194 ESTROUS SYNCHRONIZATION AND FIXED-TIME AI IN WOOD BISON (BISON BISON ATHABASCAE)

Abstract

As part of a project involving reproductive biotechnology as a method of preserving Canada’s threatened wood bison population, an experiment was designed to test the effectiveness of steroid-induced ovarian synchronization and fixed-timed AI. The experiment was performed in the early ovulatory season (September) with female wood bison (4 years old, n = 13) and plains bison (2 years old, n = 4, and 8 years old, n = 3). Based on results of a preceding study, progesterone was combined with estradiol as a synchronization treatment to mitigate against untimely ovulation. The bison were blocked by subspecies and assigned randomly to a control group (no treatment; n = 10) or given estradiol 17β (2.5 mg) + progesterone (50 mg) in canola oil i.m. and a progesterone-releasing intravaginal device (Cue-mate™, Bioniche, Belleville, Ontario, Canada) on Day 0 (n = 10). On Day 8, the Cue-mate™ device was removed and PGF (500 mg Estrumate^®, Mallinckrodt Vet GmbH, Friesoythe, Germany) was given to induce luteolysis. On Day 10, all bison were given 5 mg of LH (Lutropin^®-V, Bioniche) and artificially inseminated 12 h later with semen collected and frozen previously from wood bison of the same herd. The ovaries were examined daily by transrectal ultrasonography beginning 5 days before treatment and thereafter until the first post-treatment ovulation. Ultrasonographic pregnancy diagnosis was done 30 days post-insemination. No differences were detected between wood and plains bison for any end point, and data were combined for further statistical analyses. Ovarian follicular wave emergence occurred on Day 4.1 ± 0.8 (mean ± SEM) and 4.1 ± 0.3 in the control and treatment groups, respectively (P = 99.3). The interval to new wave emergence was less variable in bison treated with estradiol + progesterone than in untreated controls (residuals, 0.7 ± 0.2 and 1.9 ± 0.5 days, respectively; P < 0.05). The interval from LH administration to ovulation was 2.7 ± 0.6 and 5.4 ± 1.9 days for the treatment and control groups, respectively, and was less variable in the treatment group than in controls (residuals, 1.2 ± 0.4 and 5.3 ± 0.8 days, respectively; P < 0.05). The diameter of the preovulatory follicle was not different between groups and was, on average, 15.2 ± 1.1 mm. Pregnancy was diagnosed in 3 bison in the treatment group and 2 in the control group. In conclusion, treatment with estradiol and progesterone effectively synchronized the interval to wave emergence, and subsequent LH treatment resulted in a synchronous ovulatory response necessary for fixed-time AI in bison. Although the pregnancy rate was modest, perhaps because of issues with semen quality, timing of AI, or quality of the ovulated oocyte, this represents the first report of pregnancy in bison from fixed-time insemination.

Supported by grants from the Advancing Canadian Agriculture and Agri-Food Fund, the Agri-Food Innovation Fund, Parks Canada, the World Wildlife Fund, and the Northwest Territories.