1996). Differences between means were

determined using Fisher's protected LSD. Although many CFA data had non-

normal distributions, they were analyzed with robust parametnc procedures after

testing for homogeneity of vanances.


Dosing Day and Rest Dav (Davs 1 and 2)

On day 1 of the tnal. the three groups (0. 3. and 4.5 g mesquite/kg BW)

ingested similar amounts of the novel feed, rye (P = 0.99; Table 3.1). The animals

were then dosed with mesquite. On day 2, the consumption of the familiar feed

bartey (300 g). was not affected by the dose of infused mesquite (P = 0.30). Lambs

that received no mesquite ate 271.4±42.4 g of bartey, lambs that received 3.0 g/kg

36

BW of mesquite ate 181.7±76.1 g of bartey and lambs that received 4.5 g/kg BW

of mesquite ate 208.7±62.5 g of bartey on the day following dosing. This indicated

no significant effect of mesquite dosing on intake of familiar feed 24 hours after

dosing.

CFA Test (Dav 3̂

On day 3. Lambs from both mesquite treatments ate less than the control

group (P < 0.01; Table 3.1). Mean separation revealed no differences in the

amount of rye eaten between lambs dosed with 3.0 and 4.5 g/kg BW. This

indicated that mesquite dosing after intake of a novel feed created a strong CFA to

the novel feed. On the same day 3. intake of a familiar feed, nee (200 g),

immediately after consumption of rye. was similar among the three groups of lambs

(P = 0.23). Thus, the low rye intake by lambs dosed with mesquite was not due to

a general loss of appetite for all grains; but rather, a specific aversion to rye.

CFA Persistence Test (Dav 4)

On day 4. persistence of the CFA to rye was tested by again offering rye

(300 g) to lambs. Mean intake of rye for both doses of mesquite 3.0 and 4.5 g/kg

BWwas higher (52.7 g and 109.2 g. respectively) than on day 3 (22.4 g and 52.1

g. respectively). Lambs dosed with mesquite increased significantly their intake on

day 4 (P <0.01). as a probable result of gradual extinction of an aversion. However,

intake between day 1 (before mesquite infusion) and day 4 were still significantly

37

different (P <0.05; Table 3.1). Response of lambs to mesquite treatments was not

different between mesquite doses (P > 0.05) and both were different from the

control group (P < 0.01; Table 3.1).

Alfalfa Ration Intake

Comparison of alfalfa ration intake by all lambs before and for three days

after dosing showed a vanable pattern with some animals apparently less affected

by the mesquite dosing than others. After dosing, lambs receiving the highest dose

(4.5 g/kg BW mesquite) ate less alfalfa than lambs in the control and low mesquite

dose groups and less than they had before dosing (P < 0.01). After two days,

lambs receiving the high dose of mesquite increased their average intake slightly

(from 8.6 g/kg BW to 12.1 kg BW; Table 3.2) but still ate less than other lambs.

These results suggest a toxic effect of mesquite allelochemicals at the high dose.

Lambs infused with 4.5 g/kg mesquite showed clear symptoms of gastrointestinal

distress. Only 2 lambs with the low dose showed symptoms of diarrhea and they

recovered completely by the last day of the trtal. Of lambs receiving the high

mesquite dose, 4 (out of 6) showed symptoms of diahrrea and depression until the

last day of the trial. This suggested either a created aversion to the familiar basal

ration, alfalfa, or a general loss of appetite that resulted in lower consumption of the

basal ration. Variation in individual intake suggested some lambs may be more

tolerant or more efficient at detoxifying mesquite allelochemicals than others (Table

3.2).

38


The formation of a strong CFA to a novel feed after infusion of mesquite was

evidence of negative postingestive effect from mesquite leaves. This suggested

palatability of mesquite is influenced by postingestive feedback although an

inherent aversive taste may also play a role (Provenza et al. 1990). The

concentration of allelochemicals in mesquite probably played a major role in the

grade of response and persistence of CFA (du Toit 1991. Launchbaugh 1993 ).

The minimum amount of mesquite necessary to form a CFA in sheep may probably

be between 1.8 g/kg BW and 3.0 g/kg BW, under maintenance nutritional levels,

based on levels of intake in Chapter II.

On the CFA test day, lambs from the low and high dose of mesquite (3.0 and

4.5 g/kg BW) ate significantly less novel feed (rye) than the control group (0 g/kg

BW). thus indicating a strong CFA. Intake of another familiar feed (rice) on the

same day revealed that mesquite did not affect appetite for grains. CFA

persistence, tested on day 4, showed that lambs ate more on day 4 than on day 3

(P < 0.01). but the high dose group still ate significantly less than the control group

(table 1). Thus, the persistence of CFA after three days of infusing mesquite

suggested strong effect of mesquite allelochemicals at high dose.

Intake of alfalfa hay ration was also affected by mesquite dosing. When

comparing intake of the three groups before and after mesquite dosing, results

analyzed over time revealed a highly significant effect of mesquite on dosed

groups, and significant differences between days when compared to the baseline

39

day (before mesquite infusion). Symptoms of diahrrea and depression on lambs

infused with mesquite were more severe and lasted longer in lambs Infused with

high dose of mesquite.

Observation of individuals with high tolerance to mesquite and identification

of individuals with high susceptibility to low dose of mesquite confirmed high

variation in animal groups that needs to be studied. Animals that formed only weak

aversions to rye may possess a greater ability to detoxify mesquite allelochemicals

or a greater tolerance of these chemicals. Understanding these mechanisms of

detoxification or tolerance may explain differences in the voluntary intake of

mesquite (Chapter II) and may one day lead to ways to increase the consumption

of mesquite by livestock.

40

Literature Cited

du Toit, J.T., Provenza, F.D. and A.S. Nastis. 1991. Conditioned food aversions: How sick must a ruminant get before it detects toxicity In foods? Appl. Anim. Behav. Sci. 30:35-46.

Freeland, W.J. and D.H. Janzen. 1974. Strategies of herbivory by mammals: the role of plant secondary compounds. Am. NaL 108: 269-289.

Launchbaugh, K.L., F.D. Provenza and E.A. BurriL 1993. How herbivores track variable environments: Response to variability of phytotoxins. J. Chem. Ecol. 19:1047-1056.

Provenza. F.D. 1995. Postingestive feedback as an elementary determinant of food preference and intake in ruminants. J. Range Manage. 48: 2-17.

Provenza. F.D. . E.A. Burrit, T.P. Clausen. J.P. Bryant. P.B. Reichardt. and R.A. Distel. 1990. Conditioned flavor aversion: a mechanism for goats to avoid condensed tannins in blackbrush. Am. NaL. 136: 810-828.

Provenza. F.D., J.A. Pfister. and CD. Cheney. 1992. Mechanisms of learning in diet selection with reference to phytotoxicosis In herbivores. J. Range Manage. 45: 36-45.

41

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42

Table 3.2. Mean intake of alfalfa hay ration by lambs before and after intraruminal dosing with ground mesquite leaves.

Mesquite Dose g/kgBW

Before

DayO

intake in g/kg BW

After

Day 1 Day 2 Day 3

20.1(1.0)» 20.1(1.0)' 20.1(1.0)" 20.1(1.0)-

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4.5 17.9(3.1)' 15.2(2.8)' 8.6(1.8)' 12.1 (2.8)'

Means followed by the same superscripts in colums are not different (P > 0.05)

43

CHAPTER IV

SEASONAL TRENDS OF NUTRIENT COMPONENTS OF

MESQUITE LEAVES

Abstract

The objective of this study was to gather information about changes of

nutrients in mesquite leaves across seasons. Knowledge of seasonal changes in

nutrients will be complemented with allelochemical analysis, looking for ways to

increase mesquite utilization by grazing animals in the future. Analysis of mesquite

leaf samples included determinations of dry matter (DM), nitrogen (N). neutral

detergent fiber (NDF). acid detergent fiber (ADF). and in vitro dry matter digestibility

(IVDMD). Samples were collected from 10 mature, medium-size trees each month

from May to November 1995. Dry matter showed an increasing trend with season

from 42 % in May, to 58% in November. Content of N decreased with season (P

< 0.01) with a maximum of 2.73% in May, and a minimum of 1.58 % in November.

Analysis of ADF and NDF indicated similar curvilinear patterns with a significant

effect of months (P <0.01). Minimum content of fiber was found in May. (23.7%

ADF; 32.0% NDF). maximum levels were reached in June before flowering (32.9%

ADF; 43.1% NDF), and decreased again in November (29% ADF; 38.8% NDF).

IVDMD was similar for May and June (79%) and decreased significantly (P<0.01)

for the remaining months, from 74% in July to 69% in November. Positive

correlation with %N may indicate no effects of N allelochemicals on digestibility.

44

Introduction

Nutritive quality of most forages shows great seasonal variation. Generally,

concentration of nutrients in plants depends on the stage of plant growth. Cell

solubles, crude protein, and phosphorus concentrations reach their maximum levels

in actively growing plants, and decline as plants mature and become dormant

(Holechek 1989). Phosphorus, carotene, and protein in browse generally decline

less than grasses as the growing season progresses. Thus, diets based on

mixtures of grasses and browse can usually provide a more balanced nutrition than

grasses or browse alone (Vallentine 1990). However, the presence of toxins and

digestion inhibitors, like lignin and tannin, in woody plants often lowers their

nutritive value (Cates and Rhodes 1977).

Honey mesquite is a shrub that withstands periods of moisture stress

because its roots can penetrate more than 15 m to reach deep soil moisture (Meyer

et al. 1971). Therefore, mesquite has green foliage when herbaceous plants

become dormant. Like other woody species, mesquite growth patterns depend on

fluctuations of temperature and available moisture. Bud break in mesquite starts

between the middle of March and the first week of April, after winter chilling

requirements are met (Dahl 1982). After bud break, twig elongation and rapid leaf

growth last about 6 weeks. Flowers emerge about the time twig elongation ceases

and leaves have reached full size. Twig elongation ceases in midsummer, although

new leaf growth can be stimulated by rainy periods. Most leaves and

inflorescences are produced on current-year stems, which grow in April and May

45

in Texas (Meyer et al. 1971). Mesquite becomes dormant by fall, and leaf abscision

starts generally in November and December, stimulated by frosts and Insects (Dahl

1982).

As mentioned above, nutritional value of grasses and shrubs are often

complementary. Shrubs can be incorporated into management strategies to better

meet animal nutrient demands. Successful management of grasses and palatable

shrubs can show advantages such as better animal gains (Vallentine 1990).

However, the design of efficient grazing management strategies requires basic

information of seasonal changes in nutrients levels. Mesquite leaves collected in

September and October are of apparent good quality as indicated by chemical

analysis of nitrogen (N). neutral detergent fiber (NDF). and acid detergent fiber

(ADF) (Table 2.1). Thus, mesquite could be incorporated into shrub-grass

management systems once its chemical defenses are identified and overcome.

The general objective of this study was to examine seasonal changes in

some important nutrients of mesquite leaves. Seasonal variation of other major

nutrients and allelochemicals will be completed in the future by K.L. Launchbaugh.

The specific objective of this study was to characterize the dynamic of DM, N, NDF,

ADF. and IVDMD of mesquite leaves throughout the growing season. Information

of the basic parameters of nutritive value in leaves, complemented with quantitative

information about defensive compounds, may lead to the development of efficient

grazing management methods for mesquite dominated rangeland.

46


Description of Collection Area

Mesquite leaves were collected at the Texas Tech Experimental Ranch, near

Justiceburg, Texas. The ranch is 106 km southeast of Lubbock. The study area

was a honey mesquite {Prosopis glandulosa var. glandulosa) - tobosagrass {Hilaria

mutica) vegetation type. Sampled areas were uniform in vegetation type, soil type,

and topography.

Sampling Procedure

Medium size, mature mesquite trees (n=10) were chosen randomly the first

week of the months May through November. Mesquite leaves were plucked

randomly from the accessible parts of the tree and sealed in plastic bags. Different

trees were sampled each month to avoid induced modifications of chemical

defenses as a result of the previous collection. After the collection of leaves, each

tree was marked with colored surveyors ribbon to avoid repeated sampling of the

same tree. Bags were then closed and marked with the collection date and tree

number. During transportation to the laboratory, the bags were stored with ice to

keep leaves fresh, and to avoid volatilization of plant compounds. Sealed samples

were stored frozen until they were analyzed.

47

Laboratory Analysis

In preparing mesquite samples for analysis, leaves were put in paper bags,

weighed, and oven-dried at 60X for dry matter (DM) determination. All samples

were ground in a Wiley mill to pass through a 1 mm screen. Half of the sample from

each tree was left frozen in plastic bags for allelochemical analysis. Mesquite

leaves were analyzed for nitrogen (Kjeldahl; AOAC 1984). Neutral Detergent Fiber

(NDF) and Acid Detergent Fiber (ADF) were determined separately for each sample

by the filter bag technique (Komarek et al. 1994), a modification of the conventional

Van Soest fiber analysis (Van Soest et al. 1991). In vitro dry matter digestibility

(IVDMD) was determined by the Barnes modification (Harris 1970) of the Tilley and

Terry (1963) in vitro digestion technique. Rumen fluid, collected from a fistulated

steer fed with alfalfa hay, was mixed into a 1:1 ratio with McDougall's buffer solution

under anaerobic conditions. Tubes with 0.5 g duplicated mesquite samples were

added 15 ml of buffer solution, inoculated with 15 ml of the buffer-solution/rumen

fluid, and incubated for 48 hrs. at 39°C. After 48 hrs., 0.2 pepsin solution and 0.5

ml of concentrated HCL were added to the tubes. Tubes were then incubated for

24 hrs., and centrifugated for 20 min. before drying, for digested DM determination.

Experimental Design

Data from mesquite leaves were analyzed with general linear model

procedures (SAS 1996), with months as treatments and trees as replicates.

Differences between means were determined using Fisher's protected LSD.

48


Dry Matter Seasonal Variatinn

Mesquite leaves showed significant seasonal changes for DM content (P <

0.01; Table 4.1). Minimum average DM 42%, was recorded at the initial growing

season (May 95) and maximum DM content, 58% was recorded at the final stage

of growth (Nov. 95). Dry matter concentration of plants varies with weather

conditions, species, and stage of maturity (Minson 1990). Therefore, increasing

DM in mesquite leaves throughout the growing season can be attributed to

decreasing external moisture, and maturity.

Nitrogen Seasonal Variation

Nitrogen content of mesquite leaves varied significantly across months (P <

0.01; Table 4.1). The maximum value of N was recorded at the first sampling in

May 1995, and the minimum N level was reached in the fall season (November

1995). Mean separation between months revealed significant decrease of N in

June, when compared to May. Nitrogen content remained constant between June

and August and started to decrease again in September. October showed no

significant change in N content when compared to September. Finally. N declined

sharply in November as fall leaf loss began. Therefore, concentration of

nitrogenated compounds in mesquite leaves was negatively correlated with age.

49

ADF and NDF Seasonal Variation

Acid Detergent Fiber (ADF) values, showed a cun/ilinear pattern of seasonal

variation with a significant effect of months on the ADF content (P < 0.01; Table

4.1). Leaves in May had the minimum content of ADF but. the ADF content in June

reached its maximum value. The mean values of ADF remained constant from June

to September, and then decreased slowly as the leaves became older. A possible

explanation for this pattern of fiber content is the rapid expansion of leaves in the

first month, before the flowering season. Further decrease in fiber content

throughout the season could only be explained by a dilution effect of increasing cell

solubles at the final phonological stages of mesquite.

Neutral Detergent Fiber (NDF) in mesquite leaves followed a similar pattern

as ADF. Months affected the content of NDF (P < 0.01; Table 4.1). NDF reached

a maximum value in June, remained nearty constant between June and September,

and then decreased slightly. Mean values of NDF in October and November were

not different (P > 0.05). NDF values were constantly higher than ADF. The

constant difference between NDF and ADF was approximately 9%, and it can be

attributed to the presence of hemicellulose in the NDF fraction (Van Soest 1994).

In Vitro Drv Matter Digestibility

In vitro DM digestibility (IVDMD) was strongly affected by months (P<0.01;

Table 4.1). following a decreasing trend as leaves became older. Samples from

May and June showed similar coefficients of IVDMD (79%) and they were different

50

from the IVDMD of the remaining months (P <0.05). IVDMD values ranged from

74% in July to 70% in November with no statistical differences among them

(P>0.05; Table 4.1). Higher coefficients of digestibility in May and June were in

accordance with higher contents of N in eariy Spring. However, fiber fractions

(NDF and ADF) reached maximum values in June (Table 4.1). Thus, IVDMD

seemed to indicate no detrimental effects of fiber fractions and nitrogenated

allelochemicals on digestibility. Therefore, lower IVDMD of mesquite leaves,

collected from July to November, suggested negative effects of other compounds.

Other compounds probably related to lower digestibility values of mesquite leaves

are phenolic. Although seasonal changes of phenolic are unknown, there is

experimental evidence that in vitro digestibility of leaves was negatively correlated

with phenolic compounds in various species of Prosopis (Lyon 1988).


Nutrient components in mesquite leaves showed strong effect of seasons

between May and November 1995. Dry matter followed an increasing trend

attributed to decreasing external moisture and increasing maturity. Minimum

content of DM contrasted with maximum content of N in May, and both nutrients

were negatively correlated across months.

Similar patterns of curvilinear variation for ADF and NDF contents revealed

a major increase in fiber content from May to June. This rapid change in fiber could

be explained by fast development and maturation of leaves before flowering. After

51

June, ADF and NDF decreased slowly until November, revealing a dilution effect

of increasing amounts of non-fiber components as leaves became older. Cell

content compounds that could account for this dilution effect include sugars, lipids,

pectin, and starch (Van Soest 1994). IVDMD decreased as leaves became older,

showing no detrimental effect of fiber fractions (NDF and ADF). or presumably high

contents of nitrogenated allelochemicals. Lower digestibility of mesquite leaves

from July to November could be explained by a negative effect of other compounds

like phenolics.

Although there are other nutritional factors to be considered before

recommending the best time for mesquite utilization, it is possible to suggest

utilization between September and October. Values of nutrient components in

September and October indicated decreasing levels of fiber ADF and NDF,

increasing levels of cell contents, constant levels of DM, and decreasing content

of N. Decreasing levels of N could be desirable if the chemical defenses of

mesquite are nitrogenated allelochemicals as suggested by Cates and Rhodes

(1977). Therefore, mesquite would probably cause minimum negative effects on

hervibores in November, but September and October offer more potential forage

yield. Grazing management programs based on the use of mesquite leaves In late

fall also would have the advantage of supplying nutrients to animals when high

quality herbaceous forage is generally not available.

52

Literature Cited

AOAC. 1984. Official methods of analysis. (14th Ed). Assoc, of Official Analytical Chem.. Washington, D.C.

Cates, R.G. and D.F. Rhoades. 1977. Prosopis leaves as a resource for insects, p. 61-83. In: B. B. Simpson (ed.) Mesquite: Its biology in two desert ecosystems. Dowden, Hutchinson & Ross, Inc.. Stroudsburg. Penn.

Dahl. B.E. 1982. Mesquite as a rangeland plant, p. A1-A20. In: H.W.Parker (ed.) Mesquite utilization. Symposium on mesquite utilization. Texas Tech Univ. Press. Lubbock. Tex.

Harris, L.E. 1970. Nutrition research techniques for domestic and wild animals. Vol. 1. L.E. Harris, Logan, Ut.

Holechek, J.L., R. Pieper, and C.H. Herbel. 1989. Range management: principles and practices. Prentice-Hall, Inc., Englewood Cliffs, N.J.

Komarek, A.R.. J.B. Robertson, and P.J. Van Soest. 1994. A comparison of methods for determining ADF using the filter bag technique versus conventional filtration. J. Dairy Sc. 77: Suppl. 1.

Lyon, C.K., M.R. Gumbmann, and R. Becker. 1988. Value of mesquite as a forage. J. Sci. Food. Agric. 44:111-117.

Meyer. R.E., H.L. Morton, R.H. Haas, E.D. Robison, and T.E. Riley. 1971. Morphology and anatomy of honey mesquite. Agricultural Research Service. USDA. Tech. Bull. 1423.

Minson. D.J. 1990. Forage in ruminant nutrition. Academic Press. Inc., San Diego. Ca.

SAS. 1996. Statistical analysis system. Ver. 6.02. Cary. N.C.

Tilley, J.M., and R.A. Terry. 1963. A two-stage technique for the in vitro digestion ' of forage crops. J.Brit Grassland Soc. 18:104-111.

Vallentine, J.F. 1990. Grazing management Academic Press, Inc. San Diego, Ca.'

Van Soest, P.J. 1994. Nutritional ecology of the ruminant. Cornell University Press, Ithaca. N.Y.

53

Van Soest, P.J., J.B. Robertson, and B.A. Lewis. 1991. Methods for dietary fiber, neutral detergent fiber and non-starch polysaccharides in relation to animal nutrition. J. Dairy Sci. 74: 3583-3597.

54

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55

CHAPTER V

GENERAL RESEARCH CONCLUSIONS

Mesquite leaves and alfalfa hay had similar nutrient components when

compared by laboratory methods. Increasing levels of mesquite leaves added to

alfalfa hay did not change parameters of nutritional quality of the diet. Basic

parameters determined in laboratory were crude protein (CP), in situ digestibility,

neutral detergent fiber (NDF). acid detergent fiber (ADF). and gross energy (GE).

However. 100% alfalfa was more digestible than 100% pure mesquite, when

studying digestibility by in situ Dacron bag technique.

Mesquite leaves, at levels higher than 5% in the diet, strongly decreased

voluntary intake of lambs, but did not alter relative digestibility parameters.

Apparent DM digestibility, and retained GE were not affected by increasing levels

of mesquite. However, when considering expected higher digestibility for lower

amounts of intake, mesquite may have had a negative effect on digestibility. Low

intake at levels of mesquite > 5% was related to weight loss and negative Nitrogen

balance. High levels of urinary N suggested deamination of body proteins as an

alternative energy source.

Potential toxic effects were suggested by symptoms of diahrrea and strong

conditioned flavor aversion (CFA). Toxic or negative postingestive effect from

Intake of mesquite leaves may have been the main factor of decreasing intake.

Although low levels of specific liver enzymes in blood did not reveal liver necrosis,

56

more detailed analysis of liver activity is necessary to assess mesquite toxic effects.

Decreasing intake and presumably toxic effects caused by mesquite may be

attributed to one or several allelochemicals in mesquite leaves. More research is

needed to identify the specific chemicals and mechanisms of unpalatability.

Tolerance of high mesquite consumption was observed in some individuals.

The high variation between animals needs to be further studied. Animals that

formed weak CFA may have a greater ability to detoxify or tolerate mesquite

allelochemicals. Understanding the mechanisms of detoxification or tolerance may

explain differences in the voluntary intake of mesquite and may lead to ways to

increase the consumption of mesquite by livestock.

Nutrient components in mesquite leaves changed markedly throughout the

growing season. Similar patterns of curvilinear variation for ADF and NDF contents

revealed a major increase in fiber content from May to June. This rapid change in

fiber could be attributed to rapid development of leaves before flowering.

November showed low fiber content, caused probably by a dilution effect of

increasing non-fiber components. Decreasing content of N throughout the growing

season was probably correlated to decreasing contents of some allelochemicals.

However, decreasing values of in vitro digestibility suggested the presence of other

chemical defenses. Seasonal low levels of N could be desirable if the chemical

defenses of mesquite are nitrogenated allelochemicals. September and October

are probably the best months for mesquite utilization, with minimum potential

negative effects on ruminants.

57

APPENDIX

INTAKE OF DRY AND FRESH MESQUITE LEAVES

58

Introduction

Mesquite leaves presumably contain defensive chemicals that affect

palatability and intake. Therefore, before starting expertments on apparent

digestibility of mesquite in a metabolism trial, I conducted an experiment to assess

differences in intake between dry and fresh mesquite leaves. I hypothesized, if

mesquite has volatile defensive compounds, those chemicals would be removed by

drying and thus dried mesquite leaves would be more palatable than fresh leaves.


Mesquite leaves collected from a location near Lubbock. Texas were divided

in 2 groups. The first group of leaves was oven-dried for 48 hours at 55*'C before

offering them to lambs. The second group of leaves was maintained fresh in a

refrigerator. Crossbred lambs (n=18) were assigned to 6 groups and put in

individual pens. The lambs were offered diets with dried or fresh mesquite mixed

with alfalfa hay at levels 10%. 30%, and 50% (DM basis) and offered twice a day.

Results

Data of voluntary intake, analyzed as a factorial design with repeated

measures (Table 1) showed no significant differences between dry and fresh

mesquite leaves (P >0.05). Thus, palatability of mesquite leaves did not change as

a result of the drying process.

59

Table A.1 Average daily DM Intake (g/kg BW) of dry and fresh mesquite leaves eaten by lambs. Treatments were offered at 10, 30, and 50% levels mixed with alfalfa hay. Means are followed by SE in columns.

Treatment

Dry 10% SE

Dry 30% SE

Dry 50% SE

Fresh 10% SE

Fresh 30% SE

Fresh 50% SE

1

13.9 (2.4)

4.6 (1.2)

6.4 (0.8)

10.7 (3.4)

13.2 (3.0)

4.5 (1.2)

2

11.7 (2.0)

5.5 (0.4)

6.1 (0.3)

11.4 (2.0)

11.5 (2.9)

4.8 (1.6)

Days

3

11.2 (1.7)

6.0 (0.9)

3.9 (0.1)

13.3 (2.0)

10.8 (3.9)

4.7 (1.6)

4

13.0 (0.6)

6.4 (1.4)

6.4 (0.7)

12.0 (2.4)

12.4 (2.6)

3.6 (1.5)

5

13.0 (2.7)

7.2 (0.9)

6.4 (0.9)

12.6 (3.1)

12.8 (1.7)

3.0 (1.3)

Average

12.6 (1.7)

5.9 (0.6)

5.8 (0.2)

12.0 (1.7)

12.1 (2.5)

4.1 (1.1)

Subtotals

24.33

28.25

60

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Center, I agree that the Library ancJ my major cJepartment shall make it freely

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nutritional quality of mesquite (prosopis glandulosa) …

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