Abstract
Animal populations primarily have been kept within the limits of food supplies and habitats in wild nature. However, under certain circumstances, uncontrolled increase in population occurs in some species, and have caused social problem. In the case of free-ranging Japanese macaques, provisioning was initiated for research, education of mission, and resource of sightseeing more than 50 years ago. The provisioning, through the nutritious and sufficient amount of food supply, made a rapid increase in populations in most monkey parks. Consequently, monkey parks and adjacent agricultural industry face problems associated with the surplus animals. Though various measures for population control, such as hunting, trapping, and relocation, have been taken, these methods have only transient effects. In the present study, we investigated the effects of synthetic progesterone implant on menstrual cyclicity, endocrinology and contraceptive efficacy. Before treatments, all monkeys exhibited normal menstrual cycles with mid-cycle increase in plasma estradiol and LH, followed by luteal increase in plasma progesterone. After treatments, menstrual cycles completely disappeared and annovulation persisted for 3 years, followed by the spontaneous recovery of normal menstrual cycles. Then, 43 female Japanese macaques of the provisioned free-ranging Takasakiyama troop were used for contraceptive study. They received implants in early autumn, just before the onset of breeding season. These monkeys exhibited copulatory behaviors during the breeding season, but they did not show delivery. These results showed that implant suppressed ovulation. Thus, the implant appears an effective means of fertility control in macaque monkeys.
