147 THE DEVELOPMENTAL CHARACTERISTICS OF IN VITRO-PRODUCED CATTLE-WISENT (BOS TAURUS-BISON BONASUS) HYBRID EMBRYOS

Abstract

Interspecies hybrids are important resources for research and agriculture. Therefore, the aim of this study was to evaluate development, quality, and viability of embryos produced in vitro using cattle (Bos taurus) oocytes and European bison (Bison bonasus) epididymal sperm. The epididymes were obtained following a forced slaughter of one bull aged 7 years. The sperm was collected by scraping the inner surface of the epididymes, diluted with the cryopreservation medium, and equilibrated for 4 h at 4°C. Thereafter, sperm aliquots (0.2 mL) were frozen in liquid nitrogen vapor for 5 min and then plunged into liquid nitrogen for storage. Prior to fertilization, frozen semen was thawed in pre-warmed medium for 1 min at 37°C and prepared by the swim-up method. The frozen-thawed ejaculated sperm from the Russian Black Pied bulls was used as a positive control. Slaughterhouse-derived cumulus-oocyte complexes were matured for 24 h in TCM-199 supplemented with 10% FCS, 0.2 mM sodium pyruvate, 10 μg mL⁻¹ porcine FSH, and 10 μg mL⁻¹ ovine LH. Matured oocytes (35–40 oocytes per group) were co-incubated for 18 h with homologous (n = 266 oocytes) or heterologous (n = 292 oocytes) sperm (spermatozoa/mL) in 500 µL of TALP containing 10 μg mL⁻¹ heparin, 20 μM penicillamine, 10 μM hypotaurine, 1 μM epinephrine, and 0.1% minimal essential medium nonessential amino acids. After IVF, the oocytes were cultured in CR1aa medium (Rosenkrans 1994 J. Anim. Sci. 72, 434–437) to the blastocyst stage. All the cultures were performed at 38.5°C and 5% CO₂ in humidified air. At Days 2 and 7 after insemination, the cleavage and blastocyst rates were determined. In addition, a part of obtained blastocysts was fixed with 4% paraformaldehyde, and the total cell number and apoptotic cell ratio were determined by 4’,6-diamidino-2-phenylindole and TUNEL staining. The remaining blastocysts were cultured up to Day 10, and the hatching rates were assessed. The data (3–5 replicates) were analysed by ANOVA. The cleavage rates did not differ among both male species (72.4 and 77.1%). Furthermore, no significant effects of interspecies fertilization on the blastocyst rate or total cell number per blastocyst were found (27.4 ± 1.6% and 77.0 ± 5.7 for cattle embryos and 26.2 ± 1.9% and 83.1 ± 8.9 for cattle-wisent hybrid embryos). On the other hand, the significant differences between homologous and heterologous fertilization were detected in the rate of hatched blastocysts (60.3 ± 5.1 v. 38 ± 2.9, P < 0.05) and apoptotic cell ratio 7.3 ± 0.8 v. 11.6 ± 1.04, P < 0.05). Our findings demonstrate that hybrid embryos produced by IVF of bovine oocytes with the epididymal sperm of European bison can be developed up to advanced blastocyst stages. However, the hybrid embryos have a lower quality and viability than cattle embryos.

Research was supported by the Program of Presidium of the Russian Academy of Science, project no. IV.13.3.