The effect of temperature on the heat production, of temperature-acclimatized feathered and defeathered cockerels was examined at 15, 22, 25, 29, 34 and 38 °C. The maintenance ME requirements and the net availability of ME (NAME) were determined for each temperature.
The fasting heat production of defeathered cockerels measured at 22, 29, 34 and 38 °C, decreased continually with increasing temperature. The feathered cockerels also showed a general decrease in fasting heat production with increasing temperature between 15 and 34 °C, but there were relative increases in fasting heat production between 22 and 29 °C.
The ME requirement for maintenance and the NAME were determined from measurements of heat production at different levels of ME intake. In general, the maintenance ME requirement decreased with increasing temperature for both feathered and defeathered cockerels. The NAME for the defeathered birds varied between 75 and 77% at 29, 34 and 38 °C. There was evidence for the feathered birds of an increasing NAME with increasing temperature, one feathered bird having a NAME of 56% at 15°C, increasing to 81% at 34 °C.
The importance of feathering and environmental temperature on the heat production and the possible effect of feather cover and activity on the NAME are discussed.