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The relationships of body temperature to weight gain, feed consumption, and feed utilization in broilers under heat stress
The Relationships of Body Temperature to Weight Gain, Feed Consumption, and Feed Utilization in Broilers Under Heat Stress1 M. A. COOPER and K. W. WASHBURN2 Department of Poultry Science, The University of Georgia, Athens, Georgia 30602-2772 heat stress, with mean differences ranging from 0.5 to 1.0 C. Feather weight as a percentage of BW was significantly greater in the 21 C environment (6.22%) than the 32 C environment (5.03%). Mortality was not affected by the heat stress environment. Correlations between body temperature and gain, feed consumption, and feed conversion ratio were low and nonsignificant for most periods in the 21 C environment. In the 32 C environment, body temperature was significantly correlated with gain, feed consumption, and feed conversion ratio after 7 d of heat stress, with mean correlations of –0.40 for gain, –0.31 for feed consumption, and 0.24 for feed conversion ratio in Replicate 1 and –0.44 for gain, –0.40 for feed consumption, and 0.43 for feed conversion ratio in Replicate 2.
(Key words: heat stress, feather cover, feed conversion ratio, body temperature, weight gain) 1998 Poultry Science 77:237–242
tal temperatures increase significantly (Donkoh, 1989). Wilson (1948) found that the individual variation in body temperature was greater at higher air temperatures. Berman (1973) found no correlation between a bird’s temperature in the morning and later times in the day and that morning cloacal temperatures were correlated with growth rate in only one group of experimental birds. However, growth rate was correlated significantly with the diurnal fluctuation in cloacal temperature in all groups. The variation in thermoregulatory ability accounted for 31 to 71% of the total variation in growth rate. Washburn et al. (1980) found a negative phenotypic correlation between body size and resistance to heat stress conditions in growing chickens, which would indicate that if heat stress tolerance were to be measured, differences in BW would need to be included in the analysis. Depressed growth rate and decreased feed consumption of birds grown in higher temperature environments have been reported in many studies over a number of years using many genetic groups (Wilson 1948; Suk and Washburn, 1995). Reports on the effect of environmental temperature on efficiency of feed utilization are not as definitive. Several studies (such as Suk and Washburn, 1995) have shown decreased efficiency of feed utilization with increased environmental temperatures; some studies, such as that of Stilborn et al. (1988), reported no
INTRODUCTION Genetic variation in response to heat stress has been shown to exist between breeds (Fox, 1951, 1980) as well as among sire and dam families (KheirEldin and Shaffner, 1954) for mortality rates as well as for the bird’s ability to control increases in body temperature (Lee et al., 1945). After four generations of divergent selection for survival time of White Leghorn lines at 40.6 C, Wilson et al. (1975) reported that survival time of the lines had diverged by 28 min. Wilson and Plaister (1951) observed that day-old White Leghorn chicks had lower mortality than New Hampshires when exposed to 37.7 C. To optimize feed utilization and body weight gains for the growout of broiler chickens on litter, environmental temperature should be near 21 C (Reece and Deaton, 1971). The body temperature of the adult fowl is normally in the range of 41 to 42 C and significant increases in body temperature occur when environmen-
Received for publication April 12, 1997. Accepted for publication September 24, 1997. 1Supported in part by the state and Hatch funds allocated to the Georgia Agricultural Experiment Stations of The University of Georgia. 2To whom correspondence should be addressed: [email protected]. uga.edu
237
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ABSTRACT Commercial broiler males were used to evaluate body temperature response to heat stress and its relationship to gain, feed consumption, and feed conversion ratio. Individual gain, feed consumption, and feed conversion ratio were obtained from 28 to 49 d in a heat stress environment (32 C) and compared to a 21 C environment. Body temperatures were measured at 28, 35, and 42 d, then daily from 43 to 48 d, and correlated with 28 to 49 d gain, feed consumption, and feed conversion ratio. Feather cover was measured at 51 d of age as a percentage of BW. Initial 28-d body temperature was not significantly different between 21 and 32 C. Body temperature was significantly higher in the 32 C environment after 7 d of heat stress and was significantly higher than at 21 C at all points through 21 d of
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MATERIALS AND METHODS Day-old commercial slow-feathering male broilers (Ross × Ross) were placed in floor pens and provided ad libitum access to the University of Georgia broiler starter ration (22.2% protein, 4.5% fat, and 3,067 kcal ME/kg) and water. At 28 d, 216 birds, in each of two replicates over time, were randomly placed in individual cages, which were described in detail by Guill and Washburn (1972), in a 21 or 32 C controlled environment (108 birds per treatment). From 28 to 49 d, the birds were provided ad libitum access to the University of Georgia broiler finisher ration (21% protein, 7.5% fat, and 3,230 kcal ME/kg) and water. Birds were provided continuous lighting through 49 d. At 28 d, individual body and feed weights and basal (before heat stress) cloacal temperatures were obtained. Body temperatures were obtained with a thermocouple thermometer3 inserted approximately 3 cm into the
3Digital
Type E, Cole Palmer Instrument Co., Chicago, IL 60648.
cloaca. The two thermometers used were calibrated before and after obtaining cloacal temperatures on each day samples were obtained. Temperatures were taken during the same 1-h time span on the sampling days so that diurnal fluctuations in body temperature would not affect the results. One-third of the birds were sampled in one temperature environment before sampling the next one-third in the other temperature environment until all birds were sampled. Each day, the beginning environment for sampling was alternated. Body and feed weights were obtained at 35, 42, and 49 d and gain, feed consumption, and feed conversion ratio were calculated. The cloacal temperatures were obtained at 28, 35, 42, 46, 48, and 49 d (Replicate 1) and at 28, 35, 46, 48, and 50 d (Replicate 2). Mortality was recorded daily. The day after obtaining the final temperatures, 50 (Replicate 1) or 51 d (Replicate 2), the birds were euthanatized by CO2 asphyxiation and weighed (Weight before). After scalding and removal of feathers, residual feathers were removed by hand. The carcasses were dried by a combination of blotting with paper towels and forced air for a 10-min period. The birds were then weighed (Weight after). Percentage feather weight (feather cover) was calculated by the following procedure: Weight before – Weight after = Feather weight, (Feather weight/Weight before) × 100 = percentage feather weight. Analysis of variance and correlations between body temperature and the economic traits were conducted using the procedures of SAS (SAS Institute, 1985). Differences between temperatures were analyzed using the General Linear Models (GLM) procedure of SAS along with Duncan’s multiple range test to separate means (Duncan, 1955). All statements of significance are based on a probability level of 0.05.
RESULTS AND DISCUSSION
Production Traits Heat stress temperatures resulted in a significant decrease in gain throughout the experimental period of Replicate 1 and through the 28 to 35 and 35 to 42 d in Replicate 2 (Figure 1). The gain for the final week of Replicate 2 was lower in the heat stress environment; however, the difference was not significant due to the decreased growth of birds in the 21 C room. This decreased growth during the 42- to 49-d period may have been due to the large size of the birds in Replicate 2 at 42 d, resulting in difficulty in obtaining sufficient feed and water to continue the rapid gain in the individual cage system. Over the 28- to 49-d experimental period, heat stress of 32 C resulted in a 35% decrease in gain, which is similar to results of other studies, but higher than results obtained by Vo et al. (1978). Calculations from their data indicated that when birds were reared in temperatures similar to the present study a 20 to 30% decrease in gain was observed. The greater depression in gain would be
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significant effects of heat stress on efficiency of feed utilization, whereas other studies, such as that of Deaton et al. (1968), reported that feed utilization was improved under hot environmental temperatures. Deaton et al. (1972) reported that the effect of heat stress on efficiency of feed utilization varied with age. Deaton et al. (1968) and Donkoh (1989), using environmental temperatures similar to those of the present study (up to 32 C), found that environmental temperature did not affect mortality, but a significant increase in mortality was observed by Vo et al. (1977) when the environmental temperature was increased to 37.8 C. A number of studies have been conducted on the effect of differences in feather cover between breeds (including naked neck and featherless populations), on economic traits. Cahaner et al. (1993) using a naked neck line back-crossed to commercial broiler lines, found that decreased feather cover increased BW gains in a normal temperature and reported an increased advantage in high temperature environments of decreased feather cover associated with the naked neck gene. Hancock et al. (1995) estimated that feather weight made up 0.062 and 0.050% of the mature BW of female and male broilers, respectively; however, no differences between the broiler strains used were observed. Brake et al. (1993) found that feather weight as a percentage of BW changed with age from 28 to 49 d. The present experiment studied the effect of environmental temperature on production traits (weight gain, feed consumption, and feed conversion ratio) as well as body temperature and feather cover of a commercial broiler strain. The association of body temperature and feather cover to these production traits as well as the effects of environmental temperature on this association were also studied.
BODY TEMPERATURE AND ECONOMIC TRAITS
239
FIGURE 2. The effect of heat stress on feed conversion ratio (FCR) from 28 to 49 d of age. Rep = replicate. *P < 0.05.
expected due to the larger size of the broilers used in the present study compared to those used by Vo et al. (1978). Heat stress temperatures resulted in a significant increase in feed conversion ratio throughout the experimental period of Replicate 1 and through the first 2 wk of Replicate 2 (Figure 2); however, no significant difference was observed in the 3rd wk of Replicate 2 because of the decreased growth of birds in the 21 C room. For the 28- to 49-d experimental period, the birds in the 21 C environment required 2.05 g feed to obtain a 1-g increase in BW as compared to 2.37 g of feed needed by the birds in the 32 C environment. Heat stress resulted in similar increases in feed conversion ratio in the studies of Bottje and Harrison (1985) and Suk and Washburn (1995). The mean weekly feed conversion ratio in both environments increased throughout the experimental period of both replicates with one exception caused by an unusually high 28 to 35 d feed conversion ratio in the 32 C environment of Replicate 2. The trend of increasing feed conversion ratio with age was observed as decreasing efficiency of feed utilization by Barrot and Pringle (1950). Heat stress of 32 C throughout the experimental period did not affect mortality. Mortality was very low in all groups (one dead in 21 C environment and two dead in the 32 C
environment in Replicate 1 and no deaths in Replicate 2). Similar results were obtained for similar temperatures by Deaton et al. (1968) and Vo et al. (1977, 1978).
Feather Cover Feather cover was significantly reduced in the 32 C environment in both replicates, 6.22 vs 5.03% in Replicate 1, and 6.93 vs 6.32% in Replicate 2. Feather cover was not significantly correlated with any of the economic traits (BW, gain, feed consumption, or feed conversion ratio) nor was feather cover correlated with body temperature at any age in the normal environment (21 C) of Replicate 1 or in either environment of Replicate 2. These non-significant correlations are not presented. Feather cover was significantly correlated with 49-d BW (0.42), overall gain (0.39), and overall feed conversion ratio (–0.47) in the 32 C environment of Replicate 1. These correlations between feather cover, in the 32 C environment of Replicate 1, and the economic traits were similar to those seen in the study by Cahaner et al. (1993). Using a naked neck line backcrossed to commercial broiler sire lines, they found that decreased feather cover was associated with increased body weight gains in normal temperatures, with
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FIGURE 1. The effect of heat stress on weight gain from 28 to 49 d of age. Rep = replicate. *P < 0.05.
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COOPER AND WASHBURN TABLE 1. Correlation between body temperature at different ages and body weight gain (Gain), feed consumption (Cons), and feed conversion ratio (FCR) at 21 and 32 C for Replicate 1 28 d
Variable
42 d
46 d
48 d
49 d
32 C
21 C
32 C
21 C
32 C
21 C
32 C
21 C
32 C
21 C
32 C
35 42 49 49
d d d d
0.06 –0.10 –0.13 –0.07
–0.16 –0.10 –0.07 –0.14
0.08 0.02 0.03 0.07
–0.24* –0.58* –0.48* –0.55*
–0.17 0.02 0.07 –0.06
–0.21* –0.47* –0.51* –0.51*
0.14 0.06 0.05 0.13
–0.28* –0.49* –0.48* –0.53*
–0.02 0.01 0.18 0.07
–0.26* –0.34* –0.37* –0.41*
–0.03 0.15 0.24* 0.17
–0.09 –0.20* –0.04 –0.13
35 42 49 49
d d d d
0.18 –0.05 –0.07 0.02
–0.16 –0.12 –0.17 –0.18
0.12 0.07 0.01 0.08
0.16 –0.42* –0.38* –0.38*
–0.20 0.00 0.01 –0.08
–0.20* –0.32* –0.32* –0.34*
0.13 0.12 0.08 0.14
–0.11 –0.35* –0.43* –0.37*
0.00 0.00 0.18 0.08
–0.14 –0.28* –0.27* –0.28*
–0.02 0.12 0.26* 0.17
–0.17 –0.20* –0.13 –0.20*
35 42 49 49
d d d d
0.15 0.07 0.08 0.15
0.08 0.06 –0.05 0.06
–0.01 0.05 –0.03 0.00
0.19 0.45* 0.23* 0.44*
0.07 –0.02 –0.09 –0.04
0.09 0.37* 0.37* 0.44*
–0.16 0.11 0.03 0.03
0.30* 0.39* 0.23* 0.42*
0.07 –0.01 –0.02 0.03
0.22* 0.22* 0.15 0.29*
0.05 –0.03 –0.02 0.02
–0.05 0.12 –0.18 –0.06
*P < 0.05.
increasing benefit as environmental temperatures increased. Although we did not observe differences within the 21 C environment due to feather cover, variation among individual feather cover in this study would not be expected to have been as dramatic as those observed by Cahaner et al. (1993) due to their use of the naked neck gene population.
however, the correlations between body temperature and the economic traits for the remaining ages became larger and highly significant in both replicates.
Body Temperature Heat stress temperature (32 C) resulted in a significant increase in body temperature in both replicates throughout the experimental period (Figure 3). This relationship between high environmental temperature and increased body temperature agrees with conclusions in many other studies using genetic strains quite different from the broilers used in this study. Correlations between body temperature and the economic traits of gain, feed consumption, and feed conversion ratio were dependent upon the time in experimental conditions, which cannot be separated from age. In Replicate 1, the correlations between body temperature at 28 d and the data on economic traits obtained during the experimental period were generally low and nonsignificant at all ages and for both normal and heat stress environments in both Replicates 1 and 2 (Tables 1 and 2). There was a clear-cut change in the correlations of body temperature after 28 d with gain, feed consumption, and feed conversion ratio in both replicates. In the 21 C environment, the correlations were generally low and were significant in only 2 of 60 correlations (0.24 and 0.26) for Replicate 1. Similar results were observed in Replicate 2 with significance in only 5 of 48 correlations (0.28, 0.28, 0.33, 0.33, and 0.34) over the 28 to 49 d experimental period. In the 32 C environment, the same trend of low (but negative) correlations between body temperature and the economic traits were evident for the early ages (28 to 35 d gain, feed consumption, and feed conversion ratio);
FIGURE 3. The effect of heat stress on body temperature from 28 to 49 d of age. Rep = replicate. Significant differences (P < 0.05) were observed at all days measured except the 28th d of Rep 1.
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Gain 28 to 35 to 42 to 28 to Cons 28 to 35 to 42 to 28 to FCR 28 to 35 to 42 to 28 to
35 d
21 C
241
BODY TEMPERATURE AND ECONOMIC TRAITS TABLE 2. Correlation between body temperature at different ages and body weight gain (Gain), feed consumption (Cons), and feed conversion ratio (FCR) at 2 and 32 C for Replicate 2 28 d Variable
46 d
48 d
32 C
21 C
32 C
21 C
32 C
21 C
50 d 32 C
21 C
32 C
35 42 49 49
d d d d
0.07 –0.02 0.42* 0.31*
0.05 –0.18 –0.21 –0.19
0.26 0.20 0.17 0.34*
–0.44* –0.53* –0.59* –0.60*
–0.04 0.05 0.22 0.16
–0.52* –0.56* –0.34* –0.60*
0.11 0.28* 0.20 0.33*
–0.48* –0.54* –0.36* –0.59*
0.09 0.21 0.05 0.18
–0.49* –0.42* –0.20 –0.47*
35 42 49 49
d d d d
0.27 –0.09 0.32* 0.19
0.15 –0.05 –0.22 –0.13
0.25 0.16 0.12 0.28*
–0.19 –0.37* –0.50* –0.45*
0.06 0.01 0.04 0.05
–0.43* –0.57* –0.19 –0.54*
0.10 0.26 0.07 0.27
–0.26 –0.52* –0.39* –0.55*
0.19 0.24 0.14 0.33*
–0.27* –0.44* –0.18 –0.41*
35 42 49 49
d d d d
0.28* –0.08 –0.28* –0.17
0.06 0.20 –0.05 0.22
0.47* 0.50* 0.20 0.59*
0.16 –0.04 –0.19 –0.14
0.43* 0.40* 0.08 0.57*
–0.06 0.03 –0.13 –0.15
0.53* 0.47* –0.06 0.55*
–0.15 –0.01 –0.20 –0.16
0.08 0.08 –0.08 0.13
0.51* 0.33* –0.22 0.46*
*P < 0.05.
In Replicate 1, the mean correlation between body temperature (at 35, 42, 46, 48, and 49 d) and the 35 to 42 and 42 to 49 d gain was –0.40 and the median was –0.48 for the 32 C environment as compared to a mean of 0.08 and a median of 0.06 for the same correlations in the 21 C environment. The mean correlation between body temperature and the 35 to 42 and 42 to 49 d feed consumption was –0.31 and the median was –0.32 for the 32 C environment as compared to a mean of 0.09 and a median of 0.08 for the same correlations in the 21 C environment. The mean correlation between body temperature and the 35 to 42 and 42 to 49 d feed conversion ratio was 0.24 and the median was 0.23 for the 32 C environment as compared to a mean of 0.00 and a median of –0.02 for the same correlations in the 21 C environment. In Replicate 2, the correlations between body temperature (at 35, 46, 48, and 50 d) and gain, feed consumption, and feed conversion ratio were similar to those of Replicate 1 with the exception of the 42 to 49 d feed conversion ratio, which is probably due to the decreased growth of the birds in Replicate 2 during the 42 to 49 d period. In Replicate 2, the mean correlation between body temperature and the 35 to 42 and 42 to 49 d gain was –0.44 and the median was –0.48 for the 32 C environment, as compared to a mean of 0.17 and a median of 0.21 for the same correlations in the 21 C environment. The mean correlation between body temperature and the 35 to 42 and 42 to 49 d feed consumption was –0.40 and the median was –0.42 for the 32 C environment as compared to a mean of 0.13 and a median of 0.13 for the same correlations in the 21 C environment. The mean correlation between body temperature and the 35 to 42 d feed conversion ratio was 0.43 and the median was 0.37 for the 32 C environment as compared to a mean of 0.02 and a median of 0.02 for the same correlations in the 21 C environment. The mean correlations between the body temperature and the 42 to 49 d feed conversion ratio was 0.00 and the median was
0.01 for the 32 C environment as compared to a mean of –0.15 and a median of –0.16 for the same correlations in the 21 C environment. These results indicate a lack of association between body temperature and traits of economic importance in broilers in a normal (21 C) environment. However, when exposed to a heat stress environment there is a strong negative correlation between body temperature and traits of economic importance after 1 wk of heat stress exposure.
REFERENCES Barrott, H. G., and E. M. Pringle, 1950. Effect of environment on growth and feed and water consumption of chickens. J. Nutr. 41:25–30. Berman, A., 1973. Homeothermy and growth rate in the fowl. Br. Poult. Sci. 14:319–328. Bottje, W. G., and P. C. Harrison, 1985. Effect of carbonated water on growth performance of cockerels subjected to constant and cyclic heat stress temperatures. Poultry Sci. 64: 1285–1292. Brake, J., G. B. Havenstein, S. E. Scheideler, P. R. Ferket, and D. V. Rives, 1993. Relationship of sex, age, and body weight to broiler carcass yield and offal production. Poultry Sci. 72: 1137–1145. Cahaner, A., N. Deeb, and M. Gutman, 1993. Effects of the plumage-reducing naked neck (Na) gene on performance of fast-growing broilers at normal and high ambient temperatures. Poultry Sci. 72:767–775. Deaton, J. W., F. N. Reece, B. D. Lott, L. F. Kubena, and J. D. May, 1972. The efficiency of cooling broilers in summer as measured by growth and feed utilization. Poultry Sci. 51: 69–71. Deaton, J. W., F. N. Reece, and T. H. Vardaman, 1968. The effect of temperature and density on broiler performance. Poultry Sci. 47:293–300. Donkoh, A., 1989. Ambient temperature: a factor affecting performance and physiological response of broiler chickens. Int. J. Biometeorol. 33:259–265.
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Gain 28 to 35 to 42 to 28 to Cons 28 to 35 to 42 to 28 to FCR 28 to 35 to 42 to 28 to
35 d
21 C
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COOPER AND WASHBURN (aspirin) in the diet of broilers maintained under heat stress conditions. Poultry Sci. 67:1183–1187. Suk, Y. O., and K. W. Washburn, 1995. Effects of environment on growth, efficiency of feed utilization, carcass fatness, and their association. Poultry Sci. 74:285–296. Vo, K. V., M. A. Boone, and W. E. Johnston, 1978. Effect of three lifetime ambient temperatures on growth, feed and water consumption and various blood components in male and female leghorn chickens. Poultry Sci. 57:798–803. Vo, K. V., M. A. Boone, and W. E. Mulliken, 1977. Exposure of broilers to continuous high temperature stress. Poult. Res. Series No. 36, Clemson University, Clemson, SC. Washburn, K. W., R. Peavey, and G. M. Renwick, 1980. Relationship of strain variation and feed restriction to variation in blood pressure response to heat stress. Poultry Sci. 59:2586–2588. Wilson, H. R., C. J. Wilcox, R. A. Voitle, C. D. Baird, and R. W. Dorminey, 1975. Characteristics of white leghorn chickens selected for heat tolerance. Poultry Sci. 54:126–130. Wilson, W. O., 1948. Some effects of increasing environmental temperatures on pullets. Poultry Sci. 27:813–817. Wilson, W. O., and T. H. Plaister, 1951. Breed differences in heat tolerance of day-old baby chicks. Poultry Sci. 30:625–627.
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Duncan, D. B., 1955. Multiple range and multiple F tests. Biometrics 11:1–42. Fox, T. W., 1951. Studies on heat tolerance in the domestic fowl. Poultry Sci. 30:477–483. Fox, T. W., 1980. The effects of thiouracil and thyroxine on resistance to heat shock. Poultry Sci. 59:2391–2396. Guill, R. A., and K. W. Washburn, 1972. Cages and feeders for individual broiler feed consumption experiments. Poultry Sci. 51:1047–1048. Hancock, C. E., G. D. Bradford, G. C. Emmans, and R. M. Gous, 1995. The evaluation of the growth parameters of six strains of commercial broiler chickens. Br. Poult. Sci. 36:247–264. KheirEldin, M. A., and C. S. Shaffner, 1954. Familial differences in resistance to high environmental temperatures in chicks. Poultry Sci. 33:1064. Lee, D.H.K., K. W. Robinson, N.T.M. Yeates, and M.I.R. Scott, 1945. Poultry husbandry in hot climates—experimental inquiries. Poultry Sci. 24:195–207. Reece, F. N., and J. W. Deaton, 1971. Use of a time-proportioning thermostat for control of poultry-house environments. Poultry Sci. 50:1622. SAS Institute, 1985. SAS User’s Guide: Statistics. Version 5 Edition. SAS Institute Inc., Cary, NC. Stilborn, H. L., G. C. Harris, Jr., W. G. Bottje, and P. W. Waldroup, 1988. Ascorbic acid and acetylsalicylic acid
(Key words: heat stress, feather cover, feed conversion ratio, body temperature, weight gain) 1998 Poultry Science 77:237–242
tal temperatures increase significantly (Donkoh, 1989). Wilson (1948) found that the individual variation in body temperature was greater at higher air temperatures. Berman (1973) found no correlation between a bird’s temperature in the morning and later times in the day and that morning cloacal temperatures were correlated with growth rate in only one group of experimental birds. However, growth rate was correlated significantly with the diurnal fluctuation in cloacal temperature in all groups. The variation in thermoregulatory ability accounted for 31 to 71% of the total variation in growth rate. Washburn et al. (1980) found a negative phenotypic correlation between body size and resistance to heat stress conditions in growing chickens, which would indicate that if heat stress tolerance were to be measured, differences in BW would need to be included in the analysis. Depressed growth rate and decreased feed consumption of birds grown in higher temperature environments have been reported in many studies over a number of years using many genetic groups (Wilson 1948; Suk and Washburn, 1995). Reports on the effect of environmental temperature on efficiency of feed utilization are not as definitive. Several studies (such as Suk and Washburn, 1995) have shown decreased efficiency of feed utilization with increased environmental temperatures; some studies, such as that of Stilborn et al. (1988), reported no
INTRODUCTION Genetic variation in response to heat stress has been shown to exist between breeds (Fox, 1951, 1980) as well as among sire and dam families (KheirEldin and Shaffner, 1954) for mortality rates as well as for the bird’s ability to control increases in body temperature (Lee et al., 1945). After four generations of divergent selection for survival time of White Leghorn lines at 40.6 C, Wilson et al. (1975) reported that survival time of the lines had diverged by 28 min. Wilson and Plaister (1951) observed that day-old White Leghorn chicks had lower mortality than New Hampshires when exposed to 37.7 C. To optimize feed utilization and body weight gains for the growout of broiler chickens on litter, environmental temperature should be near 21 C (Reece and Deaton, 1971). The body temperature of the adult fowl is normally in the range of 41 to 42 C and significant increases in body temperature occur when environmen-
Received for publication April 12, 1997. Accepted for publication September 24, 1997. 1Supported in part by the state and Hatch funds allocated to the Georgia Agricultural Experiment Stations of The University of Georgia. 2To whom correspondence should be addressed: [email protected]. uga.edu
237
Downloaded from http://ps.oxfordjournals.org/ at University of Waikato Library on July 7, 2014
ABSTRACT Commercial broiler males were used to evaluate body temperature response to heat stress and its relationship to gain, feed consumption, and feed conversion ratio. Individual gain, feed consumption, and feed conversion ratio were obtained from 28 to 49 d in a heat stress environment (32 C) and compared to a 21 C environment. Body temperatures were measured at 28, 35, and 42 d, then daily from 43 to 48 d, and correlated with 28 to 49 d gain, feed consumption, and feed conversion ratio. Feather cover was measured at 51 d of age as a percentage of BW. Initial 28-d body temperature was not significantly different between 21 and 32 C. Body temperature was significantly higher in the 32 C environment after 7 d of heat stress and was significantly higher than at 21 C at all points through 21 d of
238
COOPER AND WASHBURN
MATERIALS AND METHODS Day-old commercial slow-feathering male broilers (Ross × Ross) were placed in floor pens and provided ad libitum access to the University of Georgia broiler starter ration (22.2% protein, 4.5% fat, and 3,067 kcal ME/kg) and water. At 28 d, 216 birds, in each of two replicates over time, were randomly placed in individual cages, which were described in detail by Guill and Washburn (1972), in a 21 or 32 C controlled environment (108 birds per treatment). From 28 to 49 d, the birds were provided ad libitum access to the University of Georgia broiler finisher ration (21% protein, 7.5% fat, and 3,230 kcal ME/kg) and water. Birds were provided continuous lighting through 49 d. At 28 d, individual body and feed weights and basal (before heat stress) cloacal temperatures were obtained. Body temperatures were obtained with a thermocouple thermometer3 inserted approximately 3 cm into the
3Digital
Type E, Cole Palmer Instrument Co., Chicago, IL 60648.
cloaca. The two thermometers used were calibrated before and after obtaining cloacal temperatures on each day samples were obtained. Temperatures were taken during the same 1-h time span on the sampling days so that diurnal fluctuations in body temperature would not affect the results. One-third of the birds were sampled in one temperature environment before sampling the next one-third in the other temperature environment until all birds were sampled. Each day, the beginning environment for sampling was alternated. Body and feed weights were obtained at 35, 42, and 49 d and gain, feed consumption, and feed conversion ratio were calculated. The cloacal temperatures were obtained at 28, 35, 42, 46, 48, and 49 d (Replicate 1) and at 28, 35, 46, 48, and 50 d (Replicate 2). Mortality was recorded daily. The day after obtaining the final temperatures, 50 (Replicate 1) or 51 d (Replicate 2), the birds were euthanatized by CO2 asphyxiation and weighed (Weight before). After scalding and removal of feathers, residual feathers were removed by hand. The carcasses were dried by a combination of blotting with paper towels and forced air for a 10-min period. The birds were then weighed (Weight after). Percentage feather weight (feather cover) was calculated by the following procedure: Weight before – Weight after = Feather weight, (Feather weight/Weight before) × 100 = percentage feather weight. Analysis of variance and correlations between body temperature and the economic traits were conducted using the procedures of SAS (SAS Institute, 1985). Differences between temperatures were analyzed using the General Linear Models (GLM) procedure of SAS along with Duncan’s multiple range test to separate means (Duncan, 1955). All statements of significance are based on a probability level of 0.05.
RESULTS AND DISCUSSION
Production Traits Heat stress temperatures resulted in a significant decrease in gain throughout the experimental period of Replicate 1 and through the 28 to 35 and 35 to 42 d in Replicate 2 (Figure 1). The gain for the final week of Replicate 2 was lower in the heat stress environment; however, the difference was not significant due to the decreased growth of birds in the 21 C room. This decreased growth during the 42- to 49-d period may have been due to the large size of the birds in Replicate 2 at 42 d, resulting in difficulty in obtaining sufficient feed and water to continue the rapid gain in the individual cage system. Over the 28- to 49-d experimental period, heat stress of 32 C resulted in a 35% decrease in gain, which is similar to results of other studies, but higher than results obtained by Vo et al. (1978). Calculations from their data indicated that when birds were reared in temperatures similar to the present study a 20 to 30% decrease in gain was observed. The greater depression in gain would be
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significant effects of heat stress on efficiency of feed utilization, whereas other studies, such as that of Deaton et al. (1968), reported that feed utilization was improved under hot environmental temperatures. Deaton et al. (1972) reported that the effect of heat stress on efficiency of feed utilization varied with age. Deaton et al. (1968) and Donkoh (1989), using environmental temperatures similar to those of the present study (up to 32 C), found that environmental temperature did not affect mortality, but a significant increase in mortality was observed by Vo et al. (1977) when the environmental temperature was increased to 37.8 C. A number of studies have been conducted on the effect of differences in feather cover between breeds (including naked neck and featherless populations), on economic traits. Cahaner et al. (1993) using a naked neck line back-crossed to commercial broiler lines, found that decreased feather cover increased BW gains in a normal temperature and reported an increased advantage in high temperature environments of decreased feather cover associated with the naked neck gene. Hancock et al. (1995) estimated that feather weight made up 0.062 and 0.050% of the mature BW of female and male broilers, respectively; however, no differences between the broiler strains used were observed. Brake et al. (1993) found that feather weight as a percentage of BW changed with age from 28 to 49 d. The present experiment studied the effect of environmental temperature on production traits (weight gain, feed consumption, and feed conversion ratio) as well as body temperature and feather cover of a commercial broiler strain. The association of body temperature and feather cover to these production traits as well as the effects of environmental temperature on this association were also studied.
BODY TEMPERATURE AND ECONOMIC TRAITS
239
FIGURE 2. The effect of heat stress on feed conversion ratio (FCR) from 28 to 49 d of age. Rep = replicate. *P < 0.05.
expected due to the larger size of the broilers used in the present study compared to those used by Vo et al. (1978). Heat stress temperatures resulted in a significant increase in feed conversion ratio throughout the experimental period of Replicate 1 and through the first 2 wk of Replicate 2 (Figure 2); however, no significant difference was observed in the 3rd wk of Replicate 2 because of the decreased growth of birds in the 21 C room. For the 28- to 49-d experimental period, the birds in the 21 C environment required 2.05 g feed to obtain a 1-g increase in BW as compared to 2.37 g of feed needed by the birds in the 32 C environment. Heat stress resulted in similar increases in feed conversion ratio in the studies of Bottje and Harrison (1985) and Suk and Washburn (1995). The mean weekly feed conversion ratio in both environments increased throughout the experimental period of both replicates with one exception caused by an unusually high 28 to 35 d feed conversion ratio in the 32 C environment of Replicate 2. The trend of increasing feed conversion ratio with age was observed as decreasing efficiency of feed utilization by Barrot and Pringle (1950). Heat stress of 32 C throughout the experimental period did not affect mortality. Mortality was very low in all groups (one dead in 21 C environment and two dead in the 32 C
environment in Replicate 1 and no deaths in Replicate 2). Similar results were obtained for similar temperatures by Deaton et al. (1968) and Vo et al. (1977, 1978).
Feather Cover Feather cover was significantly reduced in the 32 C environment in both replicates, 6.22 vs 5.03% in Replicate 1, and 6.93 vs 6.32% in Replicate 2. Feather cover was not significantly correlated with any of the economic traits (BW, gain, feed consumption, or feed conversion ratio) nor was feather cover correlated with body temperature at any age in the normal environment (21 C) of Replicate 1 or in either environment of Replicate 2. These non-significant correlations are not presented. Feather cover was significantly correlated with 49-d BW (0.42), overall gain (0.39), and overall feed conversion ratio (–0.47) in the 32 C environment of Replicate 1. These correlations between feather cover, in the 32 C environment of Replicate 1, and the economic traits were similar to those seen in the study by Cahaner et al. (1993). Using a naked neck line backcrossed to commercial broiler sire lines, they found that decreased feather cover was associated with increased body weight gains in normal temperatures, with
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FIGURE 1. The effect of heat stress on weight gain from 28 to 49 d of age. Rep = replicate. *P < 0.05.
240
COOPER AND WASHBURN TABLE 1. Correlation between body temperature at different ages and body weight gain (Gain), feed consumption (Cons), and feed conversion ratio (FCR) at 21 and 32 C for Replicate 1 28 d
Variable
42 d
46 d
48 d
49 d
32 C
21 C
32 C
21 C
32 C
21 C
32 C
21 C
32 C
21 C
32 C
35 42 49 49
d d d d
0.06 –0.10 –0.13 –0.07
–0.16 –0.10 –0.07 –0.14
0.08 0.02 0.03 0.07
–0.24* –0.58* –0.48* –0.55*
–0.17 0.02 0.07 –0.06
–0.21* –0.47* –0.51* –0.51*
0.14 0.06 0.05 0.13
–0.28* –0.49* –0.48* –0.53*
–0.02 0.01 0.18 0.07
–0.26* –0.34* –0.37* –0.41*
–0.03 0.15 0.24* 0.17
–0.09 –0.20* –0.04 –0.13
35 42 49 49
d d d d
0.18 –0.05 –0.07 0.02
–0.16 –0.12 –0.17 –0.18
0.12 0.07 0.01 0.08
0.16 –0.42* –0.38* –0.38*
–0.20 0.00 0.01 –0.08
–0.20* –0.32* –0.32* –0.34*
0.13 0.12 0.08 0.14
–0.11 –0.35* –0.43* –0.37*
0.00 0.00 0.18 0.08
–0.14 –0.28* –0.27* –0.28*
–0.02 0.12 0.26* 0.17
–0.17 –0.20* –0.13 –0.20*
35 42 49 49
d d d d
0.15 0.07 0.08 0.15
0.08 0.06 –0.05 0.06
–0.01 0.05 –0.03 0.00
0.19 0.45* 0.23* 0.44*
0.07 –0.02 –0.09 –0.04
0.09 0.37* 0.37* 0.44*
–0.16 0.11 0.03 0.03
0.30* 0.39* 0.23* 0.42*
0.07 –0.01 –0.02 0.03
0.22* 0.22* 0.15 0.29*
0.05 –0.03 –0.02 0.02
–0.05 0.12 –0.18 –0.06
*P < 0.05.
increasing benefit as environmental temperatures increased. Although we did not observe differences within the 21 C environment due to feather cover, variation among individual feather cover in this study would not be expected to have been as dramatic as those observed by Cahaner et al. (1993) due to their use of the naked neck gene population.
however, the correlations between body temperature and the economic traits for the remaining ages became larger and highly significant in both replicates.
Body Temperature Heat stress temperature (32 C) resulted in a significant increase in body temperature in both replicates throughout the experimental period (Figure 3). This relationship between high environmental temperature and increased body temperature agrees with conclusions in many other studies using genetic strains quite different from the broilers used in this study. Correlations between body temperature and the economic traits of gain, feed consumption, and feed conversion ratio were dependent upon the time in experimental conditions, which cannot be separated from age. In Replicate 1, the correlations between body temperature at 28 d and the data on economic traits obtained during the experimental period were generally low and nonsignificant at all ages and for both normal and heat stress environments in both Replicates 1 and 2 (Tables 1 and 2). There was a clear-cut change in the correlations of body temperature after 28 d with gain, feed consumption, and feed conversion ratio in both replicates. In the 21 C environment, the correlations were generally low and were significant in only 2 of 60 correlations (0.24 and 0.26) for Replicate 1. Similar results were observed in Replicate 2 with significance in only 5 of 48 correlations (0.28, 0.28, 0.33, 0.33, and 0.34) over the 28 to 49 d experimental period. In the 32 C environment, the same trend of low (but negative) correlations between body temperature and the economic traits were evident for the early ages (28 to 35 d gain, feed consumption, and feed conversion ratio);
FIGURE 3. The effect of heat stress on body temperature from 28 to 49 d of age. Rep = replicate. Significant differences (P < 0.05) were observed at all days measured except the 28th d of Rep 1.
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Gain 28 to 35 to 42 to 28 to Cons 28 to 35 to 42 to 28 to FCR 28 to 35 to 42 to 28 to
35 d
21 C
241
BODY TEMPERATURE AND ECONOMIC TRAITS TABLE 2. Correlation between body temperature at different ages and body weight gain (Gain), feed consumption (Cons), and feed conversion ratio (FCR) at 2 and 32 C for Replicate 2 28 d Variable
46 d
48 d
32 C
21 C
32 C
21 C
32 C
21 C
50 d 32 C
21 C
32 C
35 42 49 49
d d d d
0.07 –0.02 0.42* 0.31*
0.05 –0.18 –0.21 –0.19
0.26 0.20 0.17 0.34*
–0.44* –0.53* –0.59* –0.60*
–0.04 0.05 0.22 0.16
–0.52* –0.56* –0.34* –0.60*
0.11 0.28* 0.20 0.33*
–0.48* –0.54* –0.36* –0.59*
0.09 0.21 0.05 0.18
–0.49* –0.42* –0.20 –0.47*
35 42 49 49
d d d d
0.27 –0.09 0.32* 0.19
0.15 –0.05 –0.22 –0.13
0.25 0.16 0.12 0.28*
–0.19 –0.37* –0.50* –0.45*
0.06 0.01 0.04 0.05
–0.43* –0.57* –0.19 –0.54*
0.10 0.26 0.07 0.27
–0.26 –0.52* –0.39* –0.55*
0.19 0.24 0.14 0.33*
–0.27* –0.44* –0.18 –0.41*
35 42 49 49
d d d d
0.28* –0.08 –0.28* –0.17
0.06 0.20 –0.05 0.22
0.47* 0.50* 0.20 0.59*
0.16 –0.04 –0.19 –0.14
0.43* 0.40* 0.08 0.57*
–0.06 0.03 –0.13 –0.15
0.53* 0.47* –0.06 0.55*
–0.15 –0.01 –0.20 –0.16
0.08 0.08 –0.08 0.13
0.51* 0.33* –0.22 0.46*
*P < 0.05.
In Replicate 1, the mean correlation between body temperature (at 35, 42, 46, 48, and 49 d) and the 35 to 42 and 42 to 49 d gain was –0.40 and the median was –0.48 for the 32 C environment as compared to a mean of 0.08 and a median of 0.06 for the same correlations in the 21 C environment. The mean correlation between body temperature and the 35 to 42 and 42 to 49 d feed consumption was –0.31 and the median was –0.32 for the 32 C environment as compared to a mean of 0.09 and a median of 0.08 for the same correlations in the 21 C environment. The mean correlation between body temperature and the 35 to 42 and 42 to 49 d feed conversion ratio was 0.24 and the median was 0.23 for the 32 C environment as compared to a mean of 0.00 and a median of –0.02 for the same correlations in the 21 C environment. In Replicate 2, the correlations between body temperature (at 35, 46, 48, and 50 d) and gain, feed consumption, and feed conversion ratio were similar to those of Replicate 1 with the exception of the 42 to 49 d feed conversion ratio, which is probably due to the decreased growth of the birds in Replicate 2 during the 42 to 49 d period. In Replicate 2, the mean correlation between body temperature and the 35 to 42 and 42 to 49 d gain was –0.44 and the median was –0.48 for the 32 C environment, as compared to a mean of 0.17 and a median of 0.21 for the same correlations in the 21 C environment. The mean correlation between body temperature and the 35 to 42 and 42 to 49 d feed consumption was –0.40 and the median was –0.42 for the 32 C environment as compared to a mean of 0.13 and a median of 0.13 for the same correlations in the 21 C environment. The mean correlation between body temperature and the 35 to 42 d feed conversion ratio was 0.43 and the median was 0.37 for the 32 C environment as compared to a mean of 0.02 and a median of 0.02 for the same correlations in the 21 C environment. The mean correlations between the body temperature and the 42 to 49 d feed conversion ratio was 0.00 and the median was
0.01 for the 32 C environment as compared to a mean of –0.15 and a median of –0.16 for the same correlations in the 21 C environment. These results indicate a lack of association between body temperature and traits of economic importance in broilers in a normal (21 C) environment. However, when exposed to a heat stress environment there is a strong negative correlation between body temperature and traits of economic importance after 1 wk of heat stress exposure.
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