Physiological responses of tom turkeys to temperature and humidity change with age

1. Using a 3-factor uniform-precision rotatable central composite design, male turkeys at 5 ages (5-20 weeks) subjected to 5 temperatures (T, 25-40 degrees C) and 5 relative humidities (RH, 40-80%) during 2 h exposure periods were assessed for body temperature (BT), moisture production (MPM), CO2 production, respiration rate (RR) and heart rate (HR). Prediction equations based on thermal conditions were developed for each physiological response. 2. For the temperature range selected, RH had a stronger effect than T. Maximum RR occurred at lower T and RR was more variable in older, heavier birds. 3. Twenty-week-old birds used compound ventilation in addition to panting, which may have reduced the severity of heat stress and the consequent lack of a significant change in body temperature. (C) 1997 Elsevier Science Ltd.