Laboratory of Theriogenology, Department of Clinical Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo, 060-0818, Japan.
Noboribetsu Bear Park, Noboribetsu, Hokkaido, 059-0515, Japan.
Theriogenology. 2019 Dec;140:164-170. doi: 10.1016/j.theriogenology.2019.08.027. Epub 2019 Aug 23.
Artificial insemination (AI) may be a useful tool in the reproductive management of endangered animals, including bears. To establish an AI program for bears, we investigated follicular dynamics using weekly transrectal ultrasonography in six captive brown bears. Along with ultrasonography, we monitored plasma progesterone (P) and estradiol-17β (E) concentrations. Furthermore, two bears were administered a gonadotropin releasing hormone (GnRH) agonist to induce ovulation on the first day on which the largest follicle reached more than 10.0 mm in diameter. Brown bears showed two patterns of follicular development in the early and late periods of the breeding season. In the early period (May to mid-June), multiple follicular waves were observed; namely, many follicles developed, and the largest follicles grew to less than 6.0 mm in diameter then regressed. In the late period (mid-June to July), one or two follicles grew to greater than 6.0 mm in diameter and developed as dominant follicles. Moreover, the growth rate of the largest follicle in the late period was faster than that in the early period of the breeding season. One bear with a follicle of 13.1 mm ovulated spontaneously, and one bear ovulated when the follicle was 10.2 mm in diameter after GnRH agonist treatment. Plasma E concentrations increased and showed peaks five to seven days before the largest follicles reached their maximum size. Plasma P concentrations increased on the day the corpus luteum could be detected using ultrasonography. This is the first study that showed there are two patterns of follicular development in brown bears. Furthermore, the largest follicle reaching greater than 10.0 mm in diameter could be an indicator of the appearance of ovulatory follicles.
人工授精（AI）可能是濒危动物（包括熊）生殖管理的有用工具。为了为熊建立 AI 计划，我们使用每周直肠超声检查对六头圈养棕熊的卵泡动态进行了研究。除了超声检查外，我们还监测了血浆孕激素（P）和雌二醇-17β（E）浓度。此外，有两只熊接受了促性腺激素释放激素（GnRH）激动剂的治疗，以便在最大卵泡直径超过 10.0 毫米的第一天诱导排卵。棕熊在繁殖季节的早期和晚期表现出两种卵泡发育模式。在早期（5 月至 6 月中旬），观察到多个卵泡波；即，许多卵泡发育，最大卵泡长到小于 6.0 毫米，然后退化。在晚期（6 月中旬至 7 月），一个或两个卵泡长到大于 6.0 毫米并发育成优势卵泡。此外，在繁殖季节的晚期，最大卵泡的生长速度比早期快。一只卵泡为 13.1 毫米的熊自然排卵，一只卵泡为 10.2 毫米的熊在 GnRH 激动剂治疗后排卵。E 浓度在最大卵泡达到最大尺寸前五天到七天增加并达到峰值。P 浓度在超声检查可以检测到黄体的当天增加。这是首次表明棕熊有两种卵泡发育模式的研究。此外，最大卵泡直径超过 10.0 毫米可能是排卵卵泡出现的指标。
