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Published online by Cambridge University Press: 27 March 2009
Hens and cockerels of a White Leghorn strain (‘H & N’) were kept at a constant temperature of 23 °C from 1 year until 2¼ years of age. The mean fasting heat production, which was measured 6 times during this period, varied between 404 and 464 kJ/kg0·75/day for the hens and between 223 and 349 kJ/kg0·75/day for the cockerels. The sex difference in heat production is discussed and an attempt is made to explain the variation in heat production for each sex.