Strategies for oocyte collection and embryo production in free-roaming bison herds.

The study was conducted to test the feasibility of protocols for field collection of cumulus-oocyte complexes (COC) for embryo production (IVP) in wild bison. The study was done with captive wood bison during the anovulatory season. In Experiment 1, the efficiency of transvaginal ultrasound-guided COC collection was compared between bison restrained in a squeeze chute without sedation vs in lateral recumbency after chemical immobilization using a dart gun ( = 8/group). In Experiment 2, a 2 × 2 design was used to examine the effects of superstimulation treatment [single dose of equine chorionic gonodotrophin (eCG) vs multiple doses of follicle stimulating hormone (FSH)] and method of drug administration (manual injection vs field darting) on COC collection and IVP. In Experiment 1, no difference was detected between chute-restrained vs chemically immobilized groups in the time required to complete COC collections, the number of follicles aspirated (11.5 ± 1.9 vs 9.3 ± 1.8;  = 0.4) or the COC recovery rate [COC recovered/follicle aspirated; 58/92 (63%) vs 44/69 (64%);  = 0.9]. In Experiment 2, no differences were detected between superstimulation treatments (eCG vs FSH). The total number of follicles available for aspiration did not differ between manual injection and field darting (23.9 ± 2.7 vs 21.6 ± 1.9;  = 0.4). Compared with the random start unstimulated group, the embryo production rate was higher [18/132 (14%) vs 53/189 (28%);  = 0.04] after wave synchronization and superstimulation. Results suggest that COC collection is equally feasible in a recumbent position after chemical immobilization as those bison restrained in a standing position in a hydraulic chute. Ovarian superstimulation with a single-dose eCG protocol is as effective as a multiple-dose FSH protocol, and field darting is as effective as chute-side administration of superstimulation treatments. The strategies in the present study are ready to be incorporated into field collections in free-roaming bison herds.