Effect of ambient temperature on the energy requirements of the lactating rat.

The effect of ambient temperature on the energy requirements of the lactating rat was investigated. Ambient temperature was maintained at 13, 20 or 25 degrees C during lactation, and digestible energy (DE) intake, milk output and energy balance were measured between 4 and 12 d post partum. Ambient temperature did not significantly affect DE intake. Milk output was highest in the rats housed at 13 degrees C and lowest in those kept at 25 degrees C, although the rate of body fat mobilization was lowest in the rats kept at 20 degrees C and highest in the rats kept at 25 degrees C. Energy expenditure on activity and maintenance, determined from the difference between DE intake and body nutrient mobilization plus the energy used for milk production, was significantly higher in the rats housed at 25 degrees C than in those kept at 13 degrees C. This is an opposite trend to that which occurs in nonlactating rats. The results indicate that the gross efficiency of energy utilization during lactation is higher at 13 degrees C than it is at 25 degrees C in the rat.