Effect of dietary protein and environmental factors on lactation performance in rats.

The effects of dietary protein and environmental conditions on lactation performance in rats were evaluated. Female rats were fed from conception until day 9 of lactation diets containing 21% wheat protein (21W), 21% casein + methionine (21CM) or 11% casein + methionine (11CM). At parturition, dams were kept in their normal environment (20 degrees C) or were exposed to crowded conditions or an elevated ambient temperature (30 degrees C). Feeding poor-quality protein (21W) or a lower amount of high-quality protein (11CM) reduced day 8 pup weights and average daily gains (ADG). Pup ADG's nursed by crowded dams fed either 11CM or 21CM were greater than those of pups nursed by noncrowded dams. Pup ADG's were reduced by heat exposure in dams fed 21CM but not in pups raised by dams fed diets reduced either in protein quality (21W) or protein quantity (11CM). Thus lactation performance was not further reduced by heat exposure in dams fed poor-quality wheat protein in spite of reduced food consumption and increasing lactation weight loss in these dams. The study indicates that lactating rats have considerable ability to raise their litters under potentially adverse conditions.