The effects of plane of nutrition and environmental temperature on the energy metabolism of the growing pig. 3. The efficiency of energy utilization for maintenance and growth.

1. From the relation between metabolizable energy (ME) intake and heat loss (H), energy retention (ER), protein (P) and fat (F) deposition the energy costs of maintenance (MEm) and the partial efficiencies of energy retention (k) and protein (kP) and fat (kF) retention were determined in growing pigs at environmental temperatures of 10, 15, 20, 25 or 30 degrees. 2. k decreased with increase in environmental temperature from 0.79 at 10 degrees to 0.63 at 30 degrees with 0.67 at the thermally-neutral temperature of 25 degrees. Each 0.04 decrease in k was associated with a 100 kJ/kg0.75 per d decrease in MEm. Analysis, within several ranges of environmental temperature, suggested a curvilinear relation between ER and ME intake indicating a decrease in k with increase in level of feeding, particularly at thermally-neutral temperatures. 3. Both kP and kF were similar at each environmental temperature and decreased from 0.78 at 10 degrees to 0.63 at 30 degrees. These values are discussed in relation to those predicted from experimentation and it is suggested that the wide range of predicted estimates of kF could be attributed to differences in the rate of protein turnover.