133 In Vitro Embryo Production from Oocytes Collected from Non-Supertimulated Wood Bison (Bison bison athabascae) Following Maturation In Vitro Using Portable Incubators

Abstract

This study was done to determine the feasibility of in vitro embryo production in wood bison during the anovulatory season, without ovarian superstimulation or follicle wave synchronization, to simulate collection conditions in a wild or field setting. The experiment provided the opportunity to compare embryo development using 2 different maturation media and incubator systems. The cumulus-oocyte complexes (COC) were collected by transvaginal ultrasound-guided follicle aspiration during May from non-superstimulated bison. Compact COC were allocated to 2 groups and matured in standard maturation medium using a portable gassed incubator, or in commercial medium using a portable non-gassed incubator. In the former (Standard), the COC were placed in a round-bottomed tube containing TCM-199 medium with 5% calf serum, 5 μg mL⁻¹ LH, 0.5 μg mL⁻¹ FSH, and 0.05 μg mL⁻¹ gentamicin, and the tube was placed in a portable incubator with 5% CO₂. In the latter (Commercial), COC were placed in a round-bottom tube containing the commercial medium (Boviteq, Saint-Hyacinthe, QC, Canada), and placed in a portable incubator without CO₂. After 24 h of maturation, oocytes were fertilized in vitro (Day 0) in Brackett-Oliphant medium at 38.5°C in a conventional incubator with 5% CO₂ humidified atmosphere. Presumptive zygotes were cultured in CR1aa plus 5% calf serum, at 38.5°C and in 5% CO₂, 5% O₂, and 90% N₂ and high humidity. Cleavage was recorded on Day 3 and embryo development was recorded on Day 7. Cleavage and transferable embryo rates (calculated from the total number of oocytes submitted to IVF) were compared between groups by chi-squared test. No difference in cleavage rates was observed between Standard and Commercial treatment groups [68.1 (32/47) v. 79.2% (57/72), respectively; P = 0.25], nor in morula plus blastocyst rates on Day 7 (36.2 v. 45.8%, respectively; P = 0.39). However, the rate of transferable embryos (grade 1 and grade 2) on Day 7 was higher in the Commercial group (38.9 v. 12.8%; P < 0.01). Of the COC in the Commercial group, a higher number of morula plus blastocyst were observed to be compact good COC (>3 layers of cumulus cells) than compact regular COC (1-3 layers of cumulus cells) (66.7 v. 31.0% respectively; P < 0.05), along with a higher number of transferable embryos on Day 7 (60.0 v. 23.8%, respectively; P < 0.05). In conclusion, wood bison oocytes collected during the anovulatory season from non-superstimulated, non-synchronized bison and matured in vitro using portable incubators were competent to develop to the morula and blastocyst stages following IVF and culture. These results are important for future plans that require transporting oocytes from remote collection sites to the IVF laboratory, particularly with respect to the effectiveness of commercial maturation media which does not require CO₂ supplementation.

Research was supported by the Natural Sciences and Engineering Research Council of Canada.