The effects of predictability in daily husbandry routines on captive rhesus macaques (Macaca mulatta)

Rhesus macaques (Macaca mulatta) housed indoors experience many routine husbandry activities on a daily basis. The anticipation of these events can lead to stress, regardless of whether the events themselves are positive or aversive in nature. The specific goal of this study was to identify whether increasing the predictability of husbandry events could decrease stress and anxiety in captive rhesus macaques. This study was conducted on 39 single-housed subjects in four indoor rooms at the Oregon National Primate Research Center. Temporal and signaled predictability were added to four daily husbandry events: morning and afternoon feeding, enrichment distribution, and room cleaning. Temporally predictable husbandry events occurred reliably at the same time daily, while signaled predictable husbandry events were preceded by a distinct event-specific signal in the form of a doorbell. Informal tests prior to study onset found the doorbells not to be aversive to the subjects. Subjects received each of four treatments: unpredictable events, temporally predictable events, signaled predictable events, and temporally and signaled predictable events. Change in stress was evaluated by monitoring changes in motor stereotypies and displacement behaviors. Our results showed that subjects displayed less stress and anticipatory behaviors related to feeding and enrichment events when the events were temporally predictable (P<0.0001). When husbandry events were preceded by a reliable signal, subjects vocalized less prior to the event and were less responsive to activity outside of the room (P<0.01). However this may have come at a cost as the animals were extremely reactive to the doorbell signals and showed a heightened stress response during the actual husbandry events (P<0.01). Similar to temporal predictability alone, when temporal predictability was combined with signaled predictability subjects displayed less stress and anticipatory behaviors related to feeding and enrichment events (P<0.0001). In addition, when both forms of predictability were combined subjects showed less stress behaviors while waiting for daily room cleaning (P<0.01). When signaled predictability was paired with temporal predictability subjects no longer had the negative response to the doorbell signal, as they were able to predict and anticipate when the events would occur. Because these results are not necessarily applicable to animals that are given control over their environment or housed in a group setting, the management recommendation that can be made from this study is that temporal predictability of feeding reduces stress and anxiety and is thus beneficial to captive indoor single-housed rhesus macaques.