- Email: [email protected]
The effect of level of feeding on water turnover in growing pigs
Applied Animal Behaviour Science, 12 (1984) 103--109 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
103
THE EFFECT OF LEVEL OF FEEDING ON WATER TURNOVER IN GROWING 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 receiving 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 reducing to 34 g kg-1 at the end of the experiment (about 19 weeks of age, 68.6 kg). During 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 significantly 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 intake 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 decreased below 30 g kg -1 body weight.
INTRODUCTION A n i m a l s usually e x h i b i t a close a n d p o s i t i v e r e l a t i o n s h i p b e t w e e n t h e a m o u n t o f a p a r t i c u l a r f e e d e a t e n a n d t h e a m o u n t o f w a t e r ingested ( L e i t c h a n d T h o m s o n , 1 9 4 4 ; C h e w , 1965). H o w e v e r , g r o w i n g pigs e n h a n c e t h e i r w a t e r i n t a k e significantly w h e n t h e f e e d s u p p l y is a b r u p t l y r e d u c e d . I n c o n trast, w h e n f e e d i n t a k e is s u d d e n l y increased, w a t e r i n t a k e declines slightly o r r e m a i n s u n c h a n g e d . This d r i n k i n g b e h a v i o r s h o w n b y g r o w i n g pigs has b e e n a t t r i b u t e d t o a b d o m i n a l filling ( Y a n g et al., 1981). G r o w i n g pigs h a v e large a p p e t i t e s relative t o b o d y weight. T h e r e f o r e it is n o t surprising t o 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.
104 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 random within equal sex {gilts and barrows) and weight (30 kg) groups to one of the 3 feeding regimes shown in Table I. An air
105 TABLE I Feed allowance for 3 groups of pigs receiving the same diet Study week
0 1 2 3 4 5 6 7 8 9
Ration R,
Ration R~
Ration R 3
Liveweight (kg)
Feed ( g kg-')
Liveweight (kg)
Feed (g kg-')
Liveweight (kg)
Feed (g kg-')
27.8 31.9 36.1 41.0 46.8 51.8 56.3 60.9 64.9 68.6
47 47 47 46 43 43 39 36 34
28.7 32.4 36.0 40.4 45.3 49,8 53.4 56,9 60,1 63,2
43 43 44 42 40 36 34 32 30
30.6 33.6 37.0 41.0 44.8 48.0 51.1 53.9 56.6 59.0
39 39 38 34 31 29 27 26 25
Animals were aged about 10 weeks at Week 0. TABLE II Performance of pigs fed at 3 different levels Ration
Weight gain (g/day) Feed/wt. gain (kg kg-') Body water Initial (ml kg-') Final (ml kg-') Body water gain (ml/day) Feed/bodywater gain (kg I-')
SEM
R,
R,
R3
648 a 2.95
548 b 3.02
451 c 3.03
18 0.04
680 660 419 a
673 655 351 b
677 678 206 c
6 7 13
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 significant e f f e c t o f level o f f e e d i n g o n w a t e r t u r n o v e r e x p r e s s e d as m l 1-', 1, m l k g - ' or m l kg -°'s2. T h e e f f e c t o f age, h o w e v e r , was significant f o r t u r n o v e r r a t e in m l 1- ' , 1 a n d m l kg -~, b u t n o t f o r m l kg -°~2 (Fig. 1). A significant i n t e r a c t i o n e x i s t e d b e t w e e n t r e a t m e n t s a n d age w h e n t u r n o v e r was r e l a t e d t o b o d y w e i g h t ( m l k g - ' or m l kg-°~2), i n d i c a t i n g t h a t t h e r e w e r e d i f f e r e n c e s a m o n g s o m e o f t h e t r e a t m e n t s as t h e s t u d y p r o c e e d e d . T h e c h a n g i n g p a t t e r n o f t u r n o v e r r a t e w i t h age is clearly illustrated in Fig. 1; t u r n o v e r values in m l kg -1 a n d m l kg -°~2 f o r R3 g r a d u a l l y increased t h r o u g h o u t the feeding p e r i o d , while t h o s e f o r R , a n d R2 increased slightly t o t h e f o u r t h w e e k a n d
106
m
RationNS TimeP
2ooI
150" 8.0 .~" Z0 6.0
RationNS TimeP
I
~
5.0 ~ 4.0
I--~
170 f
~
~
RationNS R×TP
E 130f 110" C~ iiif
~
~
N$ RationNS
J
Time
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 analysis 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 effect 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
107 TABLE III
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
2 4 7 9
m l kg -°.s2
m l k g -1
R! --R 2
R 2-R 3
R I-R
--7 a --5 a --3 a --I a
14 a 23 a - - 7 ab --26 b
7a 18 a - - 9 ab --26 b
3
RI-R --14 a --9 a --3 a --2 a
2
R 2-R~
R1-R 3
24 a 44 a - - 1 2 ab --51 b
10 a 35 a - - 1 4 ab --19 b
Differences in the same column bearing different superscript letters are significant a t P < 0.05.
developed. The higher water consumption was n o t evident, however, when the turnover volume (1) was considered (Fig. 1). Comparison of actual volume 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), clearly 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 intake may represent oral and gastric needs, and probably acts as a fail-safe mechanism to preserve homeostasis (Nicolaidis and Rowland, 1975). Growing pigs tend to drink about 3 times as much water as the weight of dry matter eaten under normal feeding and environmental (20 ° C) conditions (Leitch and Thomson, 1944). Restricting the water:feed ratio to half normal, however, 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 subtracting 0.55 from the ratios of water turnover (1) to feed intake, since every kg of air
108
week of the study. It is estimated (assuming a daily turnover rate of 114 ml kg-~, or t h a t 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 consumed at t h a t 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 a m o u n t of water required to meet the pigs' physiological needs. R2 pigs also received less feed than R1 pigs, but they did not show any indication 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. Polydipsia 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 polydipsia 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.
REFERENCES Barber, R.S., Braude, R. and Mitchell, K.G., 1963. Further studies on the water requirements of the growing pigs. Anita. Prod., 5: 277--282. Castle, E.J. and Castle, M.E., 1957. Further studies of the rate of passage of feed through the alimentary tract of pigs. J. Agric. Sci., 49: 106--112. 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: 30-32. Kutscher, C.L., 1973. Food-deprivation polydipsia in gerbils. Lack of adaptive value and termination with carbohydrate feeding. Physiol. Psyehol., 1: 125--128. Leitch, M.A. and Thomson, J.S., 1944. The water economy of farm animals. Nutr. Abstr. Rev., 13" 197--223. Macfarlane, W.V., 1965. Water metabolism of desert ruminants. In" D.R. Curtis and A.K.M. McIntyre (Editors), Studies in Physiology. Springer-Verlag, Berlin, pp. 191-199. Nicol, S.C., 1978. Rates of water turnover in marsupials and eutherians: A comparative review w i t h n e w data o n the Tasmanian devil. A u s t . J. Zool., 26: 465--473.
109
Nicolaldis, S. and Rowland, N., 1975. Systemic versus oral and gestro-intestinal metering of fluid intake. In: G. Peters, J.T. Fitzsimons and L. Peters-I-Iaefeli (Editors), Control Mechanisms of Drinking. Sprinpr-Verlq, New York, pp. 14--21. Peters, G., 1980. Mecani-m de reglage de l'ingestion d'eau. J. Physiol., Paris, 76: 295-322. Steel, G.D. and Torrie, J.H., 1980. Principles and Procedures of Statistics; a Biometrical Approach. 2nd Edn., McGraw-Hill, New York. Yang, T.S., Howard, B. and Macfarlane, W.V., 1981. Effects of food on drinking behaviour of growing pigs. Appl. Anita. Ethol., 7: 259--270.
103
THE EFFECT OF LEVEL OF FEEDING ON WATER TURNOVER IN GROWING 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 receiving 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 reducing to 34 g kg-1 at the end of the experiment (about 19 weeks of age, 68.6 kg). During 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 significantly 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 intake 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 decreased below 30 g kg -1 body weight.
INTRODUCTION A n i m a l s usually e x h i b i t a close a n d p o s i t i v e r e l a t i o n s h i p b e t w e e n t h e a m o u n t o f a p a r t i c u l a r f e e d e a t e n a n d t h e a m o u n t o f w a t e r ingested ( L e i t c h a n d T h o m s o n , 1 9 4 4 ; C h e w , 1965). H o w e v e r , g r o w i n g pigs e n h a n c e t h e i r w a t e r i n t a k e significantly w h e n t h e f e e d s u p p l y is a b r u p t l y r e d u c e d . I n c o n trast, w h e n f e e d i n t a k e is s u d d e n l y increased, w a t e r i n t a k e declines slightly o r r e m a i n s u n c h a n g e d . This d r i n k i n g b e h a v i o r s h o w n b y g r o w i n g pigs has b e e n a t t r i b u t e d t o a b d o m i n a l filling ( Y a n g et al., 1981). G r o w i n g pigs h a v e large a p p e t i t e s relative t o b o d y weight. T h e r e f o r e it is n o t surprising t o 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.
104 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 random within equal sex {gilts and barrows) and weight (30 kg) groups to one of the 3 feeding regimes shown in Table I. An air
105 TABLE I Feed allowance for 3 groups of pigs receiving the same diet Study week
0 1 2 3 4 5 6 7 8 9
Ration R,
Ration R~
Ration R 3
Liveweight (kg)
Feed ( g kg-')
Liveweight (kg)
Feed (g kg-')
Liveweight (kg)
Feed (g kg-')
27.8 31.9 36.1 41.0 46.8 51.8 56.3 60.9 64.9 68.6
47 47 47 46 43 43 39 36 34
28.7 32.4 36.0 40.4 45.3 49,8 53.4 56,9 60,1 63,2
43 43 44 42 40 36 34 32 30
30.6 33.6 37.0 41.0 44.8 48.0 51.1 53.9 56.6 59.0
39 39 38 34 31 29 27 26 25
Animals were aged about 10 weeks at Week 0. TABLE II Performance of pigs fed at 3 different levels Ration
Weight gain (g/day) Feed/wt. gain (kg kg-') Body water Initial (ml kg-') Final (ml kg-') Body water gain (ml/day) Feed/bodywater gain (kg I-')
SEM
R,
R,
R3
648 a 2.95
548 b 3.02
451 c 3.03
18 0.04
680 660 419 a
673 655 351 b
677 678 206 c
6 7 13
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 significant e f f e c t o f level o f f e e d i n g o n w a t e r t u r n o v e r e x p r e s s e d as m l 1-', 1, m l k g - ' or m l kg -°'s2. T h e e f f e c t o f age, h o w e v e r , was significant f o r t u r n o v e r r a t e in m l 1- ' , 1 a n d m l kg -~, b u t n o t f o r m l kg -°~2 (Fig. 1). A significant i n t e r a c t i o n e x i s t e d b e t w e e n t r e a t m e n t s a n d age w h e n t u r n o v e r was r e l a t e d t o b o d y w e i g h t ( m l k g - ' or m l kg-°~2), i n d i c a t i n g t h a t t h e r e w e r e d i f f e r e n c e s a m o n g s o m e o f t h e t r e a t m e n t s as t h e s t u d y p r o c e e d e d . T h e c h a n g i n g p a t t e r n o f t u r n o v e r r a t e w i t h age is clearly illustrated in Fig. 1; t u r n o v e r values in m l kg -1 a n d m l kg -°~2 f o r R3 g r a d u a l l y increased t h r o u g h o u t the feeding p e r i o d , while t h o s e f o r R , a n d R2 increased slightly t o t h e f o u r t h w e e k a n d
106
m
RationNS TimeP
2ooI
150" 8.0 .~" Z0 6.0
RationNS TimeP
I
~
5.0 ~ 4.0
I--~
170 f
~
~
RationNS R×TP
E 130f 110" C~ iiif
~
~
N$ RationNS
J
Time
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 analysis 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 effect 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
107 TABLE III
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
2 4 7 9
m l kg -°.s2
m l k g -1
R! --R 2
R 2-R 3
R I-R
--7 a --5 a --3 a --I a
14 a 23 a - - 7 ab --26 b
7a 18 a - - 9 ab --26 b
3
RI-R --14 a --9 a --3 a --2 a
2
R 2-R~
R1-R 3
24 a 44 a - - 1 2 ab --51 b
10 a 35 a - - 1 4 ab --19 b
Differences in the same column bearing different superscript letters are significant a t P < 0.05.
developed. The higher water consumption was n o t evident, however, when the turnover volume (1) was considered (Fig. 1). Comparison of actual volume 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), clearly 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 intake may represent oral and gastric needs, and probably acts as a fail-safe mechanism to preserve homeostasis (Nicolaidis and Rowland, 1975). Growing pigs tend to drink about 3 times as much water as the weight of dry matter eaten under normal feeding and environmental (20 ° C) conditions (Leitch and Thomson, 1944). Restricting the water:feed ratio to half normal, however, 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 subtracting 0.55 from the ratios of water turnover (1) to feed intake, since every kg of air
108
week of the study. It is estimated (assuming a daily turnover rate of 114 ml kg-~, or t h a t 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 consumed at t h a t 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 a m o u n t of water required to meet the pigs' physiological needs. R2 pigs also received less feed than R1 pigs, but they did not show any indication 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. Polydipsia 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 polydipsia 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.
REFERENCES Barber, R.S., Braude, R. and Mitchell, K.G., 1963. Further studies on the water requirements of the growing pigs. Anita. Prod., 5: 277--282. Castle, E.J. and Castle, M.E., 1957. Further studies of the rate of passage of feed through the alimentary tract of pigs. J. Agric. Sci., 49: 106--112. 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: 30-32. Kutscher, C.L., 1973. Food-deprivation polydipsia in gerbils. Lack of adaptive value and termination with carbohydrate feeding. Physiol. Psyehol., 1: 125--128. Leitch, M.A. and Thomson, J.S., 1944. The water economy of farm animals. Nutr. Abstr. Rev., 13" 197--223. Macfarlane, W.V., 1965. Water metabolism of desert ruminants. In" D.R. Curtis and A.K.M. McIntyre (Editors), Studies in Physiology. Springer-Verlag, Berlin, pp. 191-199. Nicol, S.C., 1978. Rates of water turnover in marsupials and eutherians: A comparative review w i t h n e w data o n the Tasmanian devil. A u s t . J. Zool., 26: 465--473.
109
Nicolaldis, S. and Rowland, N., 1975. Systemic versus oral and gestro-intestinal metering of fluid intake. In: G. Peters, J.T. Fitzsimons and L. Peters-I-Iaefeli (Editors), Control Mechanisms of Drinking. Sprinpr-Verlq, New York, pp. 14--21. Peters, G., 1980. Mecani-m de reglage de l'ingestion d'eau. J. Physiol., Paris, 76: 295-322. Steel, G.D. and Torrie, J.H., 1980. Principles and Procedures of Statistics; a Biometrical Approach. 2nd Edn., McGraw-Hill, New York. Yang, T.S., Howard, B. and Macfarlane, W.V., 1981. Effects of food on drinking behaviour of growing pigs. Appl. Anita. Ethol., 7: 259--270.