Composition of rat milk from day 5 to 20 of lactation and milk intake of lean and preobese Zucker pups.

Milk composition and milk intake were measured in lean and preobese Zucker rat pups. Lactating dams were injected with 3H2O, which equilibrated with plasma water within 30 minutes. A constant specific activity of 3H was maintained by adding 3H2O to drinking water. Blood samples of 5 microliters were obtained from 1, 15 and 20-day-old suckling pups every 4 hours for a 24-hour period and the accumulation of tritium was used to calculate pups' milk intake. No diurnal variation in milk intake of pups was observed. Obese pups were identified at 5 weeks of age and showed no difference in milk intake compared to lean littermates at 10, 15 and 20 days of age. Milk intake of pups increased with age from 2.0 ml at day 10 to 15.8 ml by day 20. Food and water intake of dams also increased from day 10 to 20 of lactation. The protein and carbohydrate component of rat milk did not change significantly from day 5 to 20 of lactation; however, the fat component decreased significantly from 12.7% at day 5 to 4.2% at day 20.