415 INDUCTION OF FOLLICULAR WAVE EMERGENCE IN WOOD BISON BY FOLLICULAR ABLATION OR TREATMENT WITH ESTRADIOL AND PROGESTERONE

Abstract

Reclamation of Canada’s threatened wood bison (Bison bison athabascae) herd is complicated by endemic disease. As part of an overall goal to conserve bison genetics, the specific objective of this study was to develop a protocol to control follicular wave emergence in bison for the purposes of ovarian superstimulation and collection of disease-free oocytes. In an initial study, the synchronizing effect of follicular ablation and estradiol (E2) treatment was examined. Ablation was effective, but the effects of E2 (5 mg) were confounded by treatment-induced ovulation in some animals. Two experiments were done to determine the effect of a reduced dose of E2 or the addition of progesterone (P4) in comparison with follicular ablation. Bison cows (n = 19), ≥3 years old, were scanned for 14 days to determine the mean and variance in the interval to follicular wave emergence (control phase). In Experiment 1, bison were assigned randomly to 2 groups: follicular ablation (n = 9) or 2 mg of E2i.m. (n = 10). In Experiment 2, the same bison were randomly assigned to 2 groups: follicular ablation (n = 9) or 2 mg of E2+ 100 mg of P4 i.m. (n = 10). Ablation involved transvaginal ultrasound-guided aspiration of all follicles ≥5 mm. Wave emergence was determined retrospectively by identification of the follicle destined to become dominant at an initial diameter of 4 to 5 mm, with a concurrent increase in the number of follicles ≥4 mm. The interval and variation in the interval to emergence of a new follicular wave was compared among the control phase and treatment groups by ANOVA. In Experiment 1, the interval to new wave emergence (mean ± SEM) was 4.9 ± 0.66, 1.1 ± 0.11, and 2.4 ± 0.47 days from the start of the control phase, follicular ablation, and E2 treatment, respectively (P < 0.001). The degree of synchrony (residuals) was 2.4 ± 0.36, 0.2 ± 0.09, and 1.2 ± 0.24 days for the control phase, follicular ablation, and E2 treatment, respectively (P < 0.001). Ovulation was detected in 1 bison treated with E2. In Experiment 2, the interval to new wave emergence (mean ± SEM) was 4.9 ± 0.66, 1.2 ± 0.15, and 2.9 ± 0.31 days from the start of the control phase, follicular ablation, and E2 + P4 treatment, respectively (P < 0.001). The degree of synchrony was 2.4 ± 0.36, 0.2 ± 0.08, and 0.7 ± 0.20 days for the control phase, follicular ablation, and E2 + P4 treatment, respectively (P < 0.001), and no ovulations were detected. In conclusion, follicular ablation, E2, and E2 + P4 treatments all shortened and decreased the variability in the interval to new wave emergence in bison, but follicular ablation consistently produced a quicker and more synchronous response.

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