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Effect of Thiouracil on Response to Heat Stress of White Leghorn Lines Selected for Fast and Slow Gain in Two Temperatures1
Effect of Thiouracil on Response to Heat Stress of White Leghorn Lines Selected for Fast and Slow Gain in Two Temperatures1 B. B. BOHREN, J. C. ROGLER, and J. R. CARSON Department of Animal Sciences, Purdue University, West Lafayette, Indiana 47907 (Received for publication May 20, 1981) ABSTRACT Four lines of White Leghorns previously selected for fast and slow gain from 5 to 9 weeks of age in a hot (32.2 C) and in a cold (21.1 C) selection environment were grown from 5 to 9 weeks in the same two temperature environments. Samples of 32 females from each line of the third generation grown in each temperature environment from 5 to 9 weeks of age were divided into two groups; one received .2% thiouracil in the diet for a 5-day period and the other did not. The temperature was then increased to 40.6 C until 52.8% of all birds had died. The percentages of mortality of lines, rearing environments, and thiouracil treatments were then analyzed. An increase of 64.8% mortality from acute heat stress for birds reared in the cold environment was significant, but the differences among the four selected lines were not. The presence of thiouracil in the diet significantly reduced mortality from heat stress by 16.4%. There were no significant interactions between thiouracil treatments and selected lines or rearing environments. (Key words: thiouracil, heat stress, selection, growth rate, poultry) 1983 Poultry Science 62:1104-1106 INTRODUCTION
Marks and Huston (1973) observed that growing quail to 4 weeks of age with .2% thiouracil added to the diet significantly reduced mortality from heat stress at 44.4 C compared to those receiving no thiouracil. Fox (1980), studying adult chickens, found that . 1 % thiouracil in the diet for 4 weeks preceding heat shock resulted in a significant increase in survigal time. Bohren et al. (1981) selected two replicates for four generations in White Leghorns for fast and slow gain in body weight, respectively, from 5 to 9 weeks of age in a hot (32.2 C) and in a normal (21.1 C) environment (hereafter referred to as the cold environment) and tested the four selected lines from each replicate in both temperature environments each generation. After the four lines were reared in the two temperatures from 5 to 9 weeks of age, Bohren et al. (1982) subjected samples from each line reared in each environment to heat stress at 40.6 C with 50% humidity and compared the percentages of mortality when approximately 50% of all birds had died. It was consistently found that the birds reared in the cold environment had significantly more mortality due to the heat stress. Lines selected for fast gain had
'Journal Paper No. 8533, Purdue University Agricultural Experiment Station. This investigation was supported by NIH grant ES00310.
significantly higher mortality than those selected for slow gain in selected Replicate 1 but not in Replicate 2. No differences in mortality were found between the environments in which selection occurred. The purpose of this investigation was to determine if feeding thiouracil would have a differential effect on 1) the lines selected by Bohren et al. (1981) for fast and slow growth, on 2) lines selected in the hot and cold environments, and on 3) birds reared in the hot and cold environments. MATERIALS AND METHODS
This experiment was conducted on females of the third generation of Replicate 2 selected for fast and slow gain, respectively, in a hot (32.2 C) and in a cold (21.1 C) environment reported by Bohren et al. (1981). At 9 weeks of age, one female from each selected line reared from 5 to 9 weeks of age in the hot chamber at 32.2 C was randomly placed in each of 32 growing battery pens in the hot chamber. Similarly, one female from each line reared from 5 to 9 weeks of age in the cold chamber at 21.1 C was placed at random in each of 32 growing battery pens in the cold chamber. Half of the 32 pens in each chamber were fed the same commercial starter ration as previously, and the other half had .2% thiouracil added to the ration. These diets were continued throughout the subsequent heat stress period.
1104
RESEARCH NOTE
1105
TABLE 1. Percent mortality by selected lines and thiouracil treatment after 21 hr of high tempetarure stress (40.6 C) Selected lines and environments
Treatment
Hot
Cold
Hot
Cold
Hot
Cold
Hot
Cold
Means for lines Hot Cold means
Thiouracil No thiouracil
31.2 31.2
68.8 98.4
12.5 25.0
87.5 93.8
6.2 25.0
75.0 98.4
6.2 25.0
68.8 87.5
14.1 26.6
75.0 95.3
Means over treatments
31.2
83.6
18.8
90.6
15.6
86.7
15.6
78.2
20.4
85.2
Hot-fast
Means for lines
57.4
Hot-slow
Cold-fast
51.2
54.7
Three days after birds were 9 weeks of age, the temperature in the hot chamber was elevated to 37.8 C for 48 hr and the cold chamber remained at 21.1 C in order to increase the difference in acclimation effects of the two 5to 9-week rearing environments. After 5 days on the thiouracil treatments, birds from the 32 pens in the cold chamber were combined at random with the 32 pens in the hot chamber having the same thiouracil treatment. Thus; each pen contained 8 pullets, one from each line grown in each temperature environment and on the same thiouracil treatment. The temperature was then increased to 40.6 C and continued for 21 hr, when 52.8% of all birds were dead and the percent mortality of each group was calculated. Percentages were transformed to angles corresponding to the arcsin vproportion after adjustment of all zero values to Vm and all 100% values to l'4n as shown by Steel and Torrie (1980). Analysis of variance was then applied to the transformed
Cold-slow
46.9
44.6 61,0
52.8
values according to the fixed model Y
ijkn = M + L; + Ej + LEjj n- T k + LT i k + ETj k + LETij k + e ( i j k ) n
where /i represents the population mean, L; is the effect of the ith line (i = 1, . . . , 4), E: is the effect of the j m rearing environment (j = 1,2), T k is the effect of the k m thiouracil treatment (k = 1,2), and e/;: k \ n is the random variation among individuals of the same selected line, rearing environment, and thiouracil treatment, which was estimated as the theoretical value of the transformed binomial error or 821/16, where n = 16 is the number of observations in each of the selected line, rearing environment, thiouracil treatment groups (Steel and Torrie, 1980).
RESULTS AND DISCUSSION
The percent mortalities resulting from heat stress at 40.6 C for the selected lines, rearing
TABLE 2. Analysis of variance of the percent mortality (transformed to angles in degrees) from temperature stress for 21 hrs at 40.6 C by selected lines, rearing environment, and thiouracil treatment Source Between selected lines (L) Between rearing environments (E) LX E Between thiouracil treatments (T) T XL T XE TXE.XL Error (821/16) Total
df
3 1 3 1 3 1 3 15
Significant (P<.01).
Mean squares 82.30 8,046.10** 40.28 960.38**
38.65 115.78 76.05 51.31
1106
BOHREN ET AL.
environments, and thiouracil treatments are shown in Table 1. The analysis of variance of the transformed percentages is presented in Table 2. The difference of 64.8% mortality between rearing environments is significant, whereas the differences among the four selected lines were not. This agrees with previous results of Bohren et al. (1982) for this replicate. The presence of .2% thiouracil in the diet significantly reduced the mortality from heat stress in all lines and in both rearing environments by an average of 16.4%. This result agrees with those of Marks and Huston (1973) and Fox (1980) who demonstrated a protective effect of thiouracil against heat stress. None of the interactions were significant, indicating that the effect of thiouracil was consistent for lines selected for fast or slow gain, for lines selected
in the hot or the cold environment, and for both environments in which the birds were reared from 5 to 9 weeks of age. REFERENCES Bohren, B. B., J. R. Carson, and J. C. Rogler, 1981. Response to selection in two temperatures for fast and slow growth to nine weeks of age. Genetics 97:443-450. Bohren, B. B., J. C. Rogler, and J. R. Carson, 1982. Survival under heat stress of lines selected for fast and slow growth at two temperatures. Poultry Sci. 61:1804-1808. Fox, T. W., 1980. The effect of thiouracil and thyroxine on resistance to heat shock. Poultry Sci. 59:2391-2396. Marks, H. L., and T. M. Huston, 1973. Response of selected quail lines to heat stress. Poultry Sci. 52:1668-1670. Steel, R.G.D., and J. H. Torrie. Principles and Procedures of Statistics. McGraw-Hill Book Co., Inc., New York. NY.
Marks and Huston (1973) observed that growing quail to 4 weeks of age with .2% thiouracil added to the diet significantly reduced mortality from heat stress at 44.4 C compared to those receiving no thiouracil. Fox (1980), studying adult chickens, found that . 1 % thiouracil in the diet for 4 weeks preceding heat shock resulted in a significant increase in survigal time. Bohren et al. (1981) selected two replicates for four generations in White Leghorns for fast and slow gain in body weight, respectively, from 5 to 9 weeks of age in a hot (32.2 C) and in a normal (21.1 C) environment (hereafter referred to as the cold environment) and tested the four selected lines from each replicate in both temperature environments each generation. After the four lines were reared in the two temperatures from 5 to 9 weeks of age, Bohren et al. (1982) subjected samples from each line reared in each environment to heat stress at 40.6 C with 50% humidity and compared the percentages of mortality when approximately 50% of all birds had died. It was consistently found that the birds reared in the cold environment had significantly more mortality due to the heat stress. Lines selected for fast gain had
'Journal Paper No. 8533, Purdue University Agricultural Experiment Station. This investigation was supported by NIH grant ES00310.
significantly higher mortality than those selected for slow gain in selected Replicate 1 but not in Replicate 2. No differences in mortality were found between the environments in which selection occurred. The purpose of this investigation was to determine if feeding thiouracil would have a differential effect on 1) the lines selected by Bohren et al. (1981) for fast and slow growth, on 2) lines selected in the hot and cold environments, and on 3) birds reared in the hot and cold environments. MATERIALS AND METHODS
This experiment was conducted on females of the third generation of Replicate 2 selected for fast and slow gain, respectively, in a hot (32.2 C) and in a cold (21.1 C) environment reported by Bohren et al. (1981). At 9 weeks of age, one female from each selected line reared from 5 to 9 weeks of age in the hot chamber at 32.2 C was randomly placed in each of 32 growing battery pens in the hot chamber. Similarly, one female from each line reared from 5 to 9 weeks of age in the cold chamber at 21.1 C was placed at random in each of 32 growing battery pens in the cold chamber. Half of the 32 pens in each chamber were fed the same commercial starter ration as previously, and the other half had .2% thiouracil added to the ration. These diets were continued throughout the subsequent heat stress period.
1104
RESEARCH NOTE
1105
TABLE 1. Percent mortality by selected lines and thiouracil treatment after 21 hr of high tempetarure stress (40.6 C) Selected lines and environments
Treatment
Hot
Cold
Hot
Cold
Hot
Cold
Hot
Cold
Means for lines Hot Cold means
Thiouracil No thiouracil
31.2 31.2
68.8 98.4
12.5 25.0
87.5 93.8
6.2 25.0
75.0 98.4
6.2 25.0
68.8 87.5
14.1 26.6
75.0 95.3
Means over treatments
31.2
83.6
18.8
90.6
15.6
86.7
15.6
78.2
20.4
85.2
Hot-fast
Means for lines
57.4
Hot-slow
Cold-fast
51.2
54.7
Three days after birds were 9 weeks of age, the temperature in the hot chamber was elevated to 37.8 C for 48 hr and the cold chamber remained at 21.1 C in order to increase the difference in acclimation effects of the two 5to 9-week rearing environments. After 5 days on the thiouracil treatments, birds from the 32 pens in the cold chamber were combined at random with the 32 pens in the hot chamber having the same thiouracil treatment. Thus; each pen contained 8 pullets, one from each line grown in each temperature environment and on the same thiouracil treatment. The temperature was then increased to 40.6 C and continued for 21 hr, when 52.8% of all birds were dead and the percent mortality of each group was calculated. Percentages were transformed to angles corresponding to the arcsin vproportion after adjustment of all zero values to Vm and all 100% values to l'4n as shown by Steel and Torrie (1980). Analysis of variance was then applied to the transformed
Cold-slow
46.9
44.6 61,0
52.8
values according to the fixed model Y
ijkn = M + L; + Ej + LEjj n- T k + LT i k + ETj k + LETij k + e ( i j k ) n
where /i represents the population mean, L; is the effect of the ith line (i = 1, . . . , 4), E: is the effect of the j m rearing environment (j = 1,2), T k is the effect of the k m thiouracil treatment (k = 1,2), and e/;: k \ n is the random variation among individuals of the same selected line, rearing environment, and thiouracil treatment, which was estimated as the theoretical value of the transformed binomial error or 821/16, where n = 16 is the number of observations in each of the selected line, rearing environment, thiouracil treatment groups (Steel and Torrie, 1980).
RESULTS AND DISCUSSION
The percent mortalities resulting from heat stress at 40.6 C for the selected lines, rearing
TABLE 2. Analysis of variance of the percent mortality (transformed to angles in degrees) from temperature stress for 21 hrs at 40.6 C by selected lines, rearing environment, and thiouracil treatment Source Between selected lines (L) Between rearing environments (E) LX E Between thiouracil treatments (T) T XL T XE TXE.XL Error (821/16) Total
df
3 1 3 1 3 1 3 15
Significant (P<.01).
Mean squares 82.30 8,046.10** 40.28 960.38**
38.65 115.78 76.05 51.31
1106
BOHREN ET AL.
environments, and thiouracil treatments are shown in Table 1. The analysis of variance of the transformed percentages is presented in Table 2. The difference of 64.8% mortality between rearing environments is significant, whereas the differences among the four selected lines were not. This agrees with previous results of Bohren et al. (1982) for this replicate. The presence of .2% thiouracil in the diet significantly reduced the mortality from heat stress in all lines and in both rearing environments by an average of 16.4%. This result agrees with those of Marks and Huston (1973) and Fox (1980) who demonstrated a protective effect of thiouracil against heat stress. None of the interactions were significant, indicating that the effect of thiouracil was consistent for lines selected for fast or slow gain, for lines selected
in the hot or the cold environment, and for both environments in which the birds were reared from 5 to 9 weeks of age. REFERENCES Bohren, B. B., J. R. Carson, and J. C. Rogler, 1981. Response to selection in two temperatures for fast and slow growth to nine weeks of age. Genetics 97:443-450. Bohren, B. B., J. C. Rogler, and J. R. Carson, 1982. Survival under heat stress of lines selected for fast and slow growth at two temperatures. Poultry Sci. 61:1804-1808. Fox, T. W., 1980. The effect of thiouracil and thyroxine on resistance to heat shock. Poultry Sci. 59:2391-2396. Marks, H. L., and T. M. Huston, 1973. Response of selected quail lines to heat stress. Poultry Sci. 52:1668-1670. Steel, R.G.D., and J. H. Torrie. Principles and Procedures of Statistics. McGraw-Hill Book Co., Inc., New York. NY.