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

Abstract

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

Evaluation of environmental and intrinsic factors that contribute to stereotypic behavior in captive rhesus macaques ( Macaca mulatta )

“…These results were not surprising; several studies have found that single housed macaques are more likely to display anxiety and abnormal behaviors, including MSB, compared pair housed animals (Baker et al, 2012a; Baker et al, 2013; Gottlieb et al, 2013a; Schapiro et al, 1996). What was somewhat surprising was the finding that animals housed in protected contact showed the same amount of MSB as single housed monkeys.…”

“…Compared to single housing, full contact pairing, in which two animals live in two adjoined cages, has reliably been shown to correlate with decreased expression of MSB in rhesus monkeys (Baker et al, 2012a; Baker et al, 2013; Gottlieb et al, 2013a; Lutz et al, 2003). In contrast, protected contact, a kind of housing in which two NHPs are separated by a partially open divider that allows some tactile contact, has not always shown the same reduction.…”

Factors influencing alopecia and hair cortisol in rhesus macaques (Macaca mulatta)

“…In addition, some patterns of alopecia have been reported to match cage mesh patterns and may be due to the friction caused by leaning against the cage sides [30]. This may be more likely to occur in singly housed and older animals, because they tend to be less active than their socially housed or younger counterparts [2,34]. Therefore, although hair-pulling, activity, and cage friction were not directly assessed in the present study, they may have been contributors to hair loss, especially in older animals.…”

Comparing options for pair housing rhesus macaques using behavioral welfare measures

“…Among laboratory rhesus macaques ( Macaca mulatta ), about half are housed socially, generally in isosexual pairs; this figure that has changed little in the past decades according to available literature [Baker et al, 2007; Reinhardt, 1994]. It is well established that socially housed rhesus macaques demonstrate well-being that is superior to that of their singly housed counterparts; pair-housed rhesus macaques display more affiliative interactions, physical activity, play, and exploration than singly housed individuals [Baker et al, 2012a; Eaton et al, 1994; Schapiro et al, 1996] and less abnormal, stereotyped, and self-injurious behavior [Baker et al, 2012a; Lutz et al, 2003; Novak, 2003; Schapiro et al, 1996]. Improved welfare as a result of social housing has been demonstrated in both female–female and male–male adult pairs [Baker et al, 2012a; Doyle et al, 2008; Eaton et al, 1994].…”

“…It is well established that socially housed rhesus macaques demonstrate well-being that is superior to that of their singly housed counterparts; pair-housed rhesus macaques display more affiliative interactions, physical activity, play, and exploration than singly housed individuals [Baker et al, 2012a; Eaton et al, 1994; Schapiro et al, 1996] and less abnormal, stereotyped, and self-injurious behavior [Baker et al, 2012a; Lutz et al, 2003; Novak, 2003; Schapiro et al, 1996]. Improved welfare as a result of social housing has been demonstrated in both female–female and male–male adult pairs [Baker et al, 2012a; Doyle et al, 2008; Eaton et al, 1994]. Pair and group housing may buffer stress for rhesus macaques as they are exposed to research events [Gilbert & Baker, 2011], removed from social groups [Gust et al, 1994], or transported to different facilities [Fernström et al, 2008].…”