310 DOES PROGESTERONE OR EQUINE CHORIONIC GONADOTROPIN IMPROVE THE SUPEROVULATORY RESPONSE AND EMBRYO QUALITY IN WOOD BISON DURING THE ANOVULATORY SEASON?

Abstract

Superovulation protocols are being developed in wood bison (Bison bison athabascae), a threatened Canadian species. In initial studies, 2 doses of FSH diluted in hyaluronan given 48 h apart were successful for inducing ovarian superstimulation in wood bison, and ovulation rate was improved by final treatment with hCG instead of LH (Palomino et al. 2012 Reprod. Fertil. Dev. 24, 226). In that study, exogenous progesterone had no effect on the number of ovulations, but embryo quality could not be evaluated because of the low number of embryos collected. In beef cattle, replacement of the final doses of FSH with eCG has resulted in the recovery of a greater number of ova/embryos. The objective of the present study was to evaluate the effect of exogenous progesterone (PRID) on embryo quality and to determine if the addition of eCG increases the ovulation rate in superstimulated wood bison. Follicular ablation was done to synchronize follicular wave emergence in 26 wood bison cows during the anovulatory season (May). Cows were assigned randomly to 3 groups: PRID/no eCG (n = 8), PRID/eCG (n = 9), and no PRID/eCG (n = 9). A PRID was inserted on the day of follicular ablation (Day –1) in respective groups. In all bison, FSH diluted in hyaluronan (5 mg mL^–1, MAP-5, Bioniche Animal Health Inc., Belleville, Ontario, Canada) was given intramuscularly on Day 0 (300 mg) and Day 2 (100 mg). On Day 3, a single dose of 450 IU of eCG (Pregnecol, Bioniche Animal Health Inc.) was given intramuscularly and the PRID were removed in the corresponding groups. On Day 5, all bison were given 2500 IU of hCG (Chorulon, Merck, Whitehouse Station, NJ, USA) intramuscularly to induce ovulation. Bison were inseminated with chilled semen 12 and 24 h later. Nonsurgical embryo collection was performed on Day 14. Transrectal ultrasonography was done to record the ovarian response, ovulation rate, and number of corpora lutea (CL). Results were compared by ANOVA and Chi-squared test (Table 1). The number of ovulatory-sized follicles (≥9 mm) on Day 5 did not differ among groups. Ovulation rate was lowest in bison treated with both a PRID and eCG (P < 0.05). There were no differences among groups in the number of CL on Day 14, the number of ova/embryos collected, or the number of transferable embryos. The superovulatory response and embryo collection rate in the present study were higher than in any previous reports in bison. The ovulation rate was not improved by the addition of eCG treatment, and exogenous progesterone had no effect on embryo quality.

Table 1.  Response of superstimulated wood bison (mean ± SEM) to treatment with exogenous progesterone (PRID) and/or eCG