Reproductive performance of rhesus macaques (Macaca mulatta) in two outdoor housing conditions.

This study examined the reproductive performance of rhesus macaques maintained in two different housing conditions: high-density semi-sheltered gang cages and low-density outdoor corrals. Two hundred sixteen subjects were housed in 49 gang cages, each of which contained one breeding male and between one and eight breeding females. Two hundred seven subjects were housed in 13 corrals, each of which contained between two and four breeding males and between 9 and 26 breeding females. Over a 3-year period, pregnancy, live birth, and production rates were significantly greater for females in corrals than for females in gang cages. Fetal death rate was lower in corrals than in gang cages, while neonatal death rates did not differ between housing conditions. These differences did not result from potential confounds such as differential age structures or virological statuses between housing conditions. We conclude that, for rhesus macaques, outdoor corral housing leads to better reproductive performance than does semi-sheltered gang housing, probably as a result of increased individual space and relaxation of intense social stressors.