Fat or fit: correlates, consequences and control of overweight in group-housed primates

Primates are highly social animals and should ideally be housed together with conspecifics in social groups. Although group-housing enhances the psychological wellbeing of captive primates, it also leads to an inherent risk of some individuals becoming overweight. Indeed, overweight occurs in almost a quarter of group-housed primates. Measuring and monitoring overweight is important because overweight primates (1) perform less natural behaviour and (2) have a higher risk of health problems. The best way to measure overweight in group-housed primates is a species-specific weight-for-height index. Measuring this non-invasively minimizes disturbances to the primates. Variation in body weight can be measured non-invasively by letting individuals voluntarily step on a scale in their home enclosure. In the colony of the Biomedical Primate Research Centre (BPRC) in Rijswijk, overweight cannot be explained by differences in housing condition, stress levels or behaviour of the primates, while the natural dominance rank has a strong effect. This complicates the application of husbandry strategies to reduce overweight as social organization and dominance rank should not be disrupted. Overweight prevention should therefore be favored over overweight reduction, and this can be achieved by providing diets that mimic the natural diets of wild primates with regard to provisioning, composition and amount of food. Altogether, this thesis provides insight in the correlates, consequences and control of overweight in group-housed primates. Having an overweight management program is recommended for all facilities housing primates to ensure good primate welfare.