Thermoneutral zone and resting metabolic rate of broilers

1. Metabolic rate was determined once a week in broilers from a commercial source, from 1 to 63 d of age.

2. The equations relating minimal resting metabolic rate (oxygen consumption, ml/bird h,y) and body weight (W) were: males 45 to 497 g, y = 3.2 W^0.882 597 to 3000 g, y = 40.5 W^0.483; females 45 to 514 g, y = 2.52 W^0.881; 514 to 2500 g,y = 12.3 W^0.627.

3. The relationship between lower critical temperature (T_cl , °C,y) and age (d, x) may be described by the following equations: chicks 1 to 21 d, y = 34.2 ‐ 0.32 x; 14 to 63 d,y = 49.4 × ^?0194.

4. The relationship between T_cl and W may be described by one equation for both sexes between 100 and 3000 g, y = 62.15 W^?0.135..

5. The equations for T_cl and data for upper critical temperature (T_cu ) could be used to obtain maximal performance from broilers, with reduced costs, by providing a suitable environment related to age or body weight.