1. Eighteen litters of piglets were weaned at 14 days of age and reared for a further 3 weeks at environmental temperatures of 18, 23 or 28°C. At each environmental temperature three levels of feeding were used. The changes in body composition of the piglets were studied by the comparative slaughter procedure, littermates being analysed at birth, and at 14, 22 and 36 days of age. For comparison, the bodies of suckled piglets of similar weights and ages were also analysed.
2. In the 2 to 3 day period following weaning, body weight decreased, with the greatest reduction being 0·28 (s.e. 002) kg at 18°C. Following this, body weight gain was dependent on both environmental temperature and level of feeding, although at any given level of food intake there was little difference between the values at 23 or 28°C.
3. There were marked changes in the chemical composition of the carcass in relation to the different temperature/feeding level combinations. The most variable component was fat. In the period following weaning there was considerable mobilization of fat, especially at the lower temperatures and feeding levels. The fat content of the early weaned piglets at 36 days of age (68 to 103 g/kg) was significantly less than that of the suckled piglets (169 g/kg) (P < 0·01). The decreases in fat content were accompanied by increases in the dry-matter content of the carcass.
4. The protein content of the carcass remained relatively independent of the different treatments, ranging from 140 to 164 g/kg for the early-weaned piglets, compared with 139 g/kg for those that had suckled their mothers.
5. The differences in the growth and body composition of the early-weaned piglet are discussed in relation to an inadequate food intake following weaning, to changes in nutrient supply and to variations in the climatic environment.