International Journal of Comparative Psychology

Studies of milk allocation in polytocous species provide the opportunity to investigate the effects of offspring number and sex ratio on maternal investment. In these species maternal control over milk allocation is more difficult because physiological limits on milk production may stimulate sibling competition. This study investigated the nursing behavior of domestic goats bearing twins or singletons in an experimental situation for the first 47 days post-partum. Milk yield and composition did not correlate with litter size, kid weight, or with the behavior of kids. Males were heavier than females, but there were no sex differences in behaviors related to nursing. Milk allocation differences existed between twins and singletons, even though, on the average, there were no significant weight differences. However, one twin was always larger than the other. Twins spent less time in proximity to the mother than did the singletons, and were more responsible for achieving proximity to the mother. These results suggest that nursing behavior was more affected by litter size than by sex of young, although there might be an interaction between both, that early mother-young interactions were different for twins and singletons, and that kids played an active role in the allocation of milk and its conversion to body weight.