No Effect of Infant Nursery Rearing on Laboratory Rhesus Monkey Dams' Social Behavior or Long-Term Cortisol Profiles

Abstract

While the behavioral and physiological impacts of nursery rearing in laboratory-housed infant monkeys have been well characterized, to date no studies have examined the impact on nonhuman primate dams of their infants being removed for rearing in the nursery. Despite the lack of evidence on the topic, anti-animal research groups often cite mother-infant separation and infant nursery rearing (NR) as a welfare concern for laboratory monkey mothers. As such, important policy decisions regarding research activities may result without adequate evidence. Therefore, we designed this study to examine behavioral and hormonal responses in laboratory monkey dams, who were part of independent long-term longitudinal studies, in response to their infants being NR or mother-peer-reared (MPR). We assessed social, self-care, environmental exploration, and abnormal behaviors for 30 days before and 30 days after parturition in rhesus monkey dams (Macaca mulatta, N=49). Infants were randomly assigned to be either NR (N = 27) or MPR (N = 22). We also analyzed hair samples for cortisol concentrations three times across the study period (Pregnancy, Neonatal Period, Peak Lactation). Dams of NR infants showed no gross behavioral differences relative to dams of MPR infants (all p's>0.05). Dams of MPR infants showed expected increases in social grooming and social contact, and concomitant decreases in foraging and locomotion, in the 30 days post-partum compared to the 30 days pre-partum (p<0.01). Dams whose infants were NR or MPR showed no differences in hair cortisol concentrations across the study period (p>0.05). We conclude that, with respect to the behavioral and endocrine measures we assessed, nursery rearing of their infants is not detrimental to the welfare of laboratory-housed macaque dams.

Keywords: behavior; cortisol; primate; rearing; stress; welfare.