Physiologic Consequences of Housing Adult Male Cynomolgus Monkeys (<i>Macaca fascicularis</i>) in Heterosexual Pairs: A Pilot Study Using Implanted Biotelemetry

Facilities may forgo attempting to socially house adult males due to fear of animal injury, study disruptions, and confounding data results. To leverage the potential advantages of male-female pairs, and to understand the impact on measures typically used in safety pharmacology studies, we measured activity as well as physiologic parameters in vasectomized male-female pairs: heart rate, blood pressure, and body temperature. Seven singly housed males that were previously implanted with telemetry were vasectomized and paired with females. Data were collected before and after pairing at specific timepoints in the first study. A second study employed four nonvasectomized, singly housed males to determine if the physiologic effects observed in the first study could be due simply to the increased cage size due to pairing. Results indicated that pair-housing with a female resulted immediately in a significant increase in blood pressure, body temperature, and heart rate. Over the course of a week of being paired, the males showed a significant decline in blood pressure; body temperature remained elevated, though at a lower level than during the immediate response. The second study suggested that increased cage size alone could not account for the immediate results in Experiment 1, inasmuch as no effects were found on our measures. Although the sample sizes for the studies were small, we discuss how our results are similar to, and differ from, previous studies, as well as the clinical significance and welfare implications. This information may be useful in designing long-term studies using sexually mature males while providing stable social support to animals.