Betaine and Antioxidants Improve Growth Performance, Breast Muscle Development and Ameliorate Thermoregulatory Responses to Cyclic Heat Exposure in Broiler Chickens.

Heat stress (HS) is an environmental stressor challenging poultry production and requires a strategy to cope with it. A total of 288-day-old male broiler chicks were fed with one of the following diets: basal diet, basal with betaine (BET), or with selenium and vitamin E (AOX), or with a combination of BET and AOX, under thermoneutral and cyclic HS. Results showed that HS reduced average daily feed intake (ADFI) ( = 0.01) and average daily gain (ADG) ( < 0.001), and impaired feed conversion ratio (FCR) ( = 0.03) during rearing period (0⁻42 day). BET increased ADG ( = 0.001) and decreased FCR ( = 0.02), whereas AOX had no effects. Breast muscle weight was decreased by HS ( < 0.001) and increased by BET ( < 0.001). Rectal temperature was increased by HS ( < 0.001) and improved by BET overall. Respiration rate was increased by HS ( < 0.001), but BET decreased it during HS ( = 0.04). Jejunum transepithelial resistance was reduced by HS and had no effect on permeability whereas BET increased jejunum permeability ( = 0.013). Overall, the reductions in ADG of broiler chickens during HS were ameliorated by supplementation with BET, with much of the increase in ADG being breast muscle.