Nutritional and environmental factors affecting gestation length in rhesus monkeys.

Forty-five pregnancies in rhesus monkeys maintained in a semioutdoor environment and fed about 1, 2, or 4 g of protein/kilogram of body weight each day in otherwise equivalent diets were observed. The 4-g diet shortened gestation 8.5 days. Male infants were carried 6 days longer than females; part of difference can be attributed to their greater birthweight. Summer conception produced longer gestation than did winter conception. Large mothers carried their infants slightly longer than small ones.