Heat loss from groups of growing pigs under various conditions of environmental temperature and air movement

Abstract

Continuous measurements of heat loss throughout the 24 hours have been made on groups of pigs living in a large direct calorimeter equipped as a pig pen. Five experiments, each lasting 24 days, were carried out on groups of six pigs each weighing about 20 kg, and these were repeated when body weight was 60 kg on groups of three pigs, chosen from the original six in each case. Each group was exposed initially to an environmental temperature of 20°C for 10 days, followed by either 9°C (two groups at each weight), 30°C (two groups at each weight), or a continuation of 20°C (one group at each weight). In another experiment lasting 66 days a group of four pigs was exposed to 12 and 20°C at two levels of air movement.Heat loss from the groups showed a marked 24-hr cycle, with a maximum n i the afternoon and a minimum in the early morning. The mean amplitude of the cycle at 20°C was 20% of the mean value; this proportion increased at 9 and 12°C.Heat loss was approximately proportional to (body weight)^1·0 over the weight range 17·34 kg, and to (body weight)^0·8 over the weight range 35·54 kg, when food intake increased in proportion to (body weight)^1·0. Over the weight range 55·67 kg, when food intake was constant at 1·83 kg/day per pig, heat loss was proportional to (body weight)^0·4. In both 20 and 60-kg pigs, heat losses showed little difference between 20 and 30°C, but were increased at 9°C.Evaporative loss from the pen, as a proportion of total heat loss, was approximately 21% at 9°C, 29% at 20°C, and 61% at 30°C. Voluntary water intake exhibited a marked 24-hr cycle similar in timing to the heat loss cycle.There was no lasting effect on heat loss associated with raising the mean air movement rate in the pen from 10 to 26 cm/sec.