The effects of environmental temperature and plane of nutrition on heat loss, energy retention and deposition of protein and fat in groups of growing pigs.

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%.