Abstract
Water, fat, and lactose concentration were studied at five-day intervals during pregnancy, parturition, and lactation in primiparous rats. A striking finding was the unchanging composition of the fat-free mammary tissue, as indicated by a constant proportion of dry weight for all of the periods studied. Thus, water content remained the same (80%) during pregnancy and lactation. The per cent fat of the gland declined steadily from 67% in the nonpregnant animal to 15% during lactation.Analysis of rat milk revealed fat and solids-not-fat concentrations to be about 13 and 17%, respectively. Lactose was found to be present in low amounts in the pregnant nonlactating gland, and to rise sharply at parturition. Both tissue lactose and milk lactose concentration rose significantly as lactation progressed, tissue values going from 596 μg/100mg on Day 1 to 939 μg/100mg on Day 20, and milk lactose from 12.3 mg/ml on the first day to 18.1 mg/ml on Day 15. Fresh gland weight, when corrected for the estimated amount of milk retained, was found to be essentially constant during mid-lactation. A micro milking apparatus is described.
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