Sleep quality in cynomolgus macaques (Macaca fascicularis) varies by housing type and following surgery

Sleep is an important contributor to good physical and mental health and an important component of postsurgical recovery. The assessment of dark phase ('nighttime') behavior can provide insight into the efficacy of analgesic treatments and should be considered when assessing pain mitigation in animals. This study aimed to characterize dark phase behaviors and sleep patterns in healthy, young adult cynomolgus macaques (Macaca fascicularis) maintained in research settings in either pens or cages. It was hypothesized that primates housed in pens would sleep more deeply (as evidenced by reduced activity) and that despite the use of a robust analgesic program, breakthrough pain or discomfort would occur in post -surgical animals, resulting in reduced sleep, and more activity and pain -associated behaviors compared to baseline. Macaques housed in cages (n=43 across 19 cages) were filmed during a 12 h dark phase before and following telemetry instrumentation surgery. A sampling strategy was determined (15 min/h) and video recordings were randomized, blinded, and scored by trained observers using Observer XT, following an ethogram. Cynomolgus macaques housed in pens (n=21 across 9 cages) were video recorded during a 12 h dark phase for comparison. Descriptive analysis and linear mixed models, as well as a pairwise comparison were used to analyze behavior data. Primates housed in pens were more active in the first hour of the dark period and then largely were inactive and quiet for the rest of the dark phase whereas primates in cages initially settled but became more active for the last 7 h of the dark phase. Following surgery, primates were significantly more active during the post -operative dark phase for up to 5 h (p<0.05) and they engaged in significantly more pain -associated behaviors (p<0.05) compared to pre -operative behaviors. The proportion of social behavior observed was high across the dark phase for both housing systems as well as for animals post -surgery, emphasizing the importance of huddling or clasping of a social partner for comfort during sleep or following surgery in cynomolgus macaques. These results inform recommendations for housing as well as optimal post -operative care specific to the dark phase of research macaques to enhance recovery, welfare, and scientific outcomes.