mise à jour du
28 octobre 2006
J American Association for Laboratory Animal Science
2006; 45(5):35-43
Effects of Outdoor Housing on Self-Injurious
and Stereotypic Behavior
in Adult Male Rhesus Macaques (Macaca mulatta)
M Babette Fontenot, Mandi N Wilkes, and Cheryl S Lynch
Psychology Department
new iberia research center, behavioral sciences University of louisiana at lafayette,


Abstract: We examined the effects of outdoor housing on self-injurious and stereotypic behavior in adult male rhesus macaques with a history of self-wounding that were previously singly housed indoors for at least 4 y prior to the study.
Baseline behavioral observations were collected over 2.5 mo. In phase 1, animals were relocated outdoors in 1 of 2 experimental conditions, grouphoused (n =8) or single-housed (n =5), for 6 wk. In phase 2, group-housed animals were observed outdoors for an additional 6 wk.
Behavioral observations were done using focal sampling techniques. In phase 1, rates of self-biting and self-directed stereotypies and time spent displaying idiosyncratic self-directed stereotypies decreased significantly when group- and single-housed animals were housed outdoors. Rates of yawning and scratching were significantly decreased for group- and single-housed animals and, for group-housed animals, self-grooming decreased with outdoor housing.
In phase 2, rates of self-biting, time engaging in idiosyncratic self-directed stereotypies, and yawning remained significantly lower during weeks 7 through 12 (outdoor housing) compared with those under indoor housing. Rates of scratching and time spent self-grooming decreased significantly during the first 6 wk but then returned to baseline levels.
Our findings suggest that self-biting and self-directed stereotypic behavior in rhesus macaques with a history of self-injurious behavior is significantly reduced by outdoor housing regardless of whether animals are socially or individually housed.
In rhesus macaques, prolonged individual housing, particularly if initiated at an early age, is implicated as a leading contributing factor to the development of self-injurious behavior (SIB). Therefore, several studies have examined the effects of socially housing animals that exhibit SIB. Mitchell13 attempted to pair juvenile social isolates with adults, age-mates, or infants in a playroom for 15-min intervals, but he found that exposing juveniles to adults or age-mates did not significantly reduce SIB.
However, the exposure was probably too brief to realistically evaluate any positive effects of socialization on these animals.Bayne, Dexter, and Suomi2 compared animals that were housed individually indoors with those that were housed in outdoor groups in either runs or corncribs and found that animals housed socially in corncribs exhibited significantly lower rates of SIB than those among monkeys housed individually indoors.
Reinhardt15 showed that in 7 rhesus monkeys paired with samesex partners, rates of SIB decreased immediately in 3 animals, whereas they diminished gradually over a 2-mo period in the remaining 4 animals. Finally, Weed and colleagues21 paired vasectomized monkeys with females and found that instances of SIB were "markedly reduced" in the males.
Overall, these studies suggest that social housing may have ameliorative effects on rates of SIB. However, it is unclear whether housing animals in an outdoor environment contributes to the effects of group housing. Therefore, we investigated whether housing animals outdoors reduces rates of SIB and amount of time displaying stereotypic behavior more than does group-housing alone.
In phase 1, we found that when housed outdoors, regardless of social housing, animals displayed significantly (P < 0.05) lower rates of biting and self-directed stereotypic behavior and spent significantly (P < 0.05) less time displaying idiosyncratic self-directed behavior. Group-housed animals spent less time pacing. However we had no evidence that outdoor housing had an effect on self-wounding. In phase 2, we found that rates of biting, percentage of total time spent displaying idiosyncratic self-directed stereotypies, stereotypic body movement, and pacing decreased over 12 wk of outdoor
housing. Again, we found no evidence that self-wounding was decreased in group-housed animals over the 12-wk period.
In phase 1, rates of yawning and scratching and percentages of total time spent manipulating toys and in neutral behavior decreased and the amount of time spent resting increased when animals were housed outdoors. For animals housed in grooutdoors, the amounts of time spent pacing and self-groomingdecreased whereas the percentage of total time spent locomoting and scanning increased.
In phase 2, group-housed animals spent more time scanning, resting, and locomoting and less time manipulating toys when housed outdoors throughout the 12-wk period. Rates of yawning outdoors remained lower than indoor levels. However, percentages of total time spent self-grooming and in neutral behaviors as well as the rate of scratching returned to baseline levels.
The absence of effects of housing on self-wounding could be related to our relatively small sample size combined with observations that self-wounding occurs only rarely and sporadically among animals that self-bite. Lutz and colleagues11found that although 25% of the 362 monkeys they examined engaged in self-biting, only 11% had a veterinarian record of SIB. Although we found evidence that stereotypic behaviors and self-biting were decreased in the present study, further research is required to determine the effects, if any, of outdoor housing on self-wounding.
One possible explanation for the reduction in self-biting and self-directed and other stereotypic behavior is suggested from the results of Novak,14 who found that SIB could be elicited by exposure to stressful procedures such as husbandry routines or veterinary procedures. At our facility, outdoor housing provides  more space for animals to avoid close contact with care staff, and husbandry routines are less labor intensive. In addition, veterinary procedures typically are not done outdoors. Insofar as yawning, scratching (phase 1), self-grooming (phase 1), and self-directed behavior reflect levels of anxiety,1,3,16,17,20 decrease in these behaviors suggests that outdoor housing was less stressful during the first 6 wk. Among group-housed animals in weeks 7 through 12 of phase 2, scratching and self-grooming returned to baseline levels and may reflect increased tension among or between the social groups.
In our study, outdoor housing provided a 114% increase in floor area for single-housed animals and a 364% to 837% increase in floor area for group-housed animals; these increases could have contributed to changes in physical activity. Although previous research found that reductions in cage size to 20% of that specified by US Department of Agriculture regulations led to decreased locomotion, increasing cage area to 148% of the mandated size had no effect on either abnormal or normal behaviors of pigtailed macaques (M. nemestrina). Similarly, in long-tailed (M. fascicularis) and rhesus macaques, increasing cage size did not have an effect on abnormal behavior or activity level. It should be noted that all of these studies compared cage size effects on behavior in an indoor environment. We found that group-housed animals, which received the largest increase in cage area, had significant increases in locomotionand scanning and decreased pacing, whereas these behaviors did not change significantly in single-housed animals. These results may have been influenced by increased cage space. A follow-up study examining outdoor housing in cages equivalent in dimension to indoor cages is required to adequately differentiate the potential effects of changes in cage area from outdoor housing on behavior.
In addition to increased space, outdoor housing exposes animalsto natural perceptual stimuli such as sunlight, dusk-dawntransition, natural sounds, and temperature variation. Ourobservations were done during the winter months (November through February) when temperatures averaged 14.8 C (range, 0 to 27.8 C), whereas indoor temperatures were relatively constant (range, 22.2 to 26.7 C). Macaques may budget their activity in order to save energy when environmental temperatures are relatively low. Therefore relatively cold environmental temperatures may promote increases in energy-conserving activities such as resting, scanning, and locomotion, and decreases in activitie such as pacing. We found that environmental temperature altered scanning in single-housed animals during phase 1 and neutral behaviors in group-housed animals in phase 2. However, we found no evidence that temperature affected SIB, stereotypic, and most of the general behavior examined. Seasonal studies with a larger sample size would be required to fully examine the potential role of environmental temperature.
The results of our study generally support Bayne, Dexter, and Suomi, who found that animals socially housed in corncribs exhibited less abnormal behavior compared to animals housed individually indoors. However, further studies are needed to determine whether the frequency of self-wounding would be decreased by a change from indoor to outdoor housing. Overall, our results suggest that self-biting and self-directed stereotypic behavior in rhesus macaques with a history of SIB is significantly reduced by outdoor housing, regardless of whether animals are socially or individually housed, and that, when possible, such a change in housing improves well-being. As an adjunct to outdoor housing or when outdoor housing is not possible, pharmacological treatment may be necessary.

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