Multidisciplinary assessment of cumulative experience in laboratory rhesus macaques

Abstract

Rhesus macaques (Macaca mulatta) are widely used in biomedical research due to their phylogenetic proximity to humans and their ability to perform complex cognitive tasks. Optimising their welfare is essential from both an ethical and a scientific perspective. However, welfare concern due to their extensive stays at research facilities is increasing and led to the introduction of the concept of cumulative experience (defined as the net impact of all events that affect adversely, positively and by way of amelioration, the welfare of the animal over its lifetime). The importance of assessing cumulative experience in laboratory macaques has been highlighted in research regulation. To address this need, my thesis aimed to assess the cumulative experience of laboratory rhesus macaques involved in neuroscience experiments and to identify factors that could be impacting it. To accomplish this, I used new, validated behavioural and neuroimaging indicators of cumulative experience, as well as currently used indicators of welfare based on body weight and alopecia. I refined the use of the behaviour Inactive not alert to maximise its sensitivity and specificity as a marker of cumulative experience by testing different durations as well as estimating the number of sessions required to assess reliably the frequency of the behaviour. Neither the neuroimaging indicator nor the weight measures showed any signs of cumulative experience in the study subjects. However, I found an increase in alopecia and the frequency of Inactive not alert behaviour over time. The behavioural data suggest that this latter effect is likely to be caused by experimental procedures. However, the effect is small, compared to other factors known to have a detrimental impact on the welfare of macaques. This is the first study revealing a cumulative negative effect of experimental procedures on laboratory macaques. Implications of these results and next steps are discussed.