72 In vitro embryo production using prepubertal calf oocytes with conventional semen and sexed semen ULTRA-4M

In vitro embryo production (IVP) can increase the reproductive potential and genetic quality of cattle, as well as other species. This powerful assisted reproduction tool can be used to produce embryos from prepubertal calves, reducing the generation interval. A recent sexed semen technology known as ULTRA (ST Genetics), completely modified the technique, the media and sperm concentration. In field trials with AI there was no difference between conventional semen (CONV) and ultra-sexed semen at a concentration of 4 million per straw (ULTRA-4M). The combined use of IVP and ULTRA-4M can decrease the selection time for improving dairy and beef cattle herd genetics. The objective of this research was to compare the CONV and ULTRA-4M semen using bovine IVP and prepubertal calves. The research was carried out in the reproduction laboratory of the Facultad de Estudios Superiores Cuautitlan - Universidad Nacional Autonoma de Mexico (FESC-UNAM). The IVP was performed with a continuous in vitro culture (IVC) system. The ovaries were collected in Campeche, Mexico, from Bos indicus × Bos taurus crossbred calves (6 months old) using surgical castration (for export to the United States) and transported to the laboratory (FESC-UNAM) in BO-HEPES-IVM (Bioscience™), in an oocyte transporter (WTA). Vitrogen media were used for IVF and IVC. For IVM, the cumulus-oocyte complexes (COCs) were selected (only grades 1 and 2) and matured for 24 h at 38.5°C. Matured oocytes (n = 600, divided equally into five replicates) were divided into 2 groups, the CONV group and the ULTRA-4M group. The IVF process was conducted with CONV and ULTRA-4M semen from the same bull (Holstein) at a concentration of 2 × 106 and 0.5 × 106 spermatozoa mL−1, respectively, for 18 h in 38.5°C, 5% CO2, 95% air, and 100% humidity. The presumptive zygotes were denuded by pipetting and set in IVC until Day 7 at 38.5°C, 5% CO2, 5% O2, and 90% N2 at 100% humidity. The cleavage results were recorded 56 h after the beginning of IVC. The cleavage rate, embryos with more than 6 cells, and blastocysts on Day 7 of culture were evaluated. The statistical analysis was carried out with the GLM procedure of the SAS software (version 9.3; SAS Institute Inc.) to evaluate the results of CONV vs. ULTRA-4M (α level = 0.05). The percentage of cleavage for CONV was 46% ± 1.4 and 43.2% ± 1.4 for ULTRA-4M. The results for embryos with more than 6 cells in the CONV and ULTRA-4M groups were 16% ± 0.6 and 14% ± 0.6, respectively. The percentage of blastocysts on Day 7 for CONV was 9% ± 0.6 and 8% ± 0.6 for ULTRA-4M. There were no significant differences between groups (P > 0.05) for all variables analysed. In conclusion, under the conditions of this research the ULTRA-4M and CONV produced similar results for IVP.