Effect of heat stress early in life on mortality of broilers exposed to high environmental temperatures just prior to marketing.

A study was conducted to investigate the effects of heat stress during the 1st wk of life on subsequent mortality resulting from exposure to high environmental temperature and feed restriction just prior to marketing of broiler cockerels. Birds were raised under standard husbandry procedures except that at 5 days of age, half the broilers were heat stressed by exposure to an environmental temperature ranging from 35.0 to 37.8 C for 24 h while the remaining birds were held at 29.4 C. At 44 and 45 days of age, half the unstressed controls and half the birds stressed at 5 days of age were exposed to temperatures ranging from 35.0 to 37.8 C for 8 h/day. In a factorial arrangement of treatments, the effect of restricting feed for 8 h/day on Days 43, 44, and 45 was also examined. Exposing birds to high environmental temperatures at 5 days of age resulted in a significant decrease in mortality when birds were exposed to a high environmental temperature later in life. In addition, feed efficiency was improved significantly in early heat-stressed birds whereas body weight and body weight gain were not affected. Feed restriction had no significant effect on mortality, body weight, or feed efficiency. It appears, therefore, that exposing broiler cockerels to mild heat stress for 24 h at 5 days of age can significantly decrease mortality resulting from high environmental temperature later in life.