Abstract
Because Japanese black bears are regarded as copulatory ovulators, the establishment of an ovulation induction method would facilitate artificial insemination and embryonic transfer in this species. The purpose of this study was to examine the method of ovulation induction by administration of human and/or equine chorionic gonadotropin (hCG and eCG) in Japanese black bears. Nine adult captive females were divided into 3 groups (A, B and C) : Group A, 3 females administered hCG (50 IU/kg, i.m.) in mating season; Group B, 3 females administered eCG (1,000 IU/animal, i.m.), and then hCG (35 IU/kg, i.m.) after approx. 80 hr in mating season; and Group C, 3 females not treated (controls) and isolated from males during mating season. Females in Group A exhibited no elevation of progesterone levels after mating season, which suggests that they did not ovulate. In two of the three females in Group B, relatively small corpora lutea were observed by macroscopical and histological observation of excised ovaries after about a month of hCG treatments, suggesting that they might have ovulated. The other female which did not ovulate had given birth in the current year, and this may be the reason for no sensitivity to exogenous gonadotropins. From observation of excised ovaries in late August, females in Group C possessed no corpus luteum, suggesting that they did not ovulate. In conclusion, sole administration of hCG would not induce ovulation, and administration of both eCG and hCG was supposed to induce ovulation in Japanese black bears.
