Abstract: The experiment was conducted to investigate the effects of early heat stress on the growth and development of broilers and gene expression in skeletal muscle. One hundred and ninety-two (male and female half) healthy newborn AA broiler chickens with similar body weight were randomly divided into 2 groups (4 repetition per group, 24 chickens per repetition):heat stress treatment (heat stress group, 36℃ for 24 h) and normal temperature (control group,33℃ for 24 h) at 3 days of age. At 42 days of age, 8 chickens from each treatment were selected and slaughtered, the plasma was collected, and carcass performance was measured. Pectoralis samples were separated to determine the gene expression related to skeletal muscle development. The results showed that early heat stress significantly decreased the body weight gain of chickens at 3 days of age, but significantly increased the average daily weight gain of broilers during the whole feeding period (P<0.05). Compared with the control group, the average daily intake of broilers during the whole feeding period was increased after early heat stress (0<P<0.1). The early heat stress had no significant effect on the carcass rate, half-clean chamber rate, full-clean chamber rate, liver proportion, heart proportion, pectoral muscle rate, leg muscle rate and abdominal fat rate of broilers (P>0.05). Early heat stress significantly increased the plasma ketone body content of 42-day-old broilers (P<0.05). In pectorals, early heat stress significantly increased the expression of insulin-like growth factor (IGF-1) and its receptor (IGF-1R) genes (P<0.05). The results suggest that early heat stress improves the growth and development of broilers in the later stage, and IGF-1 signals in skeletal muscle may be involved in this regulatory process.

Key words: early heat stress, broilers, growth and development, IGF-1 signal