Thermoregulation in chicks originating from breeder flocks of two different ages

In the broiler it is recognized that chick viability is related to breeder flock age. Young flocks produce eggs with a lower hatchability and chick su rvival than flocks beyond peak production. Field observations indicate that problems occur when chicks originating from younger flocks are mixed with chicks from older flocks and reared together, perhaps because of a differen ce in thermoregulation. In this experiment, heat production, rectal tempera ture after heat or cold stress, and T-3 of chicks originating from two diff erent aged parent stocks were determined. Chickens originating from older b reeder flocks showed a remarkably better body weight and better thermoregul ation after cold treatment than chickens originating from young breeder flo cks. In contrast, chicks from young breeder flocks seem to be more resistan t to heat at an older age. This implies that age of breeder flock alone can cause a significant difference in the thermoregulatory ability of broiler chickens. Thus breeder flock age should be considered as an additional fact or in thermoregulatory experiments. It also may have practical husbandry im plications.