Abstract
Summary
Litters of primiparous lactating rats were adjusted to contain either 6, 9, or 12 young on the day of parturition. On day 13 postpartum, each rat was isolated from her litter for 16 hrs. On day 14 postpartum, each dam was anesthetized with sodium pentobarbital and weighted. The pups were then returned to their mothers, allowed to suckle the abdominal-inguinal glands, and each dam was reweighed. The difference between the prenursing and postnursing weights of the dam was used as an index of milk yield. Deoxyribonucleic acid (DNA) of the abdominal-inguinal glands was also determined. The DNA content of the glands of rats nursing 9 or 12 young was 22 and 39% greater, respectively, than that of rats nursing 6 offspring. Milk yield by rats nursing the larger litters was also significantly greater. A significant increase in litter weight gain was evident between litters of rats nursing 6 and 12 pups. These data suggested that an increase in the suckling stimulus (larger litters) resulted in an increase in mammary gland cellular content (DNA) which was reflected in an increase in milk yield.
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