The proposed project will address two important questions: (1) How does maternal physiological and social condition affect lactational investment as measured by milk composition, milk yield, and nursing behavior? and (2) How do differences in lactational investment affect infant outcomes? Currently little is known about the factors that influence the primary form of maternal investment in non-human primates, the mobilization of maternal bodily reserves for lactation. Several studies demonstrate that some milk constituents, particularly fat, have high inter-individual variation, but the source and magnitude of individual differences have not been explained. The proposed study will assess the relationship between maternal age, health and lactation in 75 captive rhesus macaques housed at the California National Primate Research Center (CNPRC). Comparisons of milk quality, nursing behavior, and infant outcome in young and prime age mothers in good or poor health will indicate how mothers manipulate investment in relation to their own physiological condition. These data will provide systematic information about how maternal nursing behavior and physiological investment affect infant growth and activity. This study will explore fundamental aspects of lactation that have previously not been investigated, and advance our understanding of how selection has shaped maternal reproductive strategies. The data from this study will inform a critical global issue affecting the health of human mothers and their infants. Breastfeeding rates in the US and throughout the world are significantly below optimum, contributing to long-term deleterious developmental and health consequences for the infant. Advances in understanding how rhesus mothers are constrained by health and growth during lactation under controlled research conditions will provide insight into similar challenges for human mothers and provide vital information for current global health concerns. This study will provide a framework for collaboration with researchers working from evolutionary perspectives and mechanistic explanations. Additionally, once a better understanding of maternal condition and milk composition is achieved, targeted studies can be implemented with populations under natural ecological conditions, facilitating international collaboration on future research projects.
