Strain Differences in Serum Corticosterone, Growth Hormone, and Thyroxine of Young Chicks Reared in Two Different Brooding Temperature Environments1

Strain Differences in Serum Corticosterone, Growth Hormone, and Thyroxine of Young Chicks Reared in Two Different Brooding Temperature Environments1 T. R. SCOTT and K. W. WASHBURN Department of Poultry Science, University of Georgia, Athens, Georgia 30602 (Received for publication February 2, 1984)

1985 Poultry Science 64:212-220 INTRODUCTION Rearing y o u n g chickens at lower t h a n r e c o m m e n d e d environmental t e m p e r a t u r e s or a b r u p t l y exposing newly h a t c h e d chicks t o cold reduces growth as evidenced b y m e a s u r e m e n t s of absolute b o d y weights, gains, and muscle g r o w t h ( H u t s o n et al, I 9 6 0 ; Sagher, 1 9 7 5 ; R e n w i c k and Washburn, 1 9 8 2 ) . However, little is k n o w n a b o u t t h e n e o n a t a l responses t o cold exposure of such g r o w t h influencing h o r m o n e s as corticosterone (B), g r o w t h h o r m o n e ( G H ) , and t h y r o x i n e ( T 4 ) . A s p a r t of t h e a d a p t a t i o n m e c h a n i s m , circulating levels of B were increased in older p o u l t r y with exposure to cold (Brown and Nestor, 1 9 7 3 ; El Halawani et al, 1 9 7 3 ; Buckland et al, 1 9 7 4 ; Nir et al, 1 9 7 5 ; Nestor and Bacon, 1982), b u t prolonged influences of corticosteroids resulted in a g r o w t h depression of chicks (Davison et al, 1 9 7 9 ; Harvey and Scanes, 1 9 7 9 ) . Also, a d r e n o c o r t i c o t r o p i n , cor-

1 Supported by State and Hatch funds allocated to the Georgia Agricultural Experiment Stations of the University of Georgia.

212

tisol, and cold e x p o s u r e have p r o d u c e d changes in t h e b o n e c o m p o s i t i o n of y o u n g female chickens t h a t d o n o t reflect a state of growth (Siegel and Latimer, 1 9 7 0 ) . G r o w t h h o r m o n e has been positively correlated with relative g r o w t h o f p o u l t r y (Harvey et al, 1977a, 1 9 7 9 ) , and its influence o n t h e increased p r o d u c t i o n of ribonucleic acid and p r o t e i n in various tissues was observed b y Scanes et al. ( 1 9 7 5 ) . Harvey et al. ( 1 9 7 7 b ) reported decreases in circulating levels of GH in chickens after exposure to cold, b u t a n o t h e r s t u d y with d u c k s (Pethes et al, 1979) f o u n d n o effect of cold o n this h o r m o n e . Cold exposure has been f o u n d t o cause an elevation of T 4 in p o u l t r y (Kiihn and N o u w e n , 1 9 7 8 ; Bobek et al, 1 9 8 0 ; H e r b u t e et al, 1 9 8 3 ) , which is generally associated with t h e need for increased calorigenesis. T h y r o x i n e also stimulates muscle g r o w t h of h y p o t h y r o i d chickens (King and King, 1 9 7 3 ; 1976) and is positively and strongly correlated w i t h b o d y weight in growing chicks (Kiihn et al, 1982). T h e ability of a chick t o grow in an env i r o n m e n t is influenced b y its genetic composition. Renwick ( 1 9 8 1 ) found increased expression of genetic variation associated with weight gain when chicks from a r a n d o m b r e d

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ABSTRACT Chicks from a nongrowth-selected randombred population (AC) and from various growth-selected broiler strain crosses (SC) were reared in two brooding temperature environments (26.7 and 32.2 C) for a period of 2 weeks. Strain and temperature effects on weight gain and serum corticosterone (B), growth hormone (GH), and thyroxine (T 4 ) were measured at 1, 7, and 14 days of age. Brooding at 26.7 C increased mortality and reduced weight gain. Serum corticosterone levels were significantly higher in chicks brooded at 26.7 C on Days 7 and 14, whereas statistically higher levels of GH were observed only at 1 day of age for chicks brooded at 26.7 C. The T 4 levels were also significantly higher in 1-day-old chicks brooded at 26.7 C, but at 7 and 14 days of age T 4 levels were significantly higher in the chicks brooded at 32.2 C. The magnitude of the effect of brooding temperatures on responses was related to the strain of chick. Weight gain of all chicks brooded at 32.2 C was significantly correlated with serum levels of B, GH, and T 4 , but only the correlation between gain and B level of 26.7 C brooded chicks was significant. Serum corticosterone and GH were negatively associated with gain, whereas a positive relationship existed between gain and T 4 levels. Among AC chicks, gain was negatively correlated with B levels and positively correlated with GH levels. There was a positive correlation between gain and T 4 levels of the strain cross with the smallest body weight whereas the gain of the high weight strain crosses was correlated to both T 4 (positive) and B (negative) levels. (Key words: genetics, corticosterone, growth hormone, thyroxine, brooding temperature)

STRAIN DIFFERENCES AND BROODING TEMPERATURE

MATERIALS AND METHODS

Chicks were hatched from eggs that had been obtained from either a nongrowth-selected randombred population, the Athens-Canadian (AC) randombred population (Hess, 1962), or from growth-selected commercial broilers. The commercial broiler eggs were produced from five different strain crosses (SCI, SC2, SC3, SC4, SC5). In four of the five crosses the genetic background of the males differed from that of the females, which were from the same broiler strain. Eggs from all groups were set at the same time in the same incubator, and no differences were observed between genetic groups in hatching time. Upon hatching, chicks were wingbanded, weighed, and distributed within genotype into

two brooding temperature environments. These environments consisted of Petersime battery brooder units housed in light- and temperat u r e - c o n t r o l l e d e n v i r o n m e n t a l chambers. Brooding temperatures under the heated compartment of the batteries used were 26.7 and 32.2 C. The battery brooder unit heated to 26.7 C was housed in an environmental chamber that cycled from 13 to 24 C through a 24-hr period, while the unit heated to 32.2 C was housed in a chamber that cycled from 24 to 35 C through the same period. The brooding temperatures were maintained by frequent checking of the temperature and, when needed, adjustment of the individual heating units within the batteries. These brooding temperatures were held constant throughout the course of the study. The chicks were provided the University of Georgia unmedicated starter diet and water ad libitum in the heated area under the brooder hover during the first 7 days. From 7 to 14 days, feed and water were provided ad libitum in battery feed and water troughs. Twenty chicks per genotype and brooding temperature combination were weighed at 1, 7, and 14 days of age. Blood sampling of these chicks at 1 and 7 days of age was by decapitation with immediate collection of blood into 13 X 10-mm culture tubes, and at 14 days of age blood was obtained by cardiac puncture. Collected blood was allowed to clot, and serum was separated by centrifugation, frozen, and later assayed for serum B, GH, and T 4 concentrations. Quantitation of serum B was carried out according to a modification of the Endocrine Sciences radioimmunoassay for B (Endocrine Sciences, 1972) described by Satterlee et al. (1980). An assay buffer of phosphate-buffered saline (pH 7.4) with .1% gelatin was substituted for a borate buffer. The turkey GH radioimmunoassay of Proudman and Wentworth (1978), which has been further described by Burke and Marks (1982), was used to measure serum GH concentrations. Serum T 4 was determined with a commercially purchased kit from Antibodies Inc. (Davis, CA 95616). The experiment was a randomized block design (blocking on battery deck level); genotype and brooding temperatures were the main effects of interest. Data were subjected to analysis of variance within sampling times, and further separation of means was carried out on genotype means.

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population were reared at 26.7 C, and Renwick and Washburn (1982) observed strain differences in weight gain among young broilers brooded at this same temperature. Genetic influences may also affect the circulating levels of B, GH, and T 4 in poultry. Line differences in the corticosterone response to adrenocorticotropin injections, cold and heat exposure, and social stress have been reported for older poultry (Gross and Colmano, 1971; Brown and Nestor, 1973; Edens and Siegel, 1975; Nestor and Bacon, 1982). Circulating levels of GH have been shown to differ between strains of chickens (Harvey et al., 1979) and among various lines of poultry that differed in growth rate (Proudman and Wentworth, 1980; Burke and Marks, 1982, 1984), although a relationship between increased growth and high levels of growth hormone was not shown. Genetic variation in T4 levels of neonatal chickens expressed as a result of thyrotropin injections (Bowen and Washburn, 1982) and line differences in selected populations of chickens (May and Marks, 1983) and Japanese quail (Burke and Marks, 1984) have been shown. The objectives of this study were to compare the growth and hormonal responses to reduced temperature brooding of growth-selected broiler strains with a nonselected randombred control and to determine if reduced temperature brooding results in the expression of additional genetic differences not observed under more normal brooding conditions.

213

SCOTT AND WASHBURN

214

RESULTS AND DISCUSSION

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The mean gain for the chicks brooded at 26.7 C as a percentage of the value for the group brooded at 32.2 C was 29% for the first day; 79% during Days 0 to 7 and 93% during Days 7 to 14 (Table 1). This is in agreement with previous studies (Renwick and Washburn, 1982), which have shown that the depression in body weight in young chicks brooded at 26.7 C is more evident during the first than the second week of cool temperature brooding. Mortality. Percent mortality was higher among chicks brooded at 26.7 C than for those brooded at 32.2 C (Table 2). This is in agreement with the results of Renwick and Washburn (1982). The percent mortality of SC2 chicks brooded at 26.7 C was much higher than

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Body Weight Gain. Reduced temperature brooding (26.7 C) for 1, 7, or 14 days resulted in a significant depression of body weight gains (Table 1). There were body weight differences between the different strains within the 32.2 C temperature brooding environment. As expected, the gain of the unselected AC population was significantly less than that of the broiler strain crosses for all time periods. In general, the gain of SC2 was less than that of the other strain crosses. There were differences between populations in the magnitude of the depression in weight gain by brooding at 26.7 C. These population by temperature interactions were statistically significant for the periods 0 to 1 and 0 to 7 days. Although these interactions reflected the differences in response of these populations to the 26.7 C brooding temperature, smaller body size was apparently not associated with these differences in response. For example, the 0 to 7-day gain in the 26.7 C environment for the population with the smallest size (AC) was 88% that of birds in the 32.2 C environment compared to 69% for the strain with the greatest gain (SC5). The AC chicks in both the 26.7 and 32.2 C temperature environments lost weight the first day after hatching, and the gains at 0 to 7 days and 7 to 14 days were lower for both groups than expected from one study (Marks, 1981) but are in general agreement with those of Renwick and Washburn (1982). No significant strain by temperature interactions were found for any growth data on Day 14, suggesting that growth differences observed at the end of the second week were more indicative of the expression of varying genetic potentials for growth, regardless of the brooding temperature environment.

STRAIN DIFFERENCES AND TABLE 2. Percent mortality from 0 to 14 days of age of chicks brooded at 26.7 and 32.2 C

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The B levels were increased by brooding at 26.7 C in all populations, but the magnitude of the increase differed between populations. One-day-old AC chicks had significantly greater B levels than strain cross broilers when brooded at either temperature, and at Day 7 the B levels of the AC population were also higher in both temperature groups. By 14 days of age, the B

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SCOTT AND WASHBURN

levels of GH (Burke and Marks, 1984). Thus, higher GH levels in circulation were not necessarily indicative of greater growth. Our results with young chicks from different broiler strains agree with such a conclusion. There was variation between populations in the magnitude of the differences of GH levels in the two environments, but these differences were not consistent with time. For example, at 7 days the GH levels of SC2 in the 26.7 C environment was 81%, and that for SC5 was 176% of the comparable strain in the 32.2 C environment, However, at 14 days the values were 117% for SC2 and 98% for SC5. Thyroxine. A significant effect of brooding temperature on serum T4 was observed at each of the three sampling times, but this effect was different for the various ages. The T4 levels of reduced temperature brooded chicks were significantly higher at 1 but lower at 7 and 14 days of age (Table 5). Cold exposure generally causes an elevation of circulating T 4 levels (Kiihn and Nouwen, 1978; Bobek et al., 1980; Herbute et al., 1983), but in the present study any cold elevating influence on serum T 4 was observed only at 24 hr. The significant temperature differences in circulating T4 levels observed on Days 7 and 14 may reflect the differences in body weight and gain at these ages. Thyroxine is known to influence muscle growth of chickens (King and King, 1973, 1976), and it has been significantly correlated with body weight in growing chicks (Kiihn et al., 1982). Overall genetic differences in serum T4 concentrations among genotypes were observed on Day 1 but not at the two other ages. When examined within temperature groups, significant strain differences were found on Days 1 and 7. One-day-old AC chicks brooded at 32.2 C had statistically greater T 4 values than all strain cross neonates, but some commercial broiler strain crosses exposed to the 26.7 C brooding temperature had levels almost as high as the AC chicks. Reduced temperature brooding appears to have accentuated the expression of genetic differences in serum T4 of these neonates. By 7 days of age, strain differences among chicks brooded at 26.7 C were not significant, and the genetic differences in serum T 4 observed were among the chicks brooded at 32.2 C. In fact, SC5 had the highest T 4 levels while that of the AC population was intermediate. May and Marks (1983) noted a similarity in serum T 4 levels of selected and non-

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levels of the AC population were similar to those of strain cross broiler chicks. There were no differences between broiler strains that were consistent over the three ages. Genetic differences in the magnitude of the corticosterone response of various poultry stocks have been reported (Gross and Colmano, 1971; Brown and Nestor, 1973; Edens and Siegel, 1975; Fisinin and Kravchenko, 1977; Davison et al, 1980; Freeman and Flack, 1980; Nestor and Bacon, 1982; Satterlee et al., 1982), and some studies have found genetic differences in resting levels of corticosterone (Davison et al, 1980; Flack and Freeman, 1983) while others have not (Edens and Siegel, 1975; Satterlee and Gildersleeve, 1983). The results of our study show that genetic influence on both resting and cold stress response levels of serum B in young chicks was present, but this influence disappeared by the time chicks reached 14 days of age. Growth Hormone. Harvey et al. (1977b) observed lower circulating GH levels after chickens had been exposed to cold for a short time. Brooding neonates in the current study at 26.7 C for 24 hr resulted in significantly higher concentrations of serum GH. Continued exposure to the lower brooding temperature did not significantly affect the overall GH levels at 7 and 14 days of age (Table 4), although the mean values for Days 7 and Days 14 were higher in the 26.7 C group. As noted earlier, 26.7 C temperature brooding reduced weight gains of these chicks at all ages (Table 1). Elevated plasma levels of GH have previously been observed in chickens whose growth was depressed (Davison et al., 1979; Harvey and Scanes, 1979). In examining genetic influences on serum GH levels, differences were observed among all genotypes at 1 day of age (Table 4). Brooding at 26.7 C appeared to cause a greater expression of the genetic differences than brooding at 32.2 C. However, by 7 and 14 days of age, only the extremely large differences between AC chicks and the broiler strain crosses were observed. This situation was present when combined, as well as temperature-separated, data were examined at both older ages. Such extreme differences in GH levels between this randombred population and commercial broilers have been reported from 1 to 8 weeks of age (Burke and Marks, 1982); and when compared with a large body weight line, a control line of Japanese quail had as high or higher circulating

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TABLE 6. Phenotypic correlations between weight gain and serum hormones across strain crosses and •within brooding temperatures

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STRAIN DIFFERENCES AND BROODING TEMPERATURE

Based on t h e within-strain cross correlations of gain with B and GH, selection at y o u n g ages involving any one of these t h r e e traits would m o r e likely affect t h e o t h e r t w o if t h e selection was carried o u t w i t h A C chicks. A m o n g strain cross broilers, however, selection for either gain or serum T4 levels in y o u n g chicks would probably result in c o n c o m i t a n t changes in t h e nonselected traits.

ACKNOWLEDGMENTS T h e a u t h o r s would like to t h a n k Samuel Bowen, Rachel Peavey, and Pamela Stewart for their technical assistance.

REFERENCES Bobek, S., J. Niezgoda, M. Pietras, M. Kacinska, and Z. Ewy, 1980. The effect of acute cold and warm ambient temperature on the thyroid hormone concentration in blood plasma, blood supply, and oxygen consumption in Japanese quail. Gen. Comp. Endocrinol. 40:201-210. Bowen, S. J., and K. W. Washburn, 1982. Genetic variation in thyroxin response to TSH in Athens-Canadian randombred chicks. Poultry Sci. 61:1422. (Abstr.) Brown, K. I., and K. E. Nestor, 1973. Some physi-

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levels of this t h y r o i d h o r m o n e . Kiihn et al. ( 1 9 8 2 ) f o u n d a strong positive correlation b e t w e e n b o d y weight and T4 in growing chicks, and o u r results also indicate t h a t increases in b o d y weight are similarly associated with T 4 levels. Significant correlations, across t h e three sampling periods, b e t w e e n serum T 4 and weight gain were found in strain crosses grouped into high (HSC) and low b o d y weight gain (SC2) classes (Table 7). However, AC chicks (which exhibited t h e least weight gain) showed n o correlation b e t w e e n T4 and gain. T h e HSC chicks also had a significant correlation b e t w e e n weight gain and B, b u t an even greater negative correlation b e t w e e n these t w o traits was found in A C chicks. Circulating levels of B have been reported t o be inversely related with b o d y weight in p o u l t r y (Nestor and Bacon, 1 9 8 2 ; Satterlee et al, 1982), and o u r results across strains and b r o o d i n g t e m p e r a t u r e s agree with these previous findings. Levels of GH in t h e serum of A C chicks were positively correlated with gain, b u t n o significant correlations were observed for t h e strain cross broilers. Studies in t h e past with chickens and t u r k e y s have f o u n d significant negative correlations between b o d y weight and GH levels (Harvey et al, 1977a, 1 9 7 9 ) .

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