From day 1–7 of age, all chicks were raised at 32 ± 1◦C. However, from day 8–35 of age, two groups, including one basal diet group and one NAC-diet group, were exposed to 36 ± 1◦C (from 0800 to 1800) and 26 ± 1◦C (from 1800 to 0800) as cyclic heat stress groups.