RESPONSE OF TURKEYS TO RELATIVE-HUMIDITY AT HIGH AMBIENT-TEMPERATURE

1. The effects of relative humidity on growth rate and thermoregulatio n at high ambient temperature were evaluated in turkeys. Male turkeys were exposed to ambient temperature (T-a) of 35 degrees C and relative humidity (RH) of 40% to 75% and 50% to 85%, at ages of 13 to 19 weeks (trial 1) and 10 to 15 weeks (trial 2) respectively. 2. Body weight a nd food intake in both trials increased as RH increased up to 70% to 7 5%. When RH increased further to 80% to 85% (Trial 2) both body weight and food intake declined significantly. 3. Blood CO2 partial pressure (pCO(2)) did not change significantly at different RHs (trial 1). How ever, in trial 2 it dropped significantly at 80% to 85% RH. This respo nse coincided with an increase in blood pH. 4. The effect of RH on bod y temperature (T-b) was not significant in either trial. 5. Triiodothy ronine (T-3) concentrations increased with the increase in RFI up to 7 0% to 75% RH (trials 1 and 2). A significant decrease was observed whe n RH was further increased to 80% to 85% RH (Trial 2). Positive linear correlations between T-3 and food intake or weight gain were observed in both trials. 6. The results indicate that turkeys can thermoregula te efficiently in the face of extreme changes in RH and that only at h igh RH (above 75%) did the performance of turkeys deteriorate.