Female mammals often begin to reproduce before achieving somatic maturity and therefore face tradeoffs between allocating energy to reproduction or their own continued development. Constraints on primiparous females are associated with greater reproductive failure, and first-born infants often have slower growth and greater mortality and morbidity than infants born to multiparous females. Effects of early life investment may persist even after weaning when juveniles are no longer dependent on maternal care and mother’s milk. We investigated the long-term consequences of birth order in a large sample of rhesus macaques, Macaca mulatta, assigned to the outdoor breeding colony at the California National Primate Research Center (N=2724). A joint model for growth and mortality over the first three years of life allowed us to explicitly connect growth rates to survival. As expected, males are born heavier and grow faster relative to females. However, contrary to expectations, later-born males face substantially lower survival probability during their first three years, whereas first-born males survive at greater rates similar to both first-born and later-born females. Primiparous mothers are less likely to conceive during the subsequent breeding season, suggesting that their reproductive costs are greater than those of multiparous mothers. We speculate that compensatory tactics, both behavioral and physiological, of first-born offspring and their mothers, as well as the novel ecology of the captive environment, underlie these findings. The results presented here provide new insights into how maternal and infant life history tradeoffs may influence developmental trajectories even after the period of maternal dependence.

Mother's milk contains numerous hormones and growth factors, which have not been extensively investigated in nonhuman primate milk. Here we report values for several bioactive factors in rhesus macaque milk and describe patterns in concentration across lactation. We used 177 milk samples from 59 macaque mothers (each contributing samples from early, peak, and late lactation) housed in the outdoor breeding colony at the California National Primate Research Center. Using standard parallelism and recovery tests, we validated enzyme immunoassays (R&D Systems, Minneapolis) measuring epidermal growth factor (EGF), its receptor (EGF‐R), adiponectin, transforming growth factor beta‐2 (TGF‐ß2), and insulin‐like growth factor II receptor (IGF‐IIR). Linear mixed models, controlling for total milk volume and repeated measures, show that adiponectin, EGF, and EGF‐R all increased significantly from early to peak, and peak to late lactation. Increases from peak to late lactation were noted in TGF‐ß2 and IGF‐IIR. These results illuminate new pathways for the investigation of early life programming through the transfer of bioactives in milk. Supported by NSF‐BCS‐0921978 (KH) and a GW‐SI Opportunity Fund Grant (RB).