363 EXTENDING THE IN VIVO MATURATION TIME TO PERMIT FLEXIBLE TIMING OF OOCYTE COLLECTION IN SUPERSTIMULATED WOOD BISON (BISON BISON ATHABASCAE)

Abstract

Wood bison are a species threatened by endemic brucellosis and tuberculosis. Reproductive technologies are being developed in an effort to ensure the genetic diversity of wild wood bison, and to prevent disease transmission to healthy bison, livestock, and humans. For the purposes of IVF, recent results revealed that cumulus cell expansion was more extensive in in vivo- v. in vitro-matured cumulus-oocyte complexes (COC), and more oocytes reached maturity after 30 v. 24 h of in vivo maturation following hCG treatment (Cervantes et al. 2013 Reprod. Fert. Develop. 25, 283). An experiment was designed to determine the effects of an additional 4 h of in vivo maturation on follicle development, unwanted ovulation, and COC collection efficiency. Wood bison cows (n = 28) underwent transvaginal ultrasound-guided follicle ablation to induce emergence of a new follicular wave (Day 0 = day of wave emergence, 1 day after ablation) during the non-breeding season. Bison were given FSH diluted in hyaluronan IM on Days 0 (300 mg) and 2 (100 mg), and 2500 IU hCG IM on Day 4. Bison were then assigned randomly to 2 groups (n = 14 per group) in which transvaginal oocyte collection was done at either 30 or 34 h after hCG treatment. The number and size of follicles available for aspiration (i.e. = 5 mm) was compared between groups by Student's t-test. Binomial data (COC collection rate and ovulation rate) were compared by chi-square, and the proportion of cows that ovulated was compared using a Fisher's exact test. Ovulation was defined as the sudden disappearance of follicles ≥10 mm from the hCG treatment to the time of COC collection. The numbers of follicles ≥5 mm and ≥10 mm at the time of COC collection were not different between the 30 and 34 h groups (19.0 ± 1.4 v. 17.4 ± 2.4, and 9.5 ± 1.2 v. 7.7 ± 1.8), nor was the average size of follicles = 5 mm (9.9 ± 0.2 v. 9.8 ± 0.2 mm). The number of follicles aspirated was similar between the 30 and 34 h groups (16.4 ± 1.4 v. 13.4 ± 2.1), but the pre-collection ovulation rate was lower in the 30 h group (12/89 [13.5%] v. 47/147, [32.0%]; P = 0.003), as was the proportion of bison that ovulated (3/14 v. 10/14, P = 0.02). The COC collection rate was lower in the 30 v. 34 h group (64.3% v. 78.2%; P = 0.003), but the total number of COC collected per bison was similar (10.6 ± 1.7 v. 10.5 ± 1.5). Although waiting for 34 h before COC collection resulted in a larger proportion of unwanted ovulations, a greater collection efficiency in the 34 h group resulted in a similar number of COC collected per bison. We conclude that the 30 to 34 h in vivo maturation window provides flexibility for the purposes of oocyte collection and immediate in vitro fertilization in wood bison.

We thank Bioniche Animal Health for providing FSH (Folltropin-V) and hyaluronan (MAP-5), and Merck Animal Health for hCG (Chorulon).