DERRICKSON, E.M.; Loyola College: Maternal protein intake during pregnancy and lactation determines milk composition in Mus musculus

Both the quantity and quality of resources available to mammals can strongly influence growth and development of juveniles during the lactation period. Although the quantity of food has demonstrated effects on lactation and reproductive success, the effect of food quality has received more limited attention. Using Mus musculus as a model, I tested whether dietary protein levels would lead to changes in milk protein levels. Primiparous mice were fed a 10% or 20% casein-based diet from one week prior to pairing through two consecutive reproductive attempts. Milk was collected at two stages of lactation during the first and second litters of mice that were either lactating only or concurrently pregnant and lactating. Maternal mass, food consumption, and reproductive parameters were measured throughout the experiment. Mice in both dietary treatments increased their food consumption during lactation, but mice on the 20% diet consumed slightly greater quantities of food. Protein concentration was reduced by 12% in mice fed the 10% diet, and the effect of diet on milk protein was greatest in those females who were concurrently pregnant and lactating during their first litter. Low dietary protein levels are a stressor in the sense that mice cannot maintain constant quality of milk in the face of declining food quality. Although females may try to maintain milk protein levels by utilizing body stores of protein, this study indicates that mass loss is low. Further, females do not seem to compensate for low levels of dietary protein by increasing food consumption. Finally, dietary protein levels had no effect on litter size, neonate mass, litter mass at birth or mortality, which indicates that protein deficiency has very different effects from energy deficiency on reproductive tactics.