321 OVARIAN SUPERSTIMULATION AND OOCYTE COLLECTION IN WOOD BISON, A THREATENED CANADIAN SPECIES

Abstract

The wood bison (Bison bison athabascae) is a threatened species, and recovery is constrained by endemic tuberculosis and brucellosis in wild herds in and around Wood Buffalo National Park, Alberta, Canada. The Committee on the Status of Endangered Wildlife in Canada has recommended the eradication of affected herds and repopulation with healthy bison obtained through the use of reproductive technologies. As part of the conservation effort, the specific objective of this study was to develop an effective ovarian superstimulatory protocol in bison that will permit collection of a large number of oocytes for the ultimate purpose of in vitro embryo production. Ovarian function was synchronized among female wood bison during the ovulatory season (December) by giving a luteolytic dose of prostaglandin followed 8 days later by transvaginal ultrasound-guided follicular ablation. On the day after follicular ablation (expected day of follicular wave emergence, Day 0), bison were assigned randomly to 2 groups (n = 11/group) and given either a single intramuscular dose of 2500 IU of eCG or subcutaneous doses of 200 mg of FSH given on Days 0 and 2. A luteolytic dose of prostaglandin was given on Day 2, and 25 mg of LH was given intramuscularly on Day 4. Cumulus–oocyte complexes (COC) were collected 24 h after LH treatment by transvaginal ultrasound-guided follicle aspiration using an 18 G × 2’ aspiration needle attached to a flexible tubing and a regulated vacuum pump (flow rate, 22 mL min^–1). The COC were classified morphologically from 1 (excellent) to 4 (poor) based on attributes of the ooplasm and the number of surrounding cumulus cells. The number of COC in grade 1 to 3 was combined (i.e. grades acceptable for IVF) for purposes of statistical interpretation. Ovarian response and oocyte quality were compared between groups by t-tests, and COC collection rate was compared by chi-square analysis. The number (mean ± SEM) of follicles ≥5 mm was greater (P < 0.05) in bison treated with FSH than in those treated with eCG (12.2 ± 1.7 v. 5.8 ± 0.5), resulting in a greater number of follicles aspirated (11.2 ± 1.8 v. 5.6 ± 0.5; P < 0.05), more COC collected (7.2 ± 1.4 v. 3.4 ± 0.6; P < 0.05), and more COC of acceptable quality (6.1 ± 1.4 v. 2.5 ± 0.5). The COC collection rate (i.e. number of COC collected per number of follicles aspirated), however, did not differ between FSH- and eCG-treated groups [79/123 (64%) v. 37/62 (60%)]. The results document the successful collection of viable oocytes from superstimulated wood bison via tranvaginal ultrasound-guided follicle aspiration. The number of large follicles, follicles aspirated, and COC collected were more than twice as high in bison treated with FSH than in those treated with eCG.