The body composition of young mammals has been investigated in relation to environmental temperature and energy intake. Piglets were weaned at 14 days and then kept separately at 35 or 10 °C and fed either a high or a low energy intake. The animals were killed at 38, 48, 56 or 64 days of age and the carcass divided into four compartments: superficial tissue (skin and subcutaneous adipose tissue), muscle, contents of abdomen (gastro-intestinal tract, liver and kidneys), contents of thorax (heart and lungs). Each compartment was analysed for fat, nitrogen and energy content.
The results were analysed using a non-orthogonal analysis of variance in oider to investigate the separate effects of environmental temperature and energy intake, to test for possible interactions between these two factors, and to assess the time it takes for any effects to develop.
The total amount of fat stored in the body was greater in the pigs kept at the high temperature than in those kept at the low temperature and increased with an increase in food intake; there was no evidence of an interaction of temperature and diet, suggesting that their effects were exerted independently. The extra fat was stored mainly in the superficial tissue and muscle, but partly also in the deep body compartments. However, when expressed as a percentage of the total fat store a greater proportion was found in the deep body compartments of those kept at the low temperature and on the low intake, although the absolute quantities of fat involved were small.
The nitrogen content was also greater at 35 than at 10 °C, and on the high than low intake. Most of the nitrogen was present in the muscle and the proportion of the total body nitrogen stored here was greater in the warm than in the cold, whereas it was unaffected by energy intake. The energy contents of the tissues measured by bomb calorimetry and estimated from the chemical composition were similar. For animals kept at 35 °C most of the energy was stored in the superficial tissue, with the muscle as the second highest store. By contrast, those in the cold stored most of their energy in the muscle.
The present investigation has thus highlighted the large and partly independent effects that environmental temperature and food intake can have on the distribution of energy within the body and the chemical form in which it is stored.