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Effect of Feed or Water Restriction on Basal and TRH-Stimulated Growth Hormone Secretion in the Growing Turkey Poult
PHYSIOLOGY AND REPRODUCTION Effect of Feed or Water Restriction on Basal and TRH-Stimulated Growth Hormone Secretion in the Growing Turkey Poult J. A. PROUDMAN and H. OPEL US Department of Agriculture, SEA, AR, Animal Science Institute, Avian Physiology Laboratory, Beltsville, Maryland 20705 (Received for publication December 31, 1979)
1981 Poultry Science 6 0 : 6 5 9 - 6 6 7 INTRODUCTION
Restricted feeding of turkeys and chickens during both the growing and laying periods has been studied extensively (Lee et al., 1971; Balnave, 1973; Krueger et al., 1977), but restricted water intake has received less attention (Kellerup et al., 1965; Spiller et al., 1973). Various restriction regimens have been proposed in an effort to reduce feed costs, control body weight, reduce mortality (particularly of turkeys), and improve reproductive performance. However, the effects of such restrictions on the physiology and metabolism of the growing bird are not well understood. Many regulatory factors operate simultaneously to control growth and metabolic processes. Growth hormone (GH), studied extensively in mammalian species but not in birds, has an important influence on growth and metabolism. Circulating GH levels in the growing turkey are positively correlated with growth rate (Harvey et al., 1977a; Proudman and Wentworth, 1980). Chicken GH stimulates in vitro lipolysis of avian adipose tissue and inhibits insulin-induced lipogenesis by the liver (Harvey et al., 1977b). Although Harvey et al. (1978a) have shown that plasma
GH levels are significantly elevated in the growing chicken during fasting, there have been no studies of the effects of prolonged feed or water restriction on GH secretion in the bird. The present study details these effects in the growing turkey poult. MATERIALS AND METHODS
Thirty Nicholas Large White male turkey poults, 4 weeks of age, were randomly divided into three groups' and placed in individual wire cages equipped with individual feeders and water bottles. A commercial growing diet (20% protein; 3000 kcal/kg ME) was fed throughout the experiment; tap water was warmed to room temperature before use. A 12 hr photoperiod was maintained (lights on at 0600 hr). A week pretreatment period, during which all birds received feed and water ad lib, allowed the birds to adjust to the cage environment. The experimental period commenced when the poults were 6 weeks old. The control group was fed ad lib, die first treatment group was restricted to 50% of the quantity of feed eaten by the controls on the previous day, and the second treatment group was restricted to 50% of die amount of water consumed by the
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ABSTRACT Both feed and water restriction of growing turkeys resulted in an increase in the basal levels of plasma growth hormone (GH). Restricted birds also showed an increased response to thyrotropin-releasing hormone (TRH) stimulation. These changes were significantly greater in feed-restricted birds than in the water-restricted birds. After return to ad lib conditions, basal plasma GH levels remained elevated above control levels in both previously restricted groups. However, the GH response to TRH stimulation returned to normal during this period. The increase in GH secretion during undernutrition is a metabolic adjustment consistent with the known role of GH in glucose, protein and fat metabolism. The elevated GH levels present after return to adequate nutrition may aid compensatory growth. Feed and water restriction were equally effective in limiting the growth of young turkey poults. Body weight gain and feed efficiency were severely affected during the first 3 weeks of restriction, but improved during the 4th week. Return to ad lib conditions resulted in compensatory growth and markedly improved feed efficiency in both restricted groups. Feed-restricted birds showed a significant increase in water consumption after 8 days of restriction. This polydipsia may result from intermittent feeding of hungry animals. Water consumption returned to normal after 1 week of ad lib feeding. Birds restricted in water consumption voluntarily limited their feed intake to a level only slightly higher than that of the feed-restricted group. When water was supplied ad lib, these birds immediately resumed normal feed consumption. (Key words: growth hormone, turkey, feed restriction, water restriction)
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RESULTS
The mean body weights of the control and restricted birds are shown in Figure 1. Birds fed and watered ab lib maintained a nearly-linear rate of growth throughout the experiment and gained an average of 5 3 9 g per week. Restricted birds were significantly lighter than controls after 6 days of restriction and remained lighter throughout the experiment. There was no significant difference between the mean body weight of the birds restricted in feed con-
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8 9 Age (weeks)
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FIG. 1. Mean body weight of Large White male turkeys fed ad lib (•) or restricted in feed consumption (o) or water consumption (A) to 50% of ad lib intake for 4 weeks (n = 10/group). Restricted groups were then returned to ad lib conditions (arrow) for 1 week (n = 5/group). The bars represent ± SEM.
sumption vs. those restricted in water consumption at any of the ages studied. The restricted birds exhibited a very slow rate of gain during the first 3 weeks on the restricted regimens (177 g gain/bird/week) but grew at more than double this rate during the final week of restriction (390 g gain/bird/week). After return to ad lib feed and water, the restricted birds gained at a faster rate than the controls (940 g vs. 640 g gain/bird). The mean daily feed and water consumption for each group are presented in Figures 2 and 3, respectively. The feed consumption of both of the restricted groups was significantly less than that of the control group during the restriction period. Birds restricted in water consumption, but with access to feed ad lib, consumed only slightly more feed than the birds in the 50% feed restriction group. Return to ad lib feeding resulted in a dramatic one-day increase in feed consumption in the restricted feed group, followed by an immediate return to the feed
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controls on the previous day. The restricted feed group received water ad lib, and the water-restricted group was fed ad lib. Restrictions were imposed on the second day of the experiment and continued until the birds were 10 weeks and 1 day of age. At this time, 5 birds from each group were sacrificed for pituitary collection and the remaining 5 were given feed and water ad lib for 1 week. Daily feed and water consumption were measured for each bird; body weights were recorded weekly from 6 to 10 weeks of age, and at the end of the experiment. Blood samples were collected for GH assay by venipuncture into heparinized tubes at weekly intervals and at the end of the experiment. These samples were collected at the same time of day (1000 to 1100 hr), just before weighing and feeding. At 6 and 9 weeks of age, an additional blood sample was collected 2 hr after feeding. At 10 weeks and 1 day of age, all birds were challenged (before feeding) with a 2 /xg/kg dose of thyrotropin releasing hormone (TRH), injected ip in .9% NaCl. Blood samples were collected at 0, 30, 60, and 150 min after TRH administration. At the end of the experiment, the remaining birds were again challenged with TRH as above. All blood samples were refrigerated and centrifuged, and the plasma was stored at —20 C for GH assay. Plasma GH concentration was measured by a homologous radioimmunoassay (Proudman and Wentworth, 1978). The results were examined for statistical differences (P<.05) within time periods by analysis of variance and Duncan's new multiple range test. Significant increases or decreases in hormone levels between adjacent sampling periods, but within treatment groups, were indicated by a significant (P«.05) slope as determined by linear regression analysis. All statistical analyses were performed using the procedures of Barr et al. (1976).
TURKEY GH AND FEED OR WATER RESTRICTION
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Age (weeks)
FIG. 2. Mean daily feed consumption of restricted and unrestricted birds. Refer to legend of Figure 1.
consumption pattern of the control birds. The water-restricted birds increased feed consumption to control levels on the first day of ad lib feeding. Water consumption patterns revealed dramatic differences among all groups. The feedrestricted birds maintained a pattern of water consumption similar to that of the controls for 8 days following the imposition of the restrictions; thereafter, and until the end of the restriction period, they consumed significantly more water than the controls consumed. Return to ad lib feeding resulted in a gradual decline in water consumption by this group to control levels. The water-restricted birds showed a dramatic increase in water intake for several days after return to ad lib conditions, but within 1 week the water consumption levels of these birds also matched those of the control birds. The feed efficiency of each of the groups is shown in Table 1. The restricted birds generally showed significantly poorer feed efficiency
than the controls during the first 3 weeks of restriction. During the 4th week, however, the feed efficiency of the restricted birds improved to equal that of the control group. During the final period (which included 1 day of restriction and 7 days ad lib), the feed efficiency of the previously restricted birds was significantly better than that of the controls; water-restricted birds showed a mean feed efficiency superior to that of the feed-restricted birds. Over the total experiment, feed efficiency did not differ significantly among the three groups. Restriction of feed or water intake resulted in a significant elevation of plasma GH levels within 1 week of imposing the restrictions (Fig. 4). Feed-restricted birds maintained plasma GH levels significantly higher than those of either of the other groups throughout the restricted period; GH levels in the waterrestricted birds exceeded control levels at 7 and 10 weeks of age. Return to ad lib conditions resulted in a significant increase in circulating GH levels in the previously water-restricted
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FIG. 3. Mean daily water consumption of restricted and unrestricted birds. Refer to legend of Figure 1.
birds. Both restricted groups maintained higher GH levels than the controls even after feed and water consumption patterns had returned to normal. The decline in GH levels observed within groups during the experimental period is an expected change associated with increasing age and declining growth rate (Proudman and Wentworth, 1980). Measurement of pre-and postprandial GH levels (not shown) found no change in any
group 2 hr after feeding, either before or after imposition of the restricted regimens. The response to TRH administration, within 30 min of ip injection, was significant in all groups at both time periods studied. Release of GH in response to TRH stimulation was significantly greater in the restricted feed group than in the other groups at the end of the four-week period of restriction (Fig. 5, upper panel). Water-restricted birds showed a greater response
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"£ 500
TURKEY GH AND FEED OR WATER RESTRICTION TABLE 1. Weekly and total feed efficiency1
of restricted and unrestricted
663 turkeys
Feed efficiency2 Age (weeks)
Control
Restricted period: 6-7 7-8 8-9 9-10 Ad lib period: 10-11 Overall: 6-11
Restricted feed
Restricted water
± .067 a ± .056 a ± .026 a ± .102 a
.498 ± .017a .376 + .044b .340 ± .023b .620 ± .062a
.140 ± .060b .549 ± .108ab .383 ± .029b .739 ± .043a
.409 ± .027a
.671 ± .019b
.915 ± .055c
.536 ±.030a
.537 ± .017a
.542 ± .034a
.568 .684 .534 .709
Feed efficiency = gain (g)/feed consumed (g).
2
Mean + SEM; n = 10 during restricted period; n = 5 during ad lib period and overall.
than controls showed, but the differences between these groups were not statistically significant. One week after return to ad lib conditions, the response to TRH stimulation was the same for all groups (Fig. 5, lower panel). DISCUSSION
Restriction of the feed or water intake of
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Age (week)
FIG. 4. Mean plasma GH concentration of restricted and unrestricted birds. Refer to legend of Figure 1.
growing turkey poults had profound effects on growth, feed efficiency, and intake of the unrestricted nutrient, as well as a significant influence on GH secretion. Feed restriction and water restriction were equally effective in limiting the growth of young turkey poults. Body weight gain and feed efficiency were most severely affected during the first 3 weeks of restriction. Gain and efficiency (particularly of the water-restricted birds) substantially improved during the 4 weeks of restriction; such improvement may indicate some metabolic adaptation to the restricted regimen. However, verification of this improvement with a longer restriction period is necessary before any special significance can be attached to this observation. After 4 weeks of restriction, the return to ad lib conditions resulted in rapid growth characterized by very efficient utilization of feed. This compensatory growth by undernourished chickens and turkeys after return to an adequate diet has been reported previously (Auckland and Morris, 1971; Moran, 1979), but the metabolic changes that permit compensatory growth are not known. The effect of water restriction on body weight, feed consumption, and feed efficiency has been studied in broiler chickens by Kellerup et al. (1965). Comparison of present results with results from that study indicates that 50% water restriction may have a more severe impact on the body weight gain and feed consumption of the turkey poult than of the broiler chick and that the effect on feed effi-
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' ' Row means having a common superscript are not significantly different (P>.05). 1
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600 500400E 300 o 200 x
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150 Min. After TRH FIG. 5. Upper panel: plasma growth hormone (GH) response to administration of thyrotropinreleasing hormone (TRH) after 4 weeks on restricted feed or restricted water regimens (n = 10/group). Lower panel: plasma GH response to TRH administration one week after return to ad lib conditions (n = 5/group). Refer to legend of Figure 1 for explanation of symbols.
ciency may initially be more marked in the turkey (although the turkey appears to show greater improvement in feed efficiency as the period of restriction continues). However, such comparisons between these species can be only tentative because of experimental differences between studies. The influence of feed restriction on water consumption observed in the present study appears similar to the schedule-induced polydipsia reported to result from intermittent feeding of hungry monkeys (Schuster and Woods, 1966), mice (Palfai et al, 1971) and rats (Freed and Mendelson, 1977). Individual water consumption patterns of feed-restricted turkeys varied widely; some birds maintained essentially normal water consumption. All birds maintained normal water consumption during
In our experiments, injection of TRH increased circulating GH levels. A similar increase has been reported in chickens (Harvey et al, 1978b), ducks (Pethes et al, 1979), and certain mammals (Davis et al, 1976; Martin, 1976; Heuland et al, 1977). Our data also clearly show that the ability of TRH to elevate plasma GH levels in the turkey is enhanced by food restriction. The effects of undernutrition on the GH response to TRH has not been described in other birds. The results of such studies in mammals have been highly variable and make it difficult to draw analogies between our findings in the turkey and those obtained with TRH in other nutritionally-deficient species. Campbell et al. (1977) reported that TRH depressed GH levels in ad lib-fed, acutelystarved, or chronically-starved rats, while Shimoyama (1979) found an increased GH response to TRH in chronically-starved rats. In
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the first week of restricted feeding and returned to control levels after 1 week of ad lib feeding. These findings show that a restricted feeding program using intermittent feeding may result in management problems associated with excessive water consumption and excretion. The effect of undernutrition on the secretion of pituitary GH is not well understood. Circulating GH levels increase in several species of fasted monogastric animals but not in ruminants (Trenkle, 1976). In the rat, starvation depresses (Dickerman et al., 1969; Trenkle, 1970; Campbell et al., 1977) or elevates (Shimoyama, 1979) circulating levels of GH. Harvey et al. (1978a) observed a significant increase in plasma GH levels in immature chickens after a 12- or 24-hr fast. Scanes and Pethcs (1979) reported a similar response in the duck. The present results show that prolonged restriction (with the accompanying shift to meal-eating behavior) increases circulating GH levels in the immature turkey and that this increase is maintained for at least one week after returning to ad lib feed and water consumption. GH secretion is greatest in the birds suffering the most severe feed restriction; water intake per se does not appear to be related to the change in GH levels. These changes observed in the turkey are consistent with the known metabolic role of GH in other species, i.e., enhancement of amino acid uptake, nitrogen retention, glucose formation from glycogen and lipid catabolism. The elevated GH levels present after return to adequate nutrition may aid compensatory growth.
TURKEY GH AND FEED OR WATER RESTRICTION
In considering the action of TRH, an important question is whether this tripeptide is a true physiological releaser of GH. The fact that TRH elevates GH levels in humans only under pathological conditions argues strongly that TRH is not the physiological growth hormone-releasing hormone (GHRH) in this species. Synthetic ovine TRH has a marked effect on both in vivo and in vitro secretion of GH in the chicken (Harvey et al., 1978b), but no strong evidence has been obtained to indicate that TRH is GHRH in birds. Nair
et al. (1978) have partially characterized a bovine hypothalamic peptide that has pronounced GHRH activity at low doses in vivo and appears to specifically increase granular release from AP somatotrophs when infused into the portal vessel. In common with TRH, this peptide has a pyroglutamyl N-terminus. Further systematic investigation is needed to determine if this structural similarity confers on TRH a partial or minor role in regulating secretion of pituitary GH. Whether or not TRH participates in normal regulation of GH secretion, the demonstration that undernutrition increases circulating GH levels in the turkey and that this action is enhanced by TRH provides a useful new approach in examining the regulation of GH secretion in birds and in studying the role of GH in glucoregulation and compensatory growth. It must be emphasized, however, that the control mechanisms affecting GH secretion during chronic starvation or undernutrition may differ significantly from the mechanisms that operate in response to acute changes in nutrient intake. Wimpfheimer et al. (1979) have recently shown that the metabolic effects of a hormone may be altered by starvation in ways that depend upon the length of time without food. Starvation-induced changes in the metabolic rate of the rat initially result from decreased thyroid hormone levels; within 3 days, starvation additionally alters thyroid hormone activity by decreasing the tissue sensitivity to the hormone. In the chicken, prolonged fasting (65 hr) results in altered tissue sensitivity to insulin (Simon and Rosselin, 1978). Data presented here show that pituitary sensitivity to TRH stimulation is altered by undernutrition. Further research is required to determine the impact of such management practices as nutrient restriction on metabolic adaptation, and the effect of such adaptations on subsequent performance. ACKNOWLEDGMENTS
We thank C. L. Avery, S. R. McGuire, and S. R. Trost, Avian Physiology Laboratory, for their technical assistance during this study. We are also indebted to S. R. McGuire for preparation of the figures and to B. Weinland, Biometrical and Statistical Services, USDA, for statistical work. REFERENCES Auckland, J. N., andT. R. Morris, 1971. Compensatory
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humans, TRH stimulates GH release only under certain pathological conditions such as mental depression, acromegaly, and anorexia nervosa. In the latter condition, the increase in GH and its potentiation by TRH are clearly related to nutritional deficiency. Other pathological conditions in which there is reduced caloric intake also result in elevated GH levels (Brown et al., 1978). However, Vinik et al. (1974) have reported that the GH response to TRH is blunted in humans fasted for 36 hr. Many recent findings in the rat (Brown et al., 1978) indicate that these divergent responses in GH secretion to undernutrition and to TRH administration in underfed subjects are due primarily to a brain neurotransmitter deficiency that impairs the output of hypothalamic neurohormones regulating anterior pituitary (AP) function. In humans, those disorders associated with stimulation of GH release by TRH are frequently accompanied by impaired GH response to stimuli acting on the central nervous system. In rats, GH release induced by TRH is facilitated by surgical disconnection of the AP (Miiller et al., 1977) and by transplantation of the AP to the kidney capsule of the hypophysectomized rat (Udeschini et al., 1976). In the studies of Shimoyama (1979), in which the results of starvation and TRH injection in starved rats were similar to those reported here for the turkey, administration of chlorpromazene, thought to act on hypothalamic dopaminergic mechanisms regulating GH release, did not potentiate the increase in GH levels induced by starvation. The implication is that hypothalamic control of GH release in starved rats is abnormal. In our study, pituitary responsiveness to TRH returned to normal shortly after return to ad lib conditions, but basal GH secretion remained elevated in the previously-restricted birds. This may indicate that GH secretion is being influenced by undernutrition through multiple mechanisms.
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PROUDMAN AND OPEL Lee, P.J.W., A. L. Gulliver, and T. R. Morris, 1971. A quantitative analysis of the literature concerning the restricted feeding of growing pullets. Brit. Poultry Sci. 12:413-437. Martin, J. B., 1976. Brain regulation of growth hormone secretion. Pages 129—168 in Frontiers in neuroendocrinology. Vol. 4. L. Martini and W. F. Ganong, ed. Raven Press, New York, NY. Moran, E. T., Jr., 1979. Carcass quality changes with the broiler chicken after dietary protein restrictions during the growing phase and finishing period compensatory growth. Poultry Sci. 58:1257-1270. Miiller, E. E., A. E. Panerai, D. Cocchi, I. Gil-Ad, G. L. Rossi, and V. R. Olgiati, 1977. Growth hormone releasing activity of thyrotrophin-releasing hormone in rats with hypothalamic lesions. Endocrinology 100:1663-1671. Nair, R.M.G., C. de Villier, M. Barnes, J. Anatalis, and D. J. Wilbur, 1978. A bovine hypothalamic peptide possessing immunoreactive growth hormone releasing activity. Endocrinology 103:112-120. Palfai, T., C. L. Kutscher, and J. P. Symons, 1971. Schedule-induced polydipsia in the mouse. Physiol. Behav. 6:461-462. Pethes, G., C. G. Scanes, and P. Rudas, 1979. Effect of synthetic thyrotrophin releasing hormone on the circulating growth hormone concentration in cold and heat stressed ducks. Acta Vet. Acad. Sci. Hung. 27:175-177. Proudman, J. A., and B. C. Wentworth, 1978. Radioimmunoassay of turkey growth hormone. Gen. Comp. Endocrinol. 36:194-200. Proudman, J. A., and B. C. Wentworth, 1980. Ontogenesis of growth hormone in large and midget white strains of turkeys. Poultry Sci. 59:906—913. Scanes, C. G., and G. Pethes, 1979. Effect of insulin and fasting on the circulating growth hormone concentration in ducks. Acta Vet. Acad. Sci. Hung. 27:179-181. Schuster, C. R., and J. H. Woods, 1966. Scheduleinduced polydipsia in the rhesus monkey. Psychol. Rep. 19:823-828. Shimoyama, S., 1979. Studies on growth hormone secretion in starved rats under urethane anesthesia. Nippon Naibumpi Gakkai Zasshi 55:817—830. Simon, J., and G. Rosselin, 1978. Effect of fasting, glucose, amino acids and food intake on in vivo insulin release in the chicken. Horm. Metab. Res. 10:93-98. Spiller, R. J., R. W. Dorminey, and G. H. Arscott, 1973. The effects of intermittent watering of White Leghorn layers. Poultry Sci. 52:2088. (Abstr.) Trenkle, A., 1970. Effect of starvation on pituitary and plasma growth hormone in rats. Proc. Soc. Exp. Biol. Med. 135:77-80. Trenkle, A., 1976. Estimates of the kinetic parameters of growth hormone metabolism in fed and fasted calves and sheep. J. Anim. Sci. 43:1035—1043. Udeschini, G., D. Cocchi, A. E. Panerai, I. Gil-Ad, G. L. Rossi, P. G. Chiodini, A. Luizzi, and E. F. Muller, 1976. Stimulation of growth hormone release by thyrotrophin-releasing hormone in the hypophysectomized rat bearing an ectopic pituitary. Endocrinology 98:807-813.
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growth in turkeys: Effect of undernutrition on subsequent protein requirements. Brit. Poultry Sci. 12:41-48. Balnave, D., 1973. A review of restricted feeding during growth of laying-type pullets. World's Poultry Sci. J. 29:3 54-362. Barr, A. J., J. H. Goodnight, J. P. Sail, and J. T. Helwig, 1976. Statistical analysis systems. Statistical Analysis Systems Institute, Inc., Raleigh, NC. Brown, G. M., J. A. Seggie, J. W. Chambers, and P. G. Ettigi, 1978. Psychoendocrinology and growth hormone: A review. Psychoneuroendocrinology 3:131-153. Campbell, G. A., M. Kuroz, S. Marshall, and J. Meites, 1977. Effects of starvation in rats on serum levels of follicle stimulating hormone, luteinizing hormone, thyrotropin, growth hormone and prolactin; response to LH-releasing hormone and thyrotropin-releasing hormone. Endocrinology 100:580-587. Davis, S. H., K. M. Hill, D. L. Ohlson, and J. A. Jacobs, 1976. Influence of chronic thyrotropin-releasing hormone on secretion of prolactin, thyrotropin and growth hormone and on growth rate in wether lambs. J. Anim. Sci. 42:1233-1250. Dickerman, E., A. Negro-Vilar, and J. Meites, 1969. Effect of starvation on plasma GH activity, pituitary GH and GH-RF levels in the rat. Endocrinology 84:814-819. Freed, W. J., and J. Mendelson, 1977. Water-intake volume regulation in the rat: Schedule-induced drinking compared with water-deprivationinduced drinking. J.Comp. Physiol. 91:564—573. Harvey, S., P.M.M. Godden, and C. G. Scanes, 1977a. Plasma growth hormone concentrations during growth in turkeys. Brit. Poultry Sci. 18:547-551. Harvey, S., C. G. Scanes, A. Chadwick, and N. J. Bolton, 1978a. Influence of fasting, glucose and insulin on the levels of growth hormone and prolactin in the plasma of the domestic fowl (Gallus domesticus). J. Endocrinol. 78:501—506. Harvey, S., C. G. Scanes, A. Chadwick, and N. J. Bolton, 1978b. The effect of thyrotropin-releasing hormone (TRH) and somatostatin (GHRIH) on growth hormone and prolactin secretion in vitro and in vivo in the domestic fowl (Gallus domesticus). Neuroendocrinology 26:249—260. Harvey, S., C. G. Scanes, and T. Howe, 1977b. Growth hormone effects on in vitro metabolism of avian adipose and liver tissue. Gen. Comp. Endocrinol. 33:322-328. Heuland, L., S. G. Doelger, A. J. Tollerton, M. M. Lischko, and H. D. Johnson, 1977. Plasma growth hormone concentrations and cerebroventricular and jugular injection of thyrotropinreleasing hormone. Proc. Soc. Exp. Biol. Med. 156:422-425. Kellerup, S. U., J. E. Parker, and G. H. Arscott, 1965. Effect of restricted water consumption on broiler chickens. Poultry Sci. 4 4 : 7 8 - 8 3 . Krueger, K. K., J. A. Owen, C. E. Krueger, and T. M. Ferguson, 1977. Effect of feed or light restriction during the growing and breeding cycles on the reproductive performance of Broad Breasted White turkey males. Poultry Sci. 56:1566-1574.
TURKEY GH AND FEED OR WATER RESTRICTION
Vinik, A. I., W. J. Kalk, H. McLaren, and M. Paul, 1974. Impaired prolactin response to synthetic thyrotropin-releasing hormone after a 36 hour fast. Horm. Metab. Res. 6:499-501.
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Wimpfheimer, C , E. Saville, E. Danforth, Jr., and A. G. Burger, 1979. Starvation-induced decreased sensitivity of resting metabolic rate to triiodothyronine. Science 205:1272-1273.
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1981 Poultry Science 6 0 : 6 5 9 - 6 6 7 INTRODUCTION
Restricted feeding of turkeys and chickens during both the growing and laying periods has been studied extensively (Lee et al., 1971; Balnave, 1973; Krueger et al., 1977), but restricted water intake has received less attention (Kellerup et al., 1965; Spiller et al., 1973). Various restriction regimens have been proposed in an effort to reduce feed costs, control body weight, reduce mortality (particularly of turkeys), and improve reproductive performance. However, the effects of such restrictions on the physiology and metabolism of the growing bird are not well understood. Many regulatory factors operate simultaneously to control growth and metabolic processes. Growth hormone (GH), studied extensively in mammalian species but not in birds, has an important influence on growth and metabolism. Circulating GH levels in the growing turkey are positively correlated with growth rate (Harvey et al., 1977a; Proudman and Wentworth, 1980). Chicken GH stimulates in vitro lipolysis of avian adipose tissue and inhibits insulin-induced lipogenesis by the liver (Harvey et al., 1977b). Although Harvey et al. (1978a) have shown that plasma
GH levels are significantly elevated in the growing chicken during fasting, there have been no studies of the effects of prolonged feed or water restriction on GH secretion in the bird. The present study details these effects in the growing turkey poult. MATERIALS AND METHODS
Thirty Nicholas Large White male turkey poults, 4 weeks of age, were randomly divided into three groups' and placed in individual wire cages equipped with individual feeders and water bottles. A commercial growing diet (20% protein; 3000 kcal/kg ME) was fed throughout the experiment; tap water was warmed to room temperature before use. A 12 hr photoperiod was maintained (lights on at 0600 hr). A week pretreatment period, during which all birds received feed and water ad lib, allowed the birds to adjust to the cage environment. The experimental period commenced when the poults were 6 weeks old. The control group was fed ad lib, die first treatment group was restricted to 50% of the quantity of feed eaten by the controls on the previous day, and the second treatment group was restricted to 50% of die amount of water consumed by the
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ABSTRACT Both feed and water restriction of growing turkeys resulted in an increase in the basal levels of plasma growth hormone (GH). Restricted birds also showed an increased response to thyrotropin-releasing hormone (TRH) stimulation. These changes were significantly greater in feed-restricted birds than in the water-restricted birds. After return to ad lib conditions, basal plasma GH levels remained elevated above control levels in both previously restricted groups. However, the GH response to TRH stimulation returned to normal during this period. The increase in GH secretion during undernutrition is a metabolic adjustment consistent with the known role of GH in glucose, protein and fat metabolism. The elevated GH levels present after return to adequate nutrition may aid compensatory growth. Feed and water restriction were equally effective in limiting the growth of young turkey poults. Body weight gain and feed efficiency were severely affected during the first 3 weeks of restriction, but improved during the 4th week. Return to ad lib conditions resulted in compensatory growth and markedly improved feed efficiency in both restricted groups. Feed-restricted birds showed a significant increase in water consumption after 8 days of restriction. This polydipsia may result from intermittent feeding of hungry animals. Water consumption returned to normal after 1 week of ad lib feeding. Birds restricted in water consumption voluntarily limited their feed intake to a level only slightly higher than that of the feed-restricted group. When water was supplied ad lib, these birds immediately resumed normal feed consumption. (Key words: growth hormone, turkey, feed restriction, water restriction)
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RESULTS
The mean body weights of the control and restricted birds are shown in Figure 1. Birds fed and watered ab lib maintained a nearly-linear rate of growth throughout the experiment and gained an average of 5 3 9 g per week. Restricted birds were significantly lighter than controls after 6 days of restriction and remained lighter throughout the experiment. There was no significant difference between the mean body weight of the birds restricted in feed con-
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FIG. 1. Mean body weight of Large White male turkeys fed ad lib (•) or restricted in feed consumption (o) or water consumption (A) to 50% of ad lib intake for 4 weeks (n = 10/group). Restricted groups were then returned to ad lib conditions (arrow) for 1 week (n = 5/group). The bars represent ± SEM.
sumption vs. those restricted in water consumption at any of the ages studied. The restricted birds exhibited a very slow rate of gain during the first 3 weeks on the restricted regimens (177 g gain/bird/week) but grew at more than double this rate during the final week of restriction (390 g gain/bird/week). After return to ad lib feed and water, the restricted birds gained at a faster rate than the controls (940 g vs. 640 g gain/bird). The mean daily feed and water consumption for each group are presented in Figures 2 and 3, respectively. The feed consumption of both of the restricted groups was significantly less than that of the control group during the restriction period. Birds restricted in water consumption, but with access to feed ad lib, consumed only slightly more feed than the birds in the 50% feed restriction group. Return to ad lib feeding resulted in a dramatic one-day increase in feed consumption in the restricted feed group, followed by an immediate return to the feed
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controls on the previous day. The restricted feed group received water ad lib, and the water-restricted group was fed ad lib. Restrictions were imposed on the second day of the experiment and continued until the birds were 10 weeks and 1 day of age. At this time, 5 birds from each group were sacrificed for pituitary collection and the remaining 5 were given feed and water ad lib for 1 week. Daily feed and water consumption were measured for each bird; body weights were recorded weekly from 6 to 10 weeks of age, and at the end of the experiment. Blood samples were collected for GH assay by venipuncture into heparinized tubes at weekly intervals and at the end of the experiment. These samples were collected at the same time of day (1000 to 1100 hr), just before weighing and feeding. At 6 and 9 weeks of age, an additional blood sample was collected 2 hr after feeding. At 10 weeks and 1 day of age, all birds were challenged (before feeding) with a 2 /xg/kg dose of thyrotropin releasing hormone (TRH), injected ip in .9% NaCl. Blood samples were collected at 0, 30, 60, and 150 min after TRH administration. At the end of the experiment, the remaining birds were again challenged with TRH as above. All blood samples were refrigerated and centrifuged, and the plasma was stored at —20 C for GH assay. Plasma GH concentration was measured by a homologous radioimmunoassay (Proudman and Wentworth, 1978). The results were examined for statistical differences (P<.05) within time periods by analysis of variance and Duncan's new multiple range test. Significant increases or decreases in hormone levels between adjacent sampling periods, but within treatment groups, were indicated by a significant (P«.05) slope as determined by linear regression analysis. All statistical analyses were performed using the procedures of Barr et al. (1976).
TURKEY GH AND FEED OR WATER RESTRICTION
661
1
,
,
,
.
6
7
8
9
10
II
Age (weeks)
FIG. 2. Mean daily feed consumption of restricted and unrestricted birds. Refer to legend of Figure 1.
consumption pattern of the control birds. The water-restricted birds increased feed consumption to control levels on the first day of ad lib feeding. Water consumption patterns revealed dramatic differences among all groups. The feedrestricted birds maintained a pattern of water consumption similar to that of the controls for 8 days following the imposition of the restrictions; thereafter, and until the end of the restriction period, they consumed significantly more water than the controls consumed. Return to ad lib feeding resulted in a gradual decline in water consumption by this group to control levels. The water-restricted birds showed a dramatic increase in water intake for several days after return to ad lib conditions, but within 1 week the water consumption levels of these birds also matched those of the control birds. The feed efficiency of each of the groups is shown in Table 1. The restricted birds generally showed significantly poorer feed efficiency
than the controls during the first 3 weeks of restriction. During the 4th week, however, the feed efficiency of the restricted birds improved to equal that of the control group. During the final period (which included 1 day of restriction and 7 days ad lib), the feed efficiency of the previously restricted birds was significantly better than that of the controls; water-restricted birds showed a mean feed efficiency superior to that of the feed-restricted birds. Over the total experiment, feed efficiency did not differ significantly among the three groups. Restriction of feed or water intake resulted in a significant elevation of plasma GH levels within 1 week of imposing the restrictions (Fig. 4). Feed-restricted birds maintained plasma GH levels significantly higher than those of either of the other groups throughout the restricted period; GH levels in the waterrestricted birds exceeded control levels at 7 and 10 weeks of age. Return to ad lib conditions resulted in a significant increase in circulating GH levels in the previously water-restricted
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662
PROUDMAN AND OPEL
800
700
400
300
200
vh
7
8
9
10
II
Age (weeks)
FIG. 3. Mean daily water consumption of restricted and unrestricted birds. Refer to legend of Figure 1.
birds. Both restricted groups maintained higher GH levels than the controls even after feed and water consumption patterns had returned to normal. The decline in GH levels observed within groups during the experimental period is an expected change associated with increasing age and declining growth rate (Proudman and Wentworth, 1980). Measurement of pre-and postprandial GH levels (not shown) found no change in any
group 2 hr after feeding, either before or after imposition of the restricted regimens. The response to TRH administration, within 30 min of ip injection, was significant in all groups at both time periods studied. Release of GH in response to TRH stimulation was significantly greater in the restricted feed group than in the other groups at the end of the four-week period of restriction (Fig. 5, upper panel). Water-restricted birds showed a greater response
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"£ 500
TURKEY GH AND FEED OR WATER RESTRICTION TABLE 1. Weekly and total feed efficiency1
of restricted and unrestricted
663 turkeys
Feed efficiency2 Age (weeks)
Control
Restricted period: 6-7 7-8 8-9 9-10 Ad lib period: 10-11 Overall: 6-11
Restricted feed
Restricted water
± .067 a ± .056 a ± .026 a ± .102 a
.498 ± .017a .376 + .044b .340 ± .023b .620 ± .062a
.140 ± .060b .549 ± .108ab .383 ± .029b .739 ± .043a
.409 ± .027a
.671 ± .019b
.915 ± .055c
.536 ±.030a
.537 ± .017a
.542 ± .034a
.568 .684 .534 .709
Feed efficiency = gain (g)/feed consumed (g).
2
Mean + SEM; n = 10 during restricted period; n = 5 during ad lib period and overall.
than controls showed, but the differences between these groups were not statistically significant. One week after return to ad lib conditions, the response to TRH stimulation was the same for all groups (Fig. 5, lower panel). DISCUSSION
Restriction of the feed or water intake of
vf-,
7
8
9
10
II
Age (week)
FIG. 4. Mean plasma GH concentration of restricted and unrestricted birds. Refer to legend of Figure 1.
growing turkey poults had profound effects on growth, feed efficiency, and intake of the unrestricted nutrient, as well as a significant influence on GH secretion. Feed restriction and water restriction were equally effective in limiting the growth of young turkey poults. Body weight gain and feed efficiency were most severely affected during the first 3 weeks of restriction. Gain and efficiency (particularly of the water-restricted birds) substantially improved during the 4 weeks of restriction; such improvement may indicate some metabolic adaptation to the restricted regimen. However, verification of this improvement with a longer restriction period is necessary before any special significance can be attached to this observation. After 4 weeks of restriction, the return to ad lib conditions resulted in rapid growth characterized by very efficient utilization of feed. This compensatory growth by undernourished chickens and turkeys after return to an adequate diet has been reported previously (Auckland and Morris, 1971; Moran, 1979), but the metabolic changes that permit compensatory growth are not known. The effect of water restriction on body weight, feed consumption, and feed efficiency has been studied in broiler chickens by Kellerup et al. (1965). Comparison of present results with results from that study indicates that 50% water restriction may have a more severe impact on the body weight gain and feed consumption of the turkey poult than of the broiler chick and that the effect on feed effi-
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' ' Row means having a common superscript are not significantly different (P>.05). 1
PROUDMAN AND OPEL
664
600 500400E 300 o 200 x
100
200
100-
150 Min. After TRH FIG. 5. Upper panel: plasma growth hormone (GH) response to administration of thyrotropinreleasing hormone (TRH) after 4 weeks on restricted feed or restricted water regimens (n = 10/group). Lower panel: plasma GH response to TRH administration one week after return to ad lib conditions (n = 5/group). Refer to legend of Figure 1 for explanation of symbols.
ciency may initially be more marked in the turkey (although the turkey appears to show greater improvement in feed efficiency as the period of restriction continues). However, such comparisons between these species can be only tentative because of experimental differences between studies. The influence of feed restriction on water consumption observed in the present study appears similar to the schedule-induced polydipsia reported to result from intermittent feeding of hungry monkeys (Schuster and Woods, 1966), mice (Palfai et al, 1971) and rats (Freed and Mendelson, 1977). Individual water consumption patterns of feed-restricted turkeys varied widely; some birds maintained essentially normal water consumption. All birds maintained normal water consumption during
In our experiments, injection of TRH increased circulating GH levels. A similar increase has been reported in chickens (Harvey et al, 1978b), ducks (Pethes et al, 1979), and certain mammals (Davis et al, 1976; Martin, 1976; Heuland et al, 1977). Our data also clearly show that the ability of TRH to elevate plasma GH levels in the turkey is enhanced by food restriction. The effects of undernutrition on the GH response to TRH has not been described in other birds. The results of such studies in mammals have been highly variable and make it difficult to draw analogies between our findings in the turkey and those obtained with TRH in other nutritionally-deficient species. Campbell et al. (1977) reported that TRH depressed GH levels in ad lib-fed, acutelystarved, or chronically-starved rats, while Shimoyama (1979) found an increased GH response to TRH in chronically-starved rats. In
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300
the first week of restricted feeding and returned to control levels after 1 week of ad lib feeding. These findings show that a restricted feeding program using intermittent feeding may result in management problems associated with excessive water consumption and excretion. The effect of undernutrition on the secretion of pituitary GH is not well understood. Circulating GH levels increase in several species of fasted monogastric animals but not in ruminants (Trenkle, 1976). In the rat, starvation depresses (Dickerman et al., 1969; Trenkle, 1970; Campbell et al., 1977) or elevates (Shimoyama, 1979) circulating levels of GH. Harvey et al. (1978a) observed a significant increase in plasma GH levels in immature chickens after a 12- or 24-hr fast. Scanes and Pethcs (1979) reported a similar response in the duck. The present results show that prolonged restriction (with the accompanying shift to meal-eating behavior) increases circulating GH levels in the immature turkey and that this increase is maintained for at least one week after returning to ad lib feed and water consumption. GH secretion is greatest in the birds suffering the most severe feed restriction; water intake per se does not appear to be related to the change in GH levels. These changes observed in the turkey are consistent with the known metabolic role of GH in other species, i.e., enhancement of amino acid uptake, nitrogen retention, glucose formation from glycogen and lipid catabolism. The elevated GH levels present after return to adequate nutrition may aid compensatory growth.
TURKEY GH AND FEED OR WATER RESTRICTION
In considering the action of TRH, an important question is whether this tripeptide is a true physiological releaser of GH. The fact that TRH elevates GH levels in humans only under pathological conditions argues strongly that TRH is not the physiological growth hormone-releasing hormone (GHRH) in this species. Synthetic ovine TRH has a marked effect on both in vivo and in vitro secretion of GH in the chicken (Harvey et al., 1978b), but no strong evidence has been obtained to indicate that TRH is GHRH in birds. Nair
et al. (1978) have partially characterized a bovine hypothalamic peptide that has pronounced GHRH activity at low doses in vivo and appears to specifically increase granular release from AP somatotrophs when infused into the portal vessel. In common with TRH, this peptide has a pyroglutamyl N-terminus. Further systematic investigation is needed to determine if this structural similarity confers on TRH a partial or minor role in regulating secretion of pituitary GH. Whether or not TRH participates in normal regulation of GH secretion, the demonstration that undernutrition increases circulating GH levels in the turkey and that this action is enhanced by TRH provides a useful new approach in examining the regulation of GH secretion in birds and in studying the role of GH in glucoregulation and compensatory growth. It must be emphasized, however, that the control mechanisms affecting GH secretion during chronic starvation or undernutrition may differ significantly from the mechanisms that operate in response to acute changes in nutrient intake. Wimpfheimer et al. (1979) have recently shown that the metabolic effects of a hormone may be altered by starvation in ways that depend upon the length of time without food. Starvation-induced changes in the metabolic rate of the rat initially result from decreased thyroid hormone levels; within 3 days, starvation additionally alters thyroid hormone activity by decreasing the tissue sensitivity to the hormone. In the chicken, prolonged fasting (65 hr) results in altered tissue sensitivity to insulin (Simon and Rosselin, 1978). Data presented here show that pituitary sensitivity to TRH stimulation is altered by undernutrition. Further research is required to determine the impact of such management practices as nutrient restriction on metabolic adaptation, and the effect of such adaptations on subsequent performance. ACKNOWLEDGMENTS
We thank C. L. Avery, S. R. McGuire, and S. R. Trost, Avian Physiology Laboratory, for their technical assistance during this study. We are also indebted to S. R. McGuire for preparation of the figures and to B. Weinland, Biometrical and Statistical Services, USDA, for statistical work. REFERENCES Auckland, J. N., andT. R. Morris, 1971. Compensatory
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humans, TRH stimulates GH release only under certain pathological conditions such as mental depression, acromegaly, and anorexia nervosa. In the latter condition, the increase in GH and its potentiation by TRH are clearly related to nutritional deficiency. Other pathological conditions in which there is reduced caloric intake also result in elevated GH levels (Brown et al., 1978). However, Vinik et al. (1974) have reported that the GH response to TRH is blunted in humans fasted for 36 hr. Many recent findings in the rat (Brown et al., 1978) indicate that these divergent responses in GH secretion to undernutrition and to TRH administration in underfed subjects are due primarily to a brain neurotransmitter deficiency that impairs the output of hypothalamic neurohormones regulating anterior pituitary (AP) function. In humans, those disorders associated with stimulation of GH release by TRH are frequently accompanied by impaired GH response to stimuli acting on the central nervous system. In rats, GH release induced by TRH is facilitated by surgical disconnection of the AP (Miiller et al., 1977) and by transplantation of the AP to the kidney capsule of the hypophysectomized rat (Udeschini et al., 1976). In the studies of Shimoyama (1979), in which the results of starvation and TRH injection in starved rats were similar to those reported here for the turkey, administration of chlorpromazene, thought to act on hypothalamic dopaminergic mechanisms regulating GH release, did not potentiate the increase in GH levels induced by starvation. The implication is that hypothalamic control of GH release in starved rats is abnormal. In our study, pituitary responsiveness to TRH returned to normal shortly after return to ad lib conditions, but basal GH secretion remained elevated in the previously-restricted birds. This may indicate that GH secretion is being influenced by undernutrition through multiple mechanisms.
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