Evaluating indicators of wellbeing in captive grey mouse lemurs, Microcebus murinus, in the context of enrichment

Developing and implementing effective approaches to improve the welfare of animals participating in research requires reliable monitoring of their wellbeing. Since wellbeing is a multidimensional state that relates to an individual's physiological, behavioural and psychological/mental health, assessing it requires the use of measures that are both ecologically relevant and species-specific. Grey mouse lemurs are small, nocturnal, arboreal and omnivorous primates and a powerful model for fundamental and translational research. As such, it is important to study the factors that may help predict their wellbeing in captivity. Therefore, we monitored 12 adult mouse lemurs (six females and six males) housed with a same-sex weight-matched cage mate for 5 weeks under standard (Control) levels of environmental enrichment and 12 adults (six females and six males) under relatively High enrichment. We hypothesized that higher structural enrichment would stimulate metabolic energy expenditure, influencing how individuals would respond to a battery of behavioural and physiological measures, especially since their feeding rations remained unchanged throughout the study. We characterized circadian activity, judgement bias, predatory motivation, thermal reactivity to stress and changes in body composition. Generally, mouse lemurs under High enrichment showed more activity and increased predatory motivation and optimism than those in the Control group during daylight. Lemurs under High enrichment also showed increased responses during a stress reactivity test and higher losses in body and fat mass. Principal component analysis identified seven (out of nine) components that explained 96% of the variability in the data. Using a Naïve Bayes classifier algorithm trained with these new principal components, we classified the animals as either from High or Control enrichment levels with 100% accuracy. In summary, by measuring several relevant behavioural and physiological responses to environmental enrichment, we identified a multidimensional effect related to differences in welfare.