Some Physiological Responses of Turkeys Selected for High and Low Adrenal Response to Cold Stress

Two lines were developed from the Ohio Randombred Control (RBC) population on the basis of their plasma corticosterone level after cold stress. One line (HL) was selected for increased plasma corticosterone, while the other line (LL) was selected for low corticosterone level after cold stress. By the F6 generation the mean corticosterone level after cold stress of the HL (14.8 (μg.%) was nearly double that of the LL (7.6 μg.%). Correlated responses measured were body weight, egg production, fertility, hatchability, resistance to disease, response to ACTH, and response to heat stress. At four weeks of age the LL was significantly heavier than the RBC or the HL birds in all generations. The LL birds produced significantly more eggs than the RBC or HL birds after the 4th generation. Although there were few significant differences among lines for fertility and hatchability, the trend was toward slightly better reproductive performance for the LL. This, coupled with better egg production, resulted in superior over-all reproductive performance for the LL. Both natural mortality and mortality due to cold stress and blood collection were significantly lower in the LL than in the RBC and the HL for the F3 through F7 generations. In addition, it appears that the response to cold stress is negatively correlated with resistance to Mycoplasma meleagridis. The response to heat stress in the HL and the LL birds was similar to that from cold stress indicating that the response was nonspecific. The HL birds were nearly twice as sensitive to ACTH injections as the LL birds. The response to ACTH injections strongly suggests that genetic selection altered the adrenal response to ACTH.