Effect of heat stress on the performance and some blood parameters in pair-fed broiler chickens

The effects of heat stress on the performance and blood parameters in pair-fed and force-fed broilers were investigated to partition the effects of high temperature and feed intake in chickens. The chicks were housed in two Petersime battery cages. In experiment 1, one battery was exposed to hot cycling temperature (HT) of 25-32°C and the other to a constant temperature (CT) of 22°C. In the second trial, one battery was exposed to HT of 26-34°C and the other to a CT of 23°C. In experiment 3, one battery was exposed to HT of 25-36°C and the other to a CT of 24°C. In all trials, the treatments consisted of feeding a diet ad libitum to a CT ad libitum group of chicks reared under CT condition. Chicks in treatment 2 (HT forcefeeding) were housed in the HT condition and force-fed the amount of intake of birds fed the CT ad libitum diet. Chicks in treatment 3 (HT ad libitum) were fed the diet ad libitum under HT condition and birds in treatment 4 (CT pair-feeding) were housed under CT, and pair-fed the diet at the level of intake of chicks fed the HT ad libitum diet. Results showed that HT birds, force-fed, gained 18, 20 and 33% less weight in experiment 1, 2 and 3, respectively, while HT ad libitum birds gained 11, 26 and 27% less weight in trials 1, 2 and 3, respectively. CT pair-feeding birds gained about 9% less than HT ad libitum birds in all three trials. Based on trial 1 and 2 results, it is estimated that approximately 20% of the reduction in broiler weight gain was due to high temperature per se.