Rectal Temperature Changes in Broilers Kept Under Hot and DryConditions

This study investigated the effects of environmental conditions on rectal temperature of broilers subjected to different heat loss- and heat gain-enhancing treatments. Twenty six-week old broilers with similar body weight were used in the study. The four treatments were allocated to the broilers in a Completely Randomized Design: (і) Beak and Wings Taped (BWT) where birds could not pant or droop wings; (іі) Beak Taped (BT) where birds could not pant; (ііі) Wings Taped (WT) where birds could not droop wings and; (іv) the Control (C) where birds could pant and droop wings. The experiment was replicated five times (5 birds per treatment). The rectal temperature (RT) probes were used to measure RTs of the broilers every 20 seconds during each 8-hour experimental period. Environmental conditions, i.e., air temperature (T); relative humidity (RH); air velocity (V), and duration of heat exposure were measured and used as independent variables in linear regression models of rectal temperature. The resulting models were RTBWT = 0.640T + 0.225RH – 0.578V + 15.223; RTBT = 0.811T + 0.353RH – 0.142V + 5.433; RTWT = 0.257T – 1.288V + 35.602 and RTC = 0.382T + 0.062RH – 1.179V + 29.339. For the latter, the models developed were RTBWT = 0.681t + 41.013; RTBT = 0.775t + 41.410; RTWT = 0.391t + 41.014 and RTC = 0.438t + 40.967. Both panting and drooping of wings were effective in relieving the birds of heat stress. Panting was the dominant heat loss mechanism as air temperature approached or exceeded body temperature of the birds. The birds died at varying degrees of cumulative body heat loads which seemed to depend on the individual bird’s ability to cope with heat stress. The average lethal cumulative heat loads were 7.1, 8.3, 9.0 and 11.0oC-hr for the BWT, BT, WT and C treatments, respectively. For future similar experiments, improvement should be made on the tunnel to accommodate more than one bird per cage.