Effect of peripheral foot cooling on metabolic rate and thermoreregulation of fed and fasted chicken hens in a hot environment.

An experiment with a factorial arrangement of treatments was conducted to determine the effect of ambient and water-cooled roost temperatures on metabolic rates of fasted and fed Columbian Plymouth Rock hens. Indirect open circuit calorimetry was used to determine oxygen consumption and carbon dioxide production rates by the hens. Experiments during the thermoneutral period were conducted at 25 +/- 1 C for both ambient and roost temperature treatments. Experiments during the heat-stress period were conducted at an ambient temperature of 35 +/- 1 C. Roost temperatures of 20 +/- 1 (water-cooled roost) and 34 +/- 1 C were provided. Fasting was for at least 40 h; fed hens were fasted, then gavaged with 20 g of sucrose dissolved in 20 mL of distilled water. The metabolic rates were consistently higher in fed than fasted hens for all temperature treatments. The respiratory quotient responses were significantly influenced by feeding status of hens but not by ambient or roost temperature treatments. Cooled roosts in the 35 +/- 1 C environment provided metabolic rates 19% lower. The rectal temperatures of heat-stressed fasted and fed hens with a 34 +/- 1 C roost were elevated 1.20 and 1.32 C, respectively, whereas those of hens with the 20 +/- 1 C water-cooled roosts increased only .22 and .28 C during the heat-stress period, respectively. Hens on the 20 +/- 1 C roost did not initiate thermal panting, whereas those on the 34 +/- 1 C roost panted vigorously. It is concluded that the water-cooled roost partially alleviated heat stress by lowering metabolic rate.(ABSTRACT TRUNCATED AT 250 WORDS)