Applied Animal Behaviour Science, 12 (1984) 103--109 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands 103

T H E E F F E C T O F L E V E L O F F E E D I N G O N W A T E R T U R N O V E R I N G R O W I N G PIGS

T.S. YANG ~, M.A. PRICE and F.X. AHERNE

Department of Animal Science, University of Alberta, Edmonton, Alberta, T6G 21"11 (Canada)

(Accepted for publication 23 August 1983)

ABSTRACT

Yang, T.S., Price, M.A. and Aharne, F.X., 1984. The effect of level of feeding on water turnover in growing pigs. Appl. Anim. Behav. Sci., 12: 103--109.

Water turnover was measured by tritium dilution in 3 groups of 8 growing pigs receiv- ing different amounts of the same diet for 9 weeks. Control pigs (Ration R~) were fed 47 g/kg body weight initially (about 10 weeks of age, 27.8 kg liveweight), gradually re- ducing to 34 g kg -1 at the end of the experiment (about 19 weeks of age, 68.6 kg). Dur- ing the same time-period, a second group of pigs were fed Ration R2, consisting of 42 g kg -I initially (28.7 kg liveweight), reducing to 30 g kg -1 (68.2 kg); the third group received R3, consisting of 39 g kg -~ (30.6 kg) reducing to 25 g kg -1 (59.0 kg).

There was no significant difference in overall efficiency of feed conversion among pigs fed the three levels of feed. However, daily weight gain for the R~ and R~ pigs was signi- ficantly lower than that of the control pigs (R1). Water turnover rates (ml kg -z and ml kg -°-~2) for R 1 and R 2 pigs were similar in value and also in pattern, tending to decrease throughout the study. R s pigs showed a continuous increase in turnover rate, suggesting the gradual development of an over-drinking (polydipsia) behaviour. The extra water in- take was apparently not for homeostatic purposes, but was probably motivated by hunger. It was evident that pigs showed polydipsia when the daily DM feed intake de- creased below 30 g kg -1 body weight.

INTRODUCTION

Animals usual ly exh ib i t a close and pos i t ive re la t ionsh ip b e t w e e n the a m o u n t o f a pa r t i cu la r feed ea ten and the a m o u n t o f wa t e r ingested (Le i tch and T h o m s o n , 1944; Chew, 1965) . However , g rowing pigs enhance the i r w a t e r i n t ake s ignif icant ly w h e n the feed supp ly is a b r u p t l y reduced . In con- t ras t , w h e n feed in t ake is sudden ly increased, wa t e r in t ake decl ines sl ightly o r r emains unchanged . This dr ink ing behav io r s h o w n b y growing pigs has been a t t r i b u t e d to a b d o m i n a l filling (Yang et al., 1981) . G r o w i n g pigs have large appe t i t e s re lat ive to b o d y weight . T h e r e f o r e i t is n o t surpr is ing to ob-

' Present address: Physiology Division, Pig Research Institute, P.O. Box 23, Chunan, Taiwan, R.O.C.

0168-1591/84/$03.00 © 1984 Elsevier Science Publishers B.V.

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serve that hungry pigs over-drink water to meet volume satisfaction. The feed-deprivation polydipsia is not observed in all animals, and is probably of psychological rather than physiological origin (Kutscher, 1973).

If growing pigs were gradually, rather than suddenly, underfed, it is not known whether the hunger-induced polydipsia would develop. This question was investigated in the present study.

MATERIALS AND METHODS

A total of 24 crossbred (Yorkshire X Lacombe) pigs were assigned at ran- dom within equal sex {gilts and barrows) and weight (30 kg) groups to one of the 3 feeding regimes shown in Table I. An air<lry diet (12% moisture} based on barley, wheat and soybean, containing 175 g protein per kg of dry matter and balanced for vitamins and minerals, was used throughout the study. Animals were housed in groups of 4, in an ambient temperature of 20°C, and were fed individually twice a day at 08.00 and 15.30 h. Water was freely available to each group.

Total body water (TBW) and water turnover were estimated periodically by the dilution of tritiated water. The isotope was diluted in 0.9% saline and injected intramuscularly (300 kBq/kg body weight). The tritium concentra- tion (C1), in water of plasma taken at 7-day intervals, following a 2 h equili- bration (Co), was used to estimate the mean fractional turnover rate (ml 1-1 = 1000.log (Co/C1)tl) of body water for that week (tl = 7 days). The daily turnover was also expressed as actual turnover volume (1) and liveweight- related volume (ml kg -1). Water turnover in mammals appears to be a func- tion of body weight °'82 (Macfarlane, 1965; Nicol, 1978). Comparisons of size-corrected turnover (ml kg-°'82), using this relationships, were also made.

Analysis of variance was used to determine the significance of the main effects (feeding and age) on water turnover, and their interaction. Results with significant interactions were further tested according to the method of Hatter (1970). The Student-Newman--Keuls test was used to compare means (Steel and Torrie, 1980).

RESULTS AND DISCUSSION

The actual changes in body weight of the pigs in the 3 treatment groups are shown in Table I. The differences in feeding levels resulted in significant differences in daily weight gain but not in conversion efficiency of feed to body weight or to TBW {Table II). There was no significant treatment effect on TBW expressed in ml kg -1 among pigs either at the beginning or the end of the study {Table II). However, there was a significant (P < 0.05) treat- ment effect on rate of TBW accumulation (ml/day). The control group (R,) accumulated body water more rapidly than the R2 group, which in turn were more rapid than the R3 group.

The analysis of the water turnover data is summarized in Fig. 1. There was

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TABLE I

Feed allowance for 3 groups of pigs receiving the same diet

Study Ration R, Ration R~ Ration R 3 week

Liveweight Feed Liveweight Feed Liveweight Feed (kg) ( g kg-') (kg) (g kg-') (kg) (g kg-')

0 27.8 28.7 30.6 47 43 39 1 31.9 32.4 33.6 47 43 39 2 36.1 36.0 37.0 3 41.0 47 40.4 44 41.0 38 4 46.8 46 45.3 42 44.8 34 5 51.8 43 49,8 40 48.0 31 6 56.3 43 53.4 36 51.1 29 7 60.9 39 56,9 34 53.9 27 8 64.9 36 60,1 32 56.6 26 9 68.6 34 63,2 30 59.0 25

Animals were aged about 10 weeks at Week 0.

TABLE II

Performance of pigs fed at 3 different levels

Ration SEM

R, R, R 3

Weight gain (g/day) 648 a 548 b 451 c 18 Feed/wt. gain (kg kg-') 2.95 3.02 3.03 0.04 Body water

Initial (ml kg-') 680 673 677 6 Final (ml kg-') 660 655 678 7

Body water gain (ml/day) 419 a 351 b 206 c 13 Feed/bodywater gain

(kg I-') 4.56 4.72 4,46 0.06

Means in the same row bearing different superscript, letters are different at P < 0.001.

n o s ignif icant e f f ec t o f level o f feeding on wa te r t u rnove r expressed as ml 1-', 1, m l kg - ' or ml kg -°'s2. T h e e f f ec t o f age, however , was s ignif icant fo r turn- over ra te in ml 1 - ' , 1 and ml kg -~, b u t n o t fo r ml kg -°~2 (Fig. 1). A signif icant i n t e r ac t i on exis ted b e t w e e n t r e a t m e n t s and age w h e n t u rnove r was re la ted to b o d y we igh t (ml kg- ' or ml kg-°~2), indica t ing t ha t t he re were d i f fe rences a m o n g s o m e o f the t r e a t m e n t s as t he s t u d y p roceeded . The changing p a t t e r n o f t u r n o v e r ra te wi th age is c lear ly i l lus t ra ted in Fig. 1; t u r n o v e r values in ml kg -1 and ml kg -°~2 fo r R3 gradual ly increased t h r o u g h o u t the feeding per iod , while those fo r R , and R2 increased sl ightly to the f o u r t h week and

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Ration NS m Time P<O.OO1 2oo I R×T .s

150"

I 8.0 Ration NS

.~" Z0 Time P<O.OO1 R×T NS 6.0 5.0 ~

~ 4.0

I--- 170 ~ f ~ ~ RationNS

R × T P<O.01

E 130f 110"

C~ ii i f ~ ~ J Ration NS Time N$

240" R1R2R 3 R1R2R 3 R1R2R 3 ~1R2R3 2 4 7 9

Time (Weeks)

Fig. I. Daily water turnover rate (mean +- SEM) of growing pigs fed different levels (R,, R= and R3, see text) of the same diet. Animals were aged about 12 weeks at Week 2 of the study.

then decreased for the remainder of the study. The additional statistical ana- lysis multiple comparison for interaction (Table III) also revealed that changes in turnover rate (ml kg -1 or ml kg -°~2) in R2 were parallel to those in RI while changes in R3 gradually differed from those of R1 and R2 and reached significance in the ninth week of the study. It is clear that when compared to the control (RI), low levels of feeding applied a significant ef- fect to turnover rate in the case of R3 but not 1~ 2.

Water turnover rate normally maintains a constant positive relationship with metabolic rate (Macfarlane, 1965). The decreasing turnover rates shown by animals in R1 and R2, therefore, are presumed to be due to the decreasing metabolic rate which is associated with increasing age. The different pattern of turnover (ml kg -x and ml kg -°~2) found in the R3 pigs suggests that-a higher voluntary intake of water per unit of body weight was gradually

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T A B L E I I I

Mutliple comparison for the interaction between feed intake and age on differences o f water turnover rate in g r o w i n g pigs

Week m l kg -1 ml kg -°.s2

R ! - - R 2 R 2 - R 3 R I - R 3 R I - R 2 R 2 - R ~ R 1 - R 3

2 - -7 a 14 a 7 a - -14 a 24 a 10 a 4 - -5 a 23 a 18 a - -9 a 44 a 35 a 7 - -3 a - -7 ab - -9 ab - -3 a - -12 ab - -14 ab 9 - - I a - -26 b - -26 b - -2 a - -51 b - - 1 9 b

Differences in the same column bearing different superscript letters are significant at P < 0 .05 .

developed. The higher water consumption was not evident, however, when the turnover volume (1) was considered (Fig. 1). Comparison of actual vol- ume in this study is partially artificial; differences in osmotic load (feeding scale) and body size have to be taken into consideration. In Week 9 of the study, R3 pigs, with lower body weight and less solid intake (Table I), showed a similar water turnover volume to the R1 and R2 pigs (Fig. 1), clear- ly demonstrating a greater consumption of water.

Animals usually drink more water than their actual requirement for hydro-mineral balance (Fitzsimons, 1972; Peters, 1980). This extra water in- take may represent oral and gastric needs, and probably acts as a fail-safe mechanism to preserve homeostasis (Nicolaidis and Rowland, 1975). Grow- ing pigs tend to drink about 3 times as much water as the weight of dry mat- ter eaten under normal feeding and environmental (20 ° C) conditions (Leitch and Thomson, 1944). Restricting the water:feed ratio to half normal, how- ever, has little effect on overall performance (Castle and Castle, 1957; Barber et al., 1963), suggesting that the normal intake is excessive in terms of physiological requirements.

The ratio of water to feed intake in this study can be obtained by sub- tracting 0.55 from the ratios of water turnover (1) to feed intake, since every kg of air<lry feed eaten will contribute 0.5--0.6 1 (0.12 1 moisture plus meta- bolic water calculated from the organic component of the feed) to water turnover. The estimated water:feed intake ratios were similar among pigs of the 3 treatments in the second week of the study (averaging 2.68). As the study proceeded, the ratio for R3 pigs increased gradually, while those for RI and R: pigs remained relatively unchanged. At the ninth week, the water:food intake ratio for the R3 pigs (5.198) was significantly higher than that for the R1 (2.86, P <~ 0.01) and R2 (3.34, P <~ 0.05) pigs. The higher water:feed intake ratio shown by the R3 pigs could also be seen as an indica- tion of excess water consumption.

The volume of water turnover in the R3 pigs was 8.03 1/day in the ninth

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week of the study. It is estimated (assuming a daily turnover rate of 114 ml kg -~, or that a water:food intake ratio of 4.1:1 is sufficient for pigs weighing 56.6 kg and fed 1.4 kg/day) that at least 1.5 1/day of excess water was con- sumed at that time. The estimation would be much higher at a lower water:food intake ratio. The actual over-consumption of water is difficult to determine in the absence of data to indicate the minimum amount of water required to meet the pigs' physiological needs.

R2 pigs also received less feed than R1 pigs, but they did not show any in- dication of over-consumption of water. The R2 feed allowance was always maintained at the level of 30 g kg -~ or above (Table I), suggesting that any threshold feeding level for excessive water intake was below this level. Poly- dipsia was gradually exhibited by the R3 pigs after 7 weeks of the study -- a period in which the feed allowance was below 30 g kg -~ (Table II). This provides further support to the suggested threshold level for overdrinking.

There was no evidence that R3 pigs needed extra water for homeostasis in the latter stage of the study. The over-drinking is therefore presumed to be a behavioural trait. It is concluded that gradually reducing feed to below 30 g DM/kg body weight in these pigs resulted in a hunger-induced poly- dipsia similar to that observed in short-term fasted pigs.

ACKNOWLEDGEMENTS

Financial support provided by the Alberta Agricultural Research Trust and the Alberta Pork Producers Marketing Board is gratefully acknowledged. Appreciation is especially expressed to Mr. R. Weingardt for his statistical advice.

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Chew, R.M., 1965. Water metabolism of mammals. In: W.V. Mayer and R.G. Van Gelder (Editors}, Physiological Mammalogy, Vol. 2. Academic Press, New York, pp. 43--178.

Fitzsimons, J.T., 1972. Thirst. Physiol. Rev., 52: 468--561. Harter, H.L., 1970. Multiple comparison procedure for interactions. Am. Stat., 24: 30--

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