Effects of weaning age on maternal reproduction and offspring health in rhesus monkeys (Macaca mulatta).

A study to systematically evaluate the effect of separation of mother and infant in the first year of life on maternal reproduction and long term offspring health was carried out. This study utilized outdoor harem breeding groups with an average ratio of one male to seven females. Female rhesus monkeys with live born infants (N = 750) were assigned to four weaning groups: 6, 8, 10, and 12 months. Two additional groups (N = 155) were included for comparison of reproductive parameters: females whose infants died at 90 days or less and females that had abortions or stillbirths. Females with infants weaned at 6 months had higher reproductive rates than other groups over the 18-month study period. Weaned infants were removed from the dam's cage and housed with age peers. No effect of weaning age was seen on overall measures of offspring health up to 2 years of age. Mortality and morbidity rates showed no differences between infant groups, although the proportion of trauma treatments increased with weaning age. Weights at 1 year varied with weaning group. These findings showed that infant age at separation from dam affected subsequent maternal reproduction without clinical detriment to infant health in harem groups of rhesus monkeys.