Growth and threshold weaning weights among captive rhesus macaques

Abstract

Interspecific analyses of infant growth and the time to maternal reconception (or weaning) demonstrate a consistent threshold for weaning weight at close to four times neonate weight, irrespective of the duration of lactation (Lee et al., [1991] J. Zool. Lond.225:99–114). Intraspecific variation in the attainment of a threshold weaning weight was determined in a sample of 31 captive infant rhesus macaques, where growth between birth and subsequent parturition was measured along with information on maternal size, weight, and social characteristics. A threshold weaning weight was found, with infants attaining approximately 1,335 g at the time of reconception. Birth weights of the infants were influenced by maternal physical and social variables in that larger mothers, and alpha ranking mothers, produced larger neonates. Postnatal growth rate, which determined the attainment of the threshold weight, was independent of maternal size or condition, but was influenced by offspring sex and the probability of reconception. Future reproductive status of mothers was specifically related to differences in patterns of growth among the infants. Mothers who conceived again at 30 weeks had infants who grew more slowly after the first 12 weeks of life, especially if these infants were sons. Mothers in this colony appeared to make decisions about the need to sustain their infants' growth in relation to their ability to invest in current offspring, which may compromise their subsequent reproduction.