Use of limited daily access to food in measuring the heat production associated with food intake in laying hens.

1. Two experiments were carried out to determine the heat production associated with food intake in laying hens allowed access to food for one (experiment 2) or two hours (experiment 1) daily. 2. In experiment 1, heat production in the fed state was measured for two successive days after 46 h of food deprivation. The rate of heat production in the fasting state was measured from 47 to 69 h after feeding. 3. In experiment 2, heat production was measured at 4 fixed food intakes: 100, 70, 40 and 0 g/bird. Heat production associated with food intake, eating activity, net availability of ME and maintenance ME requirement was estimated. 4. Heat production after 46 h of food deprivation did not differ from that after 22 h of deprivation. In the hens receiving 100 g of food, heat production reached the pre-feeding level by 20 h after eating; the hens with lower food intakes reached the pre-feeding level more rapidly. It is suggested that the heat production associated with feeding had been eliminated by 22 h after eating. 5. Heat production associated with feeding was 16% of ME intake. Because the total energy cost of eating activity was only 0.8% of ME intake, the heat production associated with food intake in the limited-access hens came mainly from the effects of digestion, absorption and metabolism of the ingesta. 6. The net availability of ME was estimated to be 0.84. The estimated maintenance ME requirement was 569.6 kJ/kgW0.75 d.