Effects of Continuous and Intermittent Social Contact on the Welfare of Laboratory Rhesus Macaques (Macaca mulatta)

ABSTRACT

This study evaluated the effects of continuous full‐contact (CFC) versus intermittent contact (IC) housing on the welfare of adult female rhesus macaques ( Macaca mulatta ) in a laboratory breeding colony. Twenty‐four females from the California National Primate Research Center Time Mate Breeding Colony were assigned to CFC pairs with uninterrupted social access or to IC pairs separated for approximately 18 h daily. Behavioral observations collected over 5 months quantified affiliative, aggressive, anxious, and abnormal behaviors. Across the full day, macaques in CFC pairs exhibited higher rates of affiliative behavior than those in IC housing. IC pairs showed marked increases in abnormal behavior during separation periods, while the association between separation and anxiety‐related behavior varied according to cage level. Analyses accounting for social contact availability indicated that increased abnormal behavior was specifically associated with periods of single housing. In contrast, no behavioral differences between housing groups were detected when both groups were observed under equivalent full‐contact conditions. Aggressive behavior was more frequent in bottom‐tier than top‐tier cages, indicating that cage location may influence behavioral outcomes. Importantly, successful conception in females housed in CFC suggests that routine reproductive monitoring remained feasible under continuous full‐contact housing conditions. These findings indicate that housing conditions providing continuous access to a social partner are associated with improved welfare compared to regimes that include repeated daily separation and suggest that routine separation practices may warrant reevaluation. Where feasible, CFC housing should be considered the preferred social housing strategy for laboratory rhesus macaques.