The effect of body temperature on the growth rate of broilers.

The effect of body temperature (Tb) on the growth rate of male broilers was studied. Two pens (5 m2 each), one (A) near air inlets and one (B) near air outlets, were erected in a 12.5 m wide cross-ventilated, environmentally-controlled poultry house. Of 100 birds of both sexes in each pen, 18 males were marked and weighed weekly, and in three of these in each pen body temperature was measured by telemetry over 24 h at 50, 54, 55, 58, and 62 d of age. At 62 d group B birds weighed 250 g less than A; implanted birds weighed less than their group means, but relative growth rates were similar. Mean lowest (08.00 to 09.00 h) and highest Tb (11.00 to 17.00 h) in group A were 41.35 degrees C and 42.13 degrees C, and in group B 41.48 degrees C and 42.86 degrees C, respectively. The regression of G (percentage gain in body weight/d) on noon maximum Tb (Tbn) was G = 46.25 - 1.024 Tbn. This study suggests that an air temperature above 32 degrees C depresses body-weight gain of broilers by about 10% between 5 and 9 weeks of age. Therefore, house temperature should not be allowed to increase above 28 degrees C, except if relative humidity also increases to 0.70 or more.