Laboratory rhesus macaque social housing and social changes: Implications for research.

Macaque species, specifically rhesus (Macaca mulatta), are the most common nonhuman primates (NHPs) used in biomedical research due to their suitability as a model of high priority diseases (e.g., HIV, obesity, cognitive aging), cost effective breeding and housing compared to most other NHPs, and close evolutionary relationship to humans. With this close evolutionary relationship, however, is a shared adaptation for a socially stimulating environment, without which both their welfare and suitability as a research model are compromised. While outdoor social group housing provides the best approximation of a social environment that matches the macaque behavioral biology in the wild, this is not always possible at all facilities, where animals may be housed indoors in small groups, in pairs, or alone. Further, animals may experience many housing changes in their lifetime depending on project needs, changes in social status, management needs, or health concerns. Here, we review the evidence for the physiological and health effects of social housing changes and the potential impacts on research outcomes for studies using macaques, particularly rhesus. We situate our review in the context of increasing regulatory pressure for research facilities to both house NHPs socially and mitigate trauma from social aggression. To meet these regulatory requirements and further refine the macaque model for research, significant advances must be made in our understanding and management of rhesus macaque social housing, particularly pair-housing since it is the most common social housing configuration for macaques while on research projects. Because most NHPs are adapted for sociality, a social context is likely important for improving repeatability, reproducibility, and external validity of primate biomedical research. Am. J. Primatol. 79:e22528, 2017.