Superstimulatory response and oocyte collection in North American bison during the non-breeding season

A 2 × 2 design was used to compare the ovarian response and oocyte collection characteristics in bison given a superstimulatory dose of eCG or FSH, with or without a follow-up dose of LH. Follicular wave emergence was synchronized by follicle ablation (Day −1) and bison were assigned randomly to two superstimulatory treatment groups (n = 10 per group): (i) a single intramuscular dose of 2500 IU of eCG given on Day 0, or (ii) two subcutaneous doses of 200 mg of FSH given on Days 0 and 2. On Day 4, 200 mg of LH was given intramuscularly in 5 bison in each superstimulatory treatment group. The study was done in two replicates (n = 20 per replicate) involving a crossover design so that each animal was given the opposite superstimulatory treatment (eCG or FSH) during successive replicates. Cumulus-oocyte complexes (COC) were collected by transvaginal ultrasound-guided follicle aspiration, and were classified according to morphologic attributes as compact, expanded, or denuded. Superstimulatory treatment with FSH (vs. eCG) resulted in the development of more follicles ≥5 mm (14.2 ± 1.41 vs. 8.2 ± 0.67; P < 0.05; mean ± SEM), and more follicles aspirated (12.4 ± 1.3 vs. 6.3 ± 0.6; P < 0.04). Follow-up treatment with LH (vs. no LH) resulted in a greater proportion of expanded COC (37% vs. 15%; P < 0.05), and a tendency for a higher COC collection rate (61% vs. 54%; P = 0.08). In summary, superstimulation with FSH (vs. eCG) resulted in twice as many follicles available for aspiration and nearly twice as many COC collected in bison during the anovulatory season, and follow-up treatment with LH increased the proportion of expanded COC collected.