Young pigs were fed on three diets consecutively, each diet being given for 1 week. The diets were given in random order as (g pig feed/kg body-weight): (a) 20, (b) 60, (c) 20 plus a supplement with the energy equivalent of 40 g pig feed/kg. The supplements included desiccated coconut, fish meal and glucose. 2. At the end of each week resting metabolic rate, beginning 12--14 h after feeding, was measured overnight using an open-circuit respiration chamber at thermoneutrality. 3. The oxygen consumption of pigs on the 60 g/kg diet was always higher than on the 20 g/kg diet. The addition of desiccated coconut, or fish meal also increased metabolic rate; whereas with added glucose, O2 consumption tended to be even lower than on 20 g/kg alone. 4. The administration of the beta-blocker propranolol to pigs on ad lib, food intake reduced the rate of overnight resting O2 consumption, measured from 10 until 20 h after feeding, by 12%, but it had no effect on O2 consumption when the intake was 20 g feed/kg. Exposure to mild cold (15 degrees) caused an increase in O2 consumption and this was reduced by 14% after injection of propranolol.
