Lactation Activity, Chemical Composition, and in vitro Metabolism of Rat Mammary Tissue

SummaryMammary tissue of rats at the end of pregnancy and at the height of lactation was analyzed for dry matter and nitrogen content, and the metabolic rate of this tissue was measured in vitro.Lactation increased the water content of the mammary tissue and the protein content of the mammary dry matter.Lactation did not affect the metabolic rate per unit of fresh tissue in vitro; it increased the metabolic rate per unit of dry matter and decreased the metabolic rate per unit of nitrogen in the tissue.Observations were also made on rats that suckled only 1-3 instead of 6 young; and measurements were taken on rats with 6 young at earlier stages of lactation before full milk production was reached. These indicate a positive correlation between the intensity of lactation and the magnitude of the effect that lactation has on the composition and metabolic rate of mammary tissue.