Comparing options for pair housing rhesus macaques using behavioral welfare measures.

In a biomedical research environment, research or management procedures may render continuous full contact pairing of rhesus macaques (Macaca mulatta) unfeasible. This study aimed to determine whether separation on a frequent basis or housing in adjacent cages with tactile contact interferes with the behavioral benefits of continuous full contact. Behavioral data (1260 hours) were collected from 32 adult females and 16 adult males housed at two National Primate Research Centers. Subjects were studied in four housing conditions: single housing, full contact pair housing, intermittent contact pair housing, and protected contact housing. After introduction, each pair was housed in each of the three social housing conditions in varying order. Among females, but not males, introducing animals into full and intermittent contact reduced levels of abnormal behavior. There was a trend toward this reduction in protected contact. In both females and males, full and intermittent contact was associated with lower levels of anxiety-related behavior, but protected contact was not. Females spent more time inactive in protected contact than either full or intermittent contact, and males showed a trend toward less inactivity following introduction into full contact. Both sexes showed less affiliation in protected contact compared to the other forms of social housing. Agonistic behavior among females was not affected by housing condition; among males, levels were equivalent in full and intermittent contact but were higher in intermittent than protected contact. Frequent separation of pairs does not appear to detract from the behavioral benefits of pair housing. Separation by a barrier permitting tactile contact is inferior to other forms of social housing but showed modest improvements over single housing nonetheless. This study can guide the provision of social contact to rhesus macaques under conditions restricting pairs from continuous full contact.

Benefits of pair housing are consistent across a diverse population of rhesus macaques.

Introducing singly housed rhesus macaques (Macaca mulatta) into isosexual pairs is widely considered to improve welfare. The population of laboratory rhesus macaques is heterogeneous on a variety of factors and there is little literature available to directly evaluate the influence of many of these factors on the benefits of pair housing. Subjects were 46 adult female and 18 adult male rhesus macaques housed at the Tulane National Primate Research Center and the Yerkes National Primate Research Center. Behavioral data totalling 859 h and serum cortisol levels derived from 312 serum samples were analyzed for main effects of housing condition, comparing single housing to pair housing. In addition, a series of analyses were performed to test for interactions between housing condition and seven independent variables: sex, age, prior duration of single housing, presence or absence of a history of self-injurious behavior, and dominance rank, levels of affiliation and agonism in the paired setting. After the collection of 4-8 h of baseline data and three serum cortisol samples, pairs of individuals were introduced to one another and data collection was repeated, no earlier than 4 weeks after introduction. In pair housing both female and male subjects showed decrease in abnormal behavior (females: 54% reduction; P = 0.001; males: 18% reduction; P = 0.0007) and anxiety-related behavior (females: 35% reduction; P = 0.0001; males: 41% reduction; P = 0.0001), and increases in locomotion (females: 41% increase; P = 0.0001; males: 76% increase: P = 0.002). In pair housing, there were no significant sex differences in social behavior. Descriptively, paired females spent 12% of samples engaged in affiliative behavior and 0.5% engaged in agonistic behavior (back-transformed arcsin square root means). The corresponding values for males were 12% and 0.3%. No interaction effects were detected with any of the independent variables tested in this study. Cortisol values varied with sex but did not differ between housing conditions; no differences were detected when any of the above variables were included in the statistical model. Results support the general consensus among those studying the welfare of captive primates that social housing is a potent means for promoting behavioral indicators of the psychological well-being of laboratory primates. These results are of considerable practical significance and include information that refutes common perceptions about the unsuitability of males as socialization candidates, perceived negative.

Positive reinforcement training moderates only high levels of abnormal behavior in singly housed rhesus macaques.

This study evaluated the application of positive reinforcement training (PRT) as an intervention for abnormal behaviors in singly housed laboratory rhesus macaques at 2 large primate facilities. Training involved basic control behaviors and body-part presentation. The study compared baseline behavioral data on 30 adult males and 33 adult females compared with 3 treatment phases presented in counterbalanced order: 6 min per week of PRT, 20 or 40 min per week of PRT, and 6 min per week of unstructured human interaction (HI). Within-subject parametric tests detected no main or interaction effects involving experimental phase. However, among a subset of subjects with levels of abnormal in the top quartile of the range (n = 15), abnormal behavior was reduced from 35% to 25% of samples with PRT but not with HI. These results suggest that short durations of PRT applied as enrichment for this species and in this context may not in itself be sufficient intervention for abnormal behavior because levels remained high. However, it may be appropriate as an adjunct to other interventions and may be best targeted to the most severely affected individuals.