Does behaviour predict weight gain during adulthood in captive group-living rhesus macaques?

Many non-human primates (NHPs) in captivity become overweight. Individual variation in adiposity may result from differences in behaviour related to energy intake, energy expenditure and dominance rank. Understanding how behaviour contributes to becoming overweight may provide opportunities to improve housing and husbandry of captive group-living NHPs. This study therefore investigated whether behaviour predicts weight gain during adulthood in captive female rhesus macaques (Macaca mulatta) housed in three social groups at the Biomedical Primate Research Centre in Rijswijk, the Netherlands. Relative adiposity was quantified with a species-specific weight-for-height index (WHI) during three consecutive annual health checks. Behavioural data were collected at baseline on food intake, activity budgets and dominance rank. We examined which factors were associated with WHI at baseline and whether behaviour predicted the subsequent change in WHI over time, while controlling for individual characteristics. At baseline, a high WHI was associated with low activity levels, but not related to food intake, age or dominance rank. WHI did not differ from baseline after one year but had significantly increased after the second year. This increase in WHI was independent of food intake and activity budgets, while higher-ranking females had a higher increase in WHI compared to lower-ranking monkeys. This suggests that captive NHPs with a high dominance rank are more prone to becoming overweight, whereas differences in activity budgets are merely a consequence and not a cause. Thus, dominance rank, but not behaviour, likely predicts weight gain during adulthood in captive group-living NHPs.