VARIATION IN BODY-TEMPERATURE RESPONSE OF NAKED NECK AND NORMALLY FEATHERED CHICKENS TO HEAT-STRESS

The effect of the naked neck (Na) gene on basal body temperature (BT) in a 21 C (control) or in a 32 C (chronic heat stress) environment and on change in BT when exposed to acute heat stress conditions (40.5 C) was examined in small and large BW populations. Birds grown at 32 C had a significantly lower basal BT, 8-wk BW, and a significantly smaller change in BT when exposed to 40.5 C than birds grown in 21 C. The small BW birds had a higher basal BT and a smaller change in BT when exposed to acute heat stress than large BW birds. There was no difference in basal BT between naked neck and normal birds in either the small BW (Athens-Canadian randombred) population, or in the large BW broiler population. The Na/Na birds in the small BW population had a significantly greater change in BT when exposed to acute heat stress than Na/na or na/na birds, but no differences were seen among genotypes in the large BW population. In the 21 C environment, naked neck birds seemed to have a greater change in BT than normal birds when exposed to 40.5 C. The difference in BT change was significant in the large BW population but was not significant in the small BW population. Few significant correlations were found between basal BT and 8-wk BW or between change in BT and 8-wk BW. A consistent negative correlation was found between basal BT and change in BT for both populations.