Plasma Concentrations of Corticosterone and Thyroid Hormones in Broilers Provided Various Lighting Schedules1

Plasma Concentrations of Corticosterone and Thyroid Hormones in Broilers Provided Various Lighting Schedules1 J. A. RENDEN, R. J. LIEN, S. S. OATES, and S. F. BILGILI Department of Poultry Science, Alabama Agricultural Experiment Station, Auburn University, Alabama 36849 ABSTRACT The purpose of this study was to measure plasma corticosterone and thyroid hormone concentrations in broilers exposed to various photoschedules. Day-old male broilers were placed on litter floors in light-controlled chambers. Four chambers were randomly assigned to each of four light treatments: 1) 23 h light (L):l h dark (D) from 1 to 56 d of age (designated extended, E); 2) 1L:3D from 1 to 56 d (intermittent, I); 3) 6L:18D from 1 to 14 d and 1L:3D from 15 to 56 d (brief-I, BI); and 4) 6L:18D from 1 to 14 d and 23L:1D from 15 to 56 d (brief-E, BE). Blood samples were collected 0,4, and 20 h after lights-on (1200 h) at 13,41, and 55 d of age. Corticosterone concentration did not differ among light treatments or collection times and was decreased at 41 d compared with 13 d (.65 vs 2.11 ng/mL). Triiodothyronine (T3) increased and thyroxine (T4) decreased with age. At 13 d, there were light treatment by sampling time interactions for T3 and T4. Plasma T3 was elevated in Treatments BI (3.11 ng/mL) and BE (3.40 ng/mL) compared with Treatments E (2.39 ng/ mL) and I (2.30 ng/mL) at 0 h; the former two treatments showed decreased T3 concentrations at 4 and 20 h compared with 0 h. Plasma T4 showed reciprocal changes to T3. There were no differences in T3 or T4 for light treatments or sampling times at 41 and 55 d. The light treatments did not cause severe stress, and elevated T3 concentrations in Treatments BI and BE at 13 d were most likely associated with feeding during the dark period. (Key words: light, broiler, corticosterone, triiodothyronine, thyroxine) 1994 Poultry Science 73:186-193

reduced light may be associated with metabolic changes during darkness. Broiler livability and leg soundness can Thyroid hormones are required for be improved by lighting programs that normal growth in chickens (Snedecor and restrict early growth (Classen and Riddell, Mellen, 1965; Hendrich and Turner, 1966), 1989; Classen el al, 1991; Renden et al, influence metabolic rate (reviewed by 1991). Maximum growth generally occurs May, 1989), and have been used as with continuous light (Morris, 1967); how- indicators of stress response (Wodzickaever, continuous light has been shown to Tomaszewska et al, 1982). Reduction of be stressful to growing broilers (Buckland, plasma thyroid hormone concentrations during stress is related to elevated plasma 1975; Buckland el al, 1976; Freeman et al, corticosterone (Williamson and Davison, 1981a). Classen et al. (1991) suggested that 1987; Decuypere and Kuhn, 1988; Klandorf improvements in the skeletal system with et al, 1988). The purpose of the current study was to examine concentrations of thyroid hormones and corticosterone in broilers provided near-continuous or reReceived for publication June 21, 1993. stricted fight programs. Live performance Accepted for publication September 29, 1993. of birds in the present study has been 1 Alabama Agricultural Experiment Station Numreported previously (Renden et al, 1991). ber 12-933538. INTRODUCTION

186

CORTICOSTERONE AND THYROID HORMONES

MATERIALS AND METHODS Experimental Design Specific experimental details were described by Renden et dl. (1991). Light treatments were 1) 23 h light (L):l h dark (D) from 1 to 56 d of age (extended, E); 2) 1L:3D repeated from 1 to 56 d (intermittent, I); 3) 6L:18D from 1 to 14 d and 1L:3D repeated from 15 to 56 d (brief-intermittent, BI); and 4) 6L:18D from 1 to 14 d and 23L:1D from 15 to 56 d (brief-extended, BE). The light period began at 1200 h (0 h), and light intensity was 5 lx. Each light treatment had four replicate chambers with 100 chicks (Ross x Cobb) in each chamber. Birds were provided ad libitum access to feed and water. All diets met or exceeded NRC (1984) requirements. Collection of Blood Samples Blood samples were collected from five randomly chosen and different chicks per chamber at 0 (1200 h), 4 (1600 h), and 20 h (0800 h) after lights-on at 13,41, and 55 d of age. The sequence of chambers sampled was randomized, and birds were selected at random throughout each chamber with a minimum amount of disturbance. Blood was collected into tubes containing 25 fiL of a saturated EDTA solution following decapitation on Day 13. On Days 41 and 55, 2 to 3 mL of blood was collected from the brachial vein into EDTA-coated syringes. Individual birds were caught, sampled within 1 min, and marked with dye to preclude subsequent sampling. Sampling from each chamber was completed within 6 min. Plasma samples were stored frozen (-20 C) for later determination of corticosterone, triiodothyronine (T3), and thyroxine (T4) concentrations.

2

ICN Biomedicals, Inc., Costa Mesa, CA 92626. 3Sigma Chemical Co., St. Louis, MO 63178-9916. Fisher Scientific, Pittsburgh, PA 15219. 5 Antibodies, Inc., Davis, CA 95617. 6 Hycor Biomedical, Inc., Ventrex Division, Portland, ME 04104. 7 Eastman Kodak Clinical Diagnostics, Rochester, NY 14650. 4

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Radioimmunoassay of Corticosterone A commercial kit2 was modified for use with chicken plasma. Commercial standards (80 itL) were diluted with charcoalstripped broiler plasma (20 /tL). Stripped plasma (20 fiL, for zero binding), an unstopped broiler plasma pool (20 fiL, control), and unknown samples (20 jtL) were diluted with commercial steroid diluent (80 /tL). All tubes except total count tubes contained a 100-fiL (20% plasma-based) sample. Standard curves ranged from .1 ng/mL (84% binding) to 4.0 ng/mL (17% binding). Slopes of log-logit transformed curves for the unstopped plasma pool diluted with stopped plasma (-1.91) and standards (-1.97) were not different (P > .05). Mean (±SE) recovery of corticosterone added to the unstopped pool was 112.8 ± 3.1%. Sensitivity (concentration at 2 SD from zero binding) was .02 ng/mL. Withinand between-assay CV were 8.2 and 10.0%, respectively. Radioimmunoassay of Triiodothyronine Barbltal-Bovlne Serum Albumin Buffer. The buffer was prepared according to the method of May (1978) except that it contained 2.5 rather than 1 g BSA3/L, and 1.0 g/L sodium azide4 was added. Assay Components. Nonspecific binding (NSB) solution contained 4 fiL rabbit y globulin5/mL barbital-BSA buffer. Primary antibody solution was prepared by adding rabbit T3 antisera6 to NSB solution in an amount that resulted in 45% binding of I25i-T3. Secondary antibody solution contained 60 nL goat anti-rabbit y globulins/ mL barbital-BSA buffer. The i25i-T37 was diluted in barbital-BSA buffer to yield 120,000 cpm/mL. Dispensing solution c o n t a i n e d 2.00 mg 8 - a n i l i n o - l naphthalenesulfonic acid3 (ANSA)/mL barbital-BSA buffer. Standards. Standards were prepared by dissolving 3,3',5-triiodo-L-thyronine3 in .1% NaOH and diluting with barbital-BSA buffer to a concentration of 640 ng/mL. Dilution with stripped plasma produced the first standard with a concentration of 6.4 ng/mL. The remaining standards (3.2,1.6, .8, .4, and .2 ng/mL) were prepared through

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RENDEN ET AL.

serial dilutions using stripped plasma. Stripped plasma was used for the zero standard. Stripped plasma was used in zero binding tubes and to prepare standards, because factors in bird plasma other than thyroid hormone crossreact in these assays and may cause overestimation of thyroid hormone concentrations unless thyroid hormone-free plasma is used in standards (Lien, 1988; Burke et ah, 1990). Assay Procedure. Aliquots (100 /xL) of samples, standards, and stripped and unstripped plasma pools were dispensed at room temperature into borosilicate tubes with 250 /xL dispensing solution. A 100-/xL aliquot of the unshipped pool was used in NSB tubes. Following sampling, tubes were placed on ice, and 250 /xL of both trace and primary antibody solutions were added. A 250-iiL aliquot of NSB solution was added to NSB tubes in place of the primary antibody. Tubes were vortexed then incubated at room temperature for 20 h. After the first incubation, the tubes were returned to ice, and 250 /xL of secondary antibody solution were added. Tubes were vortexed then incubated at 4 C for 24 h. After the second incubation, tubes were centrifuged at 1,200 x g for 30 min, and the supernatant was poured off. Tubes were allowed to dry prior to counting in a gamma counter.2 A customized program was used to plot the standard curve and generate sample T3 concentrations. Assay Validation. The standard curve ranged from .2 ng/mL (73% binding) to 6.4 ng/mL (12% binding). Slopes of log-logit transformed curves for the diluted pool (-2.46) and standards (-2.16) did not differ. Recovery of T3 added to the unshipped pool was 106 ± 7%. Sensitivity was .1 ng/ mL. Within- and between-assay CV were 7.0 and 9.4%, respectively.

BSA buffer. The I25T_T47 w a s diluted in barbital-BSA buffer to yield 100,000 cpm/ mL. Dispensing solution contained 1.66 mg ANSA/mL barbital-BSA buffer. Standards. Standards were prepared in a manner similar to that described for the T3 assay, but T43 was used at concentrations of .5, 1, 2, 4, 8, 16, and 32 ng/mL. Assay Procedure. The T4 assay procedure was identical to that of T3 with the exception of component volumes. The following volumes were used per tube as appropriate: samples, standards, stripped and unshipped pools, 50 /xL; dispensing solution, 300 /xL; trace solution, 200 /xL; primary antibody solution, 300 tiL; NSB solution, 300 11L; secondary antibody solution, 200 tiL. Assay Validation. The standard curve ranged from .5 ng/mL (86% binding) to 32 ng/mL (15% binding). Slopes (-2.06) of loglogit transformed curves for the diluted pool and standards were similar. Recovery of T4 added to the unshipped pool was 99 ± 5%. Sensitivity was .2 ng/mL. Within- and between-assay CV were 8.3 and 6.5%, respectively. Statistical Analysis Hormone data were analyzed within ages as a completely randomized design with repeated measures, with light treatment and time of sampling as main effects (Gill, 1981). Chamber was considered as the experimental unit. Repeated measures analysis of variance of the General Linear Models procedure of SAS® software (SAS Institute, 1988) was used with the following model: Yijk = /i + L; + c(i)j + Tk + (LT)jk + eijk

where i = 1, 2, 3, 4 treatments; j = 1, 2, 3, 4 chambers per treatment; k = 1, 2, 3 sample Radioimmunoassay of Thyroxine times; Y^ = plasma hormone concentration; Assay Components. The NSB solution ii = population mean; L, = effect of light contained 3.75 /*L rabbit 7 globulin/mL treatment; c(i)j = error term (12 df) for light barbital-BSA buffer. Primary antibody solu- treatment; Tk = effect of sampling time; and tion was prepared by adding rabbit T4 e^ = error (residual) term (24 df) for antiserums to NSB solution in an amount sampling time and light treatment by that resulted in 30% binding of 125I-T4. sampling time interaction. Samples colSecondary antibody solution contained 55 lected at 1200 h (0 h) were used to test age /xL goat anti-rabbit 7 globulin/mL barbital- effects using the following model:

CORTICOSTERONE AND THYROID HORMONES Y

ijk

=

H + Lj + cm + Ak + (LA)* + eijk

with a description similar to that for the previous model except k = 1,2,3 wk of age; and Ak = age effect. Main effect means were separated with Tukey's test. RESULTS AND DISCUSSION Concentration of corticosterone did not differ among light treatments or time of collection and was decreased at 41 and 55 d of age compared with 13 d [.65 and .60 vs 2.11 ng/mL, respectively; Table 1]. The values of plasma corticosterone concentration reported in the present study are similar to those reported by Scott et al. (1983) and Mench (1991). There is limited evidence to indicate that corticosterone in chicks expresses a circadian rhythm. Freeman and Flack (1980) and Freeman et al. (1981a) reported that plasma corticosterone concentration did not vary with time of day with a photoschedule of 12L:12D; however, Siegel et al. (1976) stated that plasma corticosterone began to increase 2 h before light on and peaked 2 h prior to light off under the same photoschedule. Smoak and Birrenkott (1986) found that corticosterone concentration peaked (>2.0 ng/mL) 30 min after lights on and gradually decreased during a light schedule of

189

23L:1D. Plasma corticosterone has been shown to decline with age in Light Sussex chicks (Freeman et al, 1981b). Regarding the influence of light on plasma corticosterone concentrations, Buckland et al. (1976) reported that plasma corticoids were higher in broilers grown with continuous light compared with intermittent lighting programs. Freeman et al. (1981a), however, did not find a difference in plasma corticosterone between chicks grown with continuous or 12L:12D light schedules, although the chicks given continuous light were considered stressed because of adrenal hypertrophy and elevated plasma free fatty acid concentrations. In the present study, there were no significant differences among light treatments for plasma corticosterone. Feed restriction in chicks has been shown to be a potent stressor (Freeman et al, 1980, 1981b). The light treatments I, BI, and BE have been shown to reduce feed consumption compared with Treatment E (Renden et al, 1991), however the three former light treatments do not seem to act as a stressor as indicated by corticosterone concentration. Consequently, restriction of broiler growth to alleviate problems with the circulatory and skeletal systems and associated mortality (Classen and Riddell, 1989; Classen et al, 1991; Renden et al, 1991) by means of light programs would

TABLE 1. Plasma concentration of corticosterone in male broilers

Age

Time after lights on1 (h) 0 4 20 0 4 20 0 4 20

(d) 13 41 55 ab

Light treatment2 E

I

BI

BE

SEM

S

.294 .343 .372 .152 .138 .171 .156 .246 .166

2.11'

(ng/BnT 1 1.69 1.67 1.76 .50 .75 .50 .52 .52 .46

2.53 2.46 2.30 .71 1.01 .71 .43 .65 .35

1.82 2.72 2.04 .72 .78 .72 .68 .29 .58

2.38 2.24 2.52 .66 .68 .66 .76 1.06 .55

.65" .60"

' Means (SEM = .111) within a column with no common superscript differ significantly (P £ .05). Lights on at 1200 h, and this was operationally defined as 0 h. ^Treatment E = 23 h light (L):l h dark (D) from 1 to 56 d; I = 3L:1D repeated from 1 to 56 d; BI = 6L:18D from 1 to 14 d and Treatment I thereafter to 56 d; BE = 6L:18D from 1 to 14 d and Treatment E thereafter to 56 d of age. 1

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RENDEN ET AL.

seem preferable to feed restriction with regard to the welfare of the chicks. Data for plasma T3 and T4 are shown in Tables 2 and 3, respectively, and were similar to those reported by Dainat et al. (1991). At 13 d of age, there was a significant (P £ .01) light treatment by time of sampling interaction for T3 (Table 2). Chicks in Treatments BI and BE had higher T3 concentrations than chicks in Treatments E and I at the initiation of the light period (0 h), and plasma T3 declined in Treatments BI and BE during time after lights-on. At 13 d of age, both Treatments BI and BE were receiving 6 h of light; blood samples collected at 4 h would have been after 4 h light, and samples collected at 20 h would have been after 14 h of dark. The 4- and 20-h samples for Treatment E would have been after 4 and 20 h of light, respectively. The 4- and 20-h samples for Treatment I would have been at lights-on for both times. At 41 and 55 d of age, Light Treatments E and BE were identical as were Treatments I and BI, and no significant differences in plasma T3 among treatments were found. There was an age by light treatment interaction (P £ .01) for plasma T3 with concentration of T3 lower at 41 and 55 d than at 13 d for all light

treatments and T3 concentration lower at 55 d than 41 d for Treatment I. There was also a light treatment by sampling time interaction (P £ .01) at 13 d of age for plasma T4 concentration (Table 3). An inverse relationship of T4 to T3 among treatments occurred. At time 0 h, chicks in Treatments BI and BE had lower plasma T4 than Treatments E and I, although only Treatments BI and I were significantly (P £ .05) different. A similar pattern occurred at time 4 h, although both Treatments BI and BE had lower plasma T4 than Treatment E. Plasma T4 in Treatments BI and BE was increased at Time 20 h compared with Times 0 and 4 h, and no difference in samples over time were seen in Treatments E and I. As for plasma T3, no differences among treatments occurred at 41 and 55 d, and plasma T4 was elevated at 41 d compared with 13 d. Plasma T3 concentration increases during the light period and decreases during darkness (14 to 16 h light/d), and T4 shows the opposite responses (Newcomer, 1974; Klandorf et al, 1978; Kuhn et al, 1982). However, May (1978) and Smoak and Birrenkott (1986) reported lack of diurnal variation for T3 and T4 for chicks

TABLE 2. Plasma concentration of triiodothyronine in male broilers

Age (d) 13 41 55

Light treatment2

Time after lights on1

E

I

BI

(h) 0 4 20 0 4 20 0 4 20

2.39b,m 2.84 2.72 1.13" 1.20 1.32 1.10" 1.13 1.27

2.30b'm 2.68 2.53 1.78" 1.67 1.43 1.20° 1.11 1.06

3,Ha,m,x 2.68*y 2.17/ 1.32" 1.60 1.67 1.56" 1.23 1.16

BE 3.40,'m'x 2.67Y 2.04X 1.26" 1.38 1.38 1.12" 1.16 1.18

SEM

#

.149 .215 .212 .170 .148 .164 .145 .171 .092

2.80"" 1.37" 1.24"

"-''Means within rows with no common superscript differ significantly (P £ .05). •"-"Means within columns with no common superscript differ significantly (P £ .05). x
CORTTCOSTERONE AND THYROID HORMONES

191

TABLE 3. Plasma concentration of thyroxine in male broilers

Age (d) 13 41 55

Light treatment2

Time after lights on1

E

I

BI

(h) 0 4 20 0 4 20 0 4 20

5.40»b 5.35» 5.31 7.91 4.55 5.45 6.31 4.24 5.55

5.80" 4.19»b 4.62 7.03 6.49 6.84 4.76 5.87 5.90

2.93b'y 2.52"-y 5.38* 4.49 6.77 6.39 5.18 7.08 6.28

BE

SEM

5P

3.80>b'y 3.16"-y 7.01" 6.29 6.56 4.94 5.72 5.92 4.84

.790 .424 .790 1.219 1.045 1.232 .946 .845 .542

4.48y

In

6.43" 5.49*y

•^Means within rows with no common superscript differ significantly (P £ .05). *-yMeans within columns with no common superscript differ significantly (P S .05). lights on at 1200 h, and this was operationally defined as 0 h. ^Treatment E = 23 h light (L):l h dark (D) from 1 to 56 d; I = 3L:1D repeated from 1 to 56 d; BI = 6L:18D from 1 to 14 d and Treatment I thereafter to 56 d; BE = 6L:18D from 1 to 14 d and Treatment E thereafter to 56 d of age. 3 The SEM for age effect = .507 ng/mL.

provided continuous or 23 h of light. Increase in plasma T3 (decrease in T4) is primarily associated with feed intake (May and Reece, 1986) and subsequent increased hepatic conversion of T4 to T3 (Cogburn and Freeman, 1987; Decuypere and Kuhn, 1988; May, 1989). Lighting regimens are known to influence feeding behavior (Cherry and Barwick, 1962; Weaver and Siegel, 1968), and feed consumption of broilers provided 6L:18D was depressed compared with birds provided 23L:1D (Renden et al, 1991). Feed deprivation generally results in decreased plasma T3 and increased T4 (May, 1978; May and Reece, 1986; Cogburn and Freeman, 1987; Decuypere and Kuhn, 1988; Klandorf et al, 1988; May, 1989). The high concentration of plasma T3 at time 0 h for the 13-d-old BI and BE light treatments compared with the E and I treatments was unexpected (Table 2), considering that those broilers were exposed to 18 h of darkness prior to onset of light and that plasma T3 generally decreases during darkness (Newcomer, 1974; Klandorf et al, 1978; Kuhn et al, 1982). However, this discrepancy may be explained by the fact that chicks can learn to consume feed during darkness (Cherry and Barwick, 1962; Squibb and Collier,

1979), although there is a preference for consumption during the light phase (May and Reece, 1986). Feed consumption during darkness was not measured in the present study. Plasma T4 concentrations were lower for the BI and BE treatments at 0 and 4 h compared with E and I (BI significantly lower than I at 0 h, and BI and BE lower than E at 4 h) (Table 3), which would be associated with the deiodination of T4 to T3 (Kuhn et al, 1982). Plasma T4 was increased during the dark period (20 h) for the BI and BE treatments at 13 d of age, which would be expected. Changes in thyroid hormone concentrations over time in Treatments BE and BI at 13 d of age were most likely associated with feeding patterns, particularly with anticipation of lights on (Siegel and Guhl, 1956). Thyroid secretion rate decreases with age (Hendrich and Turner, 1966; Carr and Chiasson, 1983). Triiodothyronine concentration peaks at 1 to 2 wk and decreases with age, and plasma or serum T4 increases after 1 to 2 wk of age (Kuhn et al, 1982; May and Marks, 1983; Stewart and Washburn, 1983; Decuypere and Kuhn, 1988; Goddard et al, 1988). These reports agree with the changes in T3 and T4 with age in the present study.

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King and May (1984) stated that there was not a clear correlation between thyroid hormone concentrations and growth rate of normal chickens; however, McNabb et al. (1989) and McGuinness and Cogburn (1990) indicated that relative growth was positively related to mean daily plasma T3 concentrations. These latter authors did not state the time of blood collection in relation to the photoperiod. In the present study, there were neither significant correlations between relative growth (percentage BW gain) and plasma T3 within light treatments and sampling times at 13 d of age nor across treatments and sampling times within either 41 or 55 d of age (data not shown). Data from the present study indicate that the light schedules did not cause severe stress. Variations in growth rates caused by these light treatments (Renden et al, 1991) were most likely due to the influence of light on feed consumption. Although the data do not seem to indicate that the effect of light treatments on growth was mediated by the endocrine system, variation in plasma hormone binding protein as well as tissue plasma receptor numbers and affinities could influence metabolism without changes in plasma hormone concentrations. Changes in thyroxine-binding prealbumin observed to occur in response to day length alteration have been hypothesized to have a key role in modulating free thyroxine concentrations (El-Sayed et al, 1980). However, results of the present study do not indicate that improvements in leg soundness by use of restricted light programs are associated with alterations in corticosterone or thyroid hormone concentrations. REFERENCES Buckland, R. B., 1975. The effect of intermittent lighting programmes on the production of market chickens and turkeys. World's Poult. Sci. J. 31:262-270. Buckland, R. B., D. E. Bemon, and A. Goldrosen, 1976. Effect of four lighting regimes on broiler performance, leg abnormalities and plasma corticoid levels. Poultry Sci. 55:1072-1076. Burke, W. H., K. D. Arbtan, and N. Snapir, 1990. The role of plasma thyroid hormones in the regulation of body weight of Single Comb White Leghorn and broiler embryos. Poultry Sci. 69: 1388-1393.

Carr, B. L., and R. B. Chiasson, 1983. Age-related changes in pituitary/thyroid function in chickens. Gen. Comp. Endocrinol. 50:18-23. Cherry, P., and M. W. Barwick, 1962. The effect of light on broiler growth. fl\ Light patterns. Br. Poult. Sci. 3:41-49. Classen, H. L., and C. Riddell, 1989. Photoperiodic effects on performance and leg abnormalities in broiler chickens. Poultry Sci. 68:873-879. Classen, H. L., C. Riddell, and F. E. Robinson, 1991. Effects of increasing photoperiod length on performance and health of broiler chickens. Br. Poult. Sci. 32:21-29. Cogburn, L. A., and R. M. Freeman, 1987. Response surface of daily thyroid hormone rhythms in young chickens exposed to constant ambient temperature. Gen. Comp. Endocrinol. 68: 113-123. Dainat, J., L. Saleh, C. Bressot, L. Marger, F. Bacou, and P. Vigneron, 1991. Effects of thyroid state alterations in ovo on the plasma levels of thyroid hormones and on the populations of fibers in the plantaris muscle of male and female chickens. Reprod. Nutr. Dev. 31:703-716. Decuypere, E., and E. R. Kuhn, 1988. Thyroid hormone physiology in galliformes: Age and strain related changes in physiological control. Am. Zool. 28:401-415. El-Sayed, M., D. J. Heaf, and J. Glover, 1980. Effect of changing photoperiod on plasma thyroxinebinding prealbumin in Japanese quail {Coturnix coturnix japonica). Gen. Comp. Endocrinol. 41: 539-545. Freeman, B. M., and I. H. Flack, 1980. Effects of handling on plasma corticosterone concentrations in the immature domestic fowl. Comp. Biochem. Physiol. 66A:77-81. Freeman, B. M., A.C.C. Manning, and I. H. Flack, 1980. Short-term stressor effects of food withdrawal on the immature fowl. Comp. Biochem. Physiol. 67A:569-571. Freeman, B. M., A.C.C. Manning, and I. H. Flack, 1981a. Photoperiod and its effect on the responses of the immature fowl to stressors. Comp. Biochem. Physiol. 68A:411-416. Freeman, B. M., A.C.C. Manning, and I. H. Flack, 1981b. The effects of restricted feeding on adrenal cortical activity in the immature domestic fowl. Br. Poult. Sci. 22:295-303. Gill, J. L., 1981. Repeated measurement and split plot designs. Pages 169-243 in: Design and Analysis of Experiments in the Animal and Medical Sciences. Vol. 2. The Iowa State University Press. Ames, IA. Goddard, C, R. S. Wilkie, and I. C. Dunn, 1988. The relationship between insulin-like growth factor1, growth hormone, thyroid hormones and insulin in chickens selected for growth. Domest. Arum. Endocrinol. 5:165-176. Hendrich, C. E., and C. W. Turner, 1966. Effects of radiothyroidectomy and various replacement levels of thyroxine on growth, organ and gland weights of Cornish Cross chickens. Gen. Comp. Endocrinol. 7:411-419. King, D. B., and J. D. May, 1984. Thyroidal influence on body growth. J. Exp. Zool. 232:453-460. Klandorf, H., G. N. Chua Teco, and I. J. Chopra, 1988. Effect of fatty acid administration on plasma

CORTICOSTERONE AND THYROID HORMONES thyroid hormones in the domestic fowl. Gen. Comp. Endocrinol. 70:395-400. Klandorf, H., P. J. Sharp, and I.J.H. Duncan, 1978. Variations in levels of plasma thyroxine and triiodothyronine in juvenile female chickens during 24- and 16-hr lighting cycles. Gen. Comp. Endocrinol. 36:238-243. Kuhn, E. R., E. Decuypere, L. M. Colen, and H. Michels, 1982. Posthatch growth and development of a circadian rhythm for thyroid hormones in chicks incubated at different temperatures. Poultry Sci. 61:540-549. Lien, R. J., 1988. Involvement of Thyroid Hormones and Prolactin in Events of the Domestic Turkey's Reproductive Cycle. Ph.D. Dissertation, North Carolina State University, Raleigh, NC. May, J. D, 1978. Effect of fasting on T3 and T4 concentrations in chicken serum. Gen. Comp. Endocrinol. 34:323-327. May, J. D., 1989. The role of the thyroid in avian species. Crit. Rev. Poult. Biol. 2:171-186. May, J. D., and H. L. Marks, 1983. Thyroid activity of selected, nonselected, and dwarf broiler lines. Poultry Sci. 62:1721-1724. May, J. D., and F. N. Reece, 1986. Relationship of photoperiod and feed intake to thyroid hormone concentration. Poultry Sci. 65:801-806. McGuinness, M. C, and L. A. Cogburn, 1990. Measurement of developmental changes in plasma insulin-like growth factor-I levels of broiler chickens by radioreceptor assay and radioimmunoassay. Gen. Comp. Endocrinol. 79: 446-458. McNabb, F.M.A., E. A. Dunnington, T. B. Freeman, and P. B. Siegel, 1989. Thyroid hormones and growth patterns of embryonic and posthatch chickens from lines selected for high and low juvenile body weight. Growth Dev. Aging 53: 87-92. Mench, J. A., 1991. Research note: Feed restriction in broiler breeders causes a persistent elevation in corticosterone secretion that is modulated by dietary tryptophan. Poultry Sci. 70:2547-2550. Morris, T. R., 1967. Light requirements of the fowl. Pages 15-39 in: Environmental Control in Poultry Production. T. C. Carter ed., Oliver and Boyd, Ltd. London, England. National Research Council, 1984. Nutrient Requirements of Poultry. 8th rev. ed. National Academy Press, Washington, DC. Newcomer, W. S., 1974. Diurnal rhythms of thyroid function in chicks. Gen. Comp. Endocrinol. 24: 65-73.

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Renden, J. A., S. F. Bilgili, R. J. Lien, and S. A. Kincaid, 1991. Live performance and yields of broilers provided various lighting schedules. Poultry Sci. 70:2055-2062. SAS Institute, 1988. SAS/STAT® User's Guide. Release 6.03 Edition. SAS Institute Inc., Cary, NC. Scott, T. R., D. G. Satterlee, and L. A. Jocobs-Perry, 1983. Circulating corticosterone responses of feed and water deprived broilers and Japanese quail. Poultry Sci. 62:290-297. Siegel, H. S., B. W. Mitchell, N. R. Gould, J. W. Latimer, and R. L. Wilson, 1976. Circadian rhythms for corticosterone, corticosteroid binding capacity, plasma glucose, heart rate, respiration rate, and body temperature in White Rock males. Pages 1050-1061 in: Proceedings of the Fifth European Poultry Congress, Malta. Siegel, P. B., and A. M. Guhl, 1956. The measurement of some rhythms in the activity of White Leghorn cockerels. Poultry Sci. 35:1340-1345. Smoak, K. D., and G. P. Birrenkott, 1986. Daily variation of corticosterone and thyroid hormones in broiler cockerels. Poultry Sci. 65: 197-198. Snedecor, J. G., and W. J. Mellen, 1965. Thyroid deprivation and replacement in chickens. Poultry Sci. 44:452-459. Squibb, R. L., and G. H. Collier, 1979. Feeding behavior of chicks under three lighting regimens. Poultry Sci. 58:641-645. Stewart, P. A., and K. W. Washburn, 1983. Variation in growth hormone, triiodothyronine (T3) and lipogenic enzyme activity in broiler strains differing in growth and fatness. Growth 47: 411-425. Weaver, W. D., Jr., and P. B. Siegel, 1968. Photoperiodism as a factor in feeding rhythms of broiler chickens. Poultry Sci. 47:1148-1154. Williamson, R. A., and T. F. Davison, 1987. Effect of increased circulating corticosterone on serum and thyroidal concentrations of iodothyronines and the responses to thyrotrophin in the immature fowl (Gallus domesticus). Gen. Comp. Endocrinol. 65:65-72. Wodzicka-Tomaszewska, M., T. Stelmasiak, and R. B. Cumming, 1982. Stress by immobilization, with food and water deprivation, causes changes in plasma concentration of triiodothyronine, thyroxine and corticosterone in poultry. Aust. J. Biol. Sci. 35:393-401.