The effect of dietary protein concentration and quality on the hormonal status, protein metabolism and milk protein concentrations of rats.

Lactating rats were fed casein or cereal protein at one of two concentrations. Milk volume was severely reduced by poor dietary protein quality. Milk fat, lactose and free amino acid nitrogen were unaffected by the diets, whereas total milk protein was reduced by 20% on the cereal diets. Lactalbumin concentrations showed a greater decrease than that of other milk proteins. Changes in maternal serum insulin, corticosterone, albumin and body weight suggest maternal metabolism changes to provide substrate for milk synthesis. Total milk protein and serum albumin synthesis show similar sensitivity to dietary protein adequacy.