Self-selection of protein during pregnancy and lactation in rats.

Protein self-selection was investigated in female rats throughout pregnancy and lactation. In the first experiment, impregnated rats were presented with either a choice between low and high protein (casein) diets, or standard lab chow and their protein intake was compared to that of non-impregnated controls. Impregnated females showed an increase in both absolute and relative protein intake at the end of pregnancy and during the second week of lactation when compared to both their own baseline intake and that of non-impregnated rats. In the second experiment, lactating rats and non-lactating controls were presented with a choice between low and high protein (casein) diets, a high protein (soybean meal) and a high carbohydrate diet, or lab chow. Lactating rats consumed more protein than non-lactating rats regardless of diet condition, but percentage protein intake was found to differ across diet choice conditions. Differences in diet fraction choice are discussed in terms of protein: carbohydrate ratios, and how different sources of protein might be utilized differently within the body.