311 SUPEROVULATION OF NORTH AMERICAN BISON WITH TWO INJECTIONS OF FOLLICLE-STIMULATING HORMONE

Few studies have examined superovulation of North American Bison. In cattle, ovarian superstimulation is usually achieved with 6 to 8 injections of FSH at half-day intervals. However, handling bison repeatedly stresses the animals, which could adversely affect their reproductive potential, as well as pose a risk of injury to the bison and handlers. To limit the number of times the bison were handled, we tested a two-injection superovulation scheme using sodium hyaluronate (MAP-5, Bioniche Animal Health Inc., Belleville, Ontario, Canada) in the FSH diluent, which serves to slow the absorption of FSH when given IM. We hypothesised that the two-injection superstimulation protocol would result in recovery of more embryos on average than a single-embryo recovery protocol. Although a traditional superovulation scheme with 6 to 8 injections of FSH would have been a better comparison, our goal was to handle the bison minimally. Eight female bison ranging in age from 5 to 11 years were used as embryo donors. For superovulation, females with a corpus luteum (CL) were given 25 mg of prostaglandin F2a (PGF, Lutalyse, Pfizer Animal Health, New York, NY, USA) IM followed by 266 mg of FSH (Folltropin V in MAP-5 diluent, i.m., Bioniche Animal Health Inc.) 12 days later (or 9 days after presumed oestrus 3 days post-PGF). Forty-eight hours after the first FSH injection, 134 mg of FSH IM and 25 mg of PGF IM were given. Two days later females were put in a pen with a bison bull for natural breeding. Seven days after assumed oestrus, embryos were recovered nonsurgically. Although the situation is not clear in bison, there is evidence in cattle that superovulated cycles influence embryo collections in subsequent cycles. Consequently, females were randomly assigned to a superovulation or single-embryo recovery treatment for each cycle; however, consecutive superovulation protocols were never conducted without a short oestrous cycle in between. Superovulated females were given PGF at embryo recovery after superovulation, followed by PGF 12 to 14 days later, and bred off the assumed oestrus of the second PGF injection. Embryos were collected from females 4 times (2 superovulation and 2 single embryo cycles, except one bison that was superovulated once). Data were analysed using a one-tailed t-test. Superovulation resulted in greater mean numbers of palpable CL (3.7; P < 0.001), embryos collected (1.8; P < 0.05), and transferable quality embryos (0.8; P < 0.05) compared with the single-embryo recovery protocol (mean palpable CL, 1.0; embryos collected, 0.5; transferable embryos, 0.2). Notably, the bison breeding season is July to September and occasionally animals breed in October; this experiment was conducted in October and November. Thirteen transferable embryos were nonsurgically transferred to recipients; 6 pregnancies were established, but 5 were resorbing by 2 months of gestation; 1 healthy calf was carried to term. Two injections of FSH with a long-acting diluent can be used to increase the number of embryos recovered from bison compared with a single-embryo recovery scheme.

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