I. Eight groups each of four castrated male pigs, 25-30 kg initial body-weight, were kept for periods of 3 weeks in a calorimeter equipped as a pig pen and maintained at either 8" or zoo. At each temperature two feeding levels (g food/kg body-weight per d) were used, 45 and 52 at So, and 39 and 45 at 20'. Metabolizable energy, heat loss and nitrogen balance were measured.2. Heat loss was higher at 8" than at zoo and was independent of plane of nutrition, whereas at 20' the higher heat loss occurred at the higher plane of nutrition. Energy retention depended on both temperature and feeding level, and was highest at the 52 g feeding level at 8".3. N retention was not influenced by environmental temperature but varied with plane of nutrition (correlation coefficient = 094), the increase being 9.98 ( & 0.8) mg N per g food increase. The correlation coefficient between N retention and body-weight gain was also 0'94; body. weight gain was correlated with N retention rather than with fat deposition. Fat gain was reduced at the lower feeding levels and at the lower environmental temperature at the feeding level of 45 g/kg.4. The partial efficiency of energy retention at zoo was 66.5%. From this efficiency the maintenance requirement (at zero energy retention) at zoo was calculated to be 418 kJ/kgo*'5. At 8" the partial efficiency of energy retention was 99.4%.Calorimetric measurements have shown that, in addition to effects associated with body size and thermal insulation, the rate of an animal's heat loss is determined principally by two factors, the plane of nutrition and the environmental temperature. The environmental temperature also determines which of these two factors is primary : in the zone of thermal neutrality, the plane of nutrition is the chief determinant, with the higher heat loss occurring at the higher level of feeding, whereas under cooler conditions heat loss is dependent on the environmental temperature and the plane of nutrition has little effect. This relation has been demonstrated for heat production measured by indirect calorimetry in individual clipped sheep (Graham, Wainman, Blaxter & Armstrong, 1959) and in groups of pigs (Verstegen, 1971), and for heat loss measured by direct calorimetry in groups of pigs (Close, Mount & Start, 1971).In the direct calorimetric experiments on pigs each group was exposed to two consecutive planes of nutrition while the environmental temperature was held constant. In earlier work (Holmes & Mount, 1967), each group had been exposed to two consecutive environmental temperatures while the plane of nutrition was held constant.In both instances at the lowest environmental temperatures used (7 and 9O respectively) at a given level of food intake the rate of heat loss was increased significantly and the rate of energy retention (metabolizable energy intake less heat loss) reduced correspondingly.In both sets of experiments on pigs there was the possibility that the results obtained

SUMMARY1. Rates of heat loss from 12 groups of pigs were measured over 4-week periods in a large direct calorimeter equipped as a pig pen.2. The levels of feeding in different groups were 34, 39, 45 and 52g/kg body weight per day, and the calorimeter temperatures were 7°, 12°, 20° and 30°C.3. At 12°, 20° and 30°C the rates of heat loss were related to the level of feeding.4. At 7°C the mean rate of heat loss was higher than at the other temperatures, and was not related to the level of feeding.

SUMMARYThe voluntary intake of water by 24 groups of 3 to 6 Large White pigs (range of mean body weight: 21 to 73 kg) was measured during a total of 48 periods lasting 3 to 12 weeks each in a large calorimeter equipped as a pig pen. The calorimeter temperature was controlled between 7° and 33°C and the pigs were fed at levels ranging from 42 g feed/kg body weight per day to maximal intake. The mean water: feed ratios were between 2·1 and 2·7 at temperatures between 7° and 22°C, and between 2·8 and 5·0 at 30° and 33°C. The range of mean water consumption extended from 0·092 to 0·184 litre/kg body weight per day.

No abstract