Rectal Temperature Changes in Broilers Kept Under Hot and Dry Conditions

H. J. Chepete


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.

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