Effect of maturation period with different oxygen tension and type of semen in cleavage rates, blastocyst yield and pregnancy outcome in Nelore (Bos indicus) cattle

This study aimed to evaluate the incubation conditions established during in vitro maturation (IVM) of oocytes (duration and oxygen tension), the type of semen (conventional (C), n = 12.177; and sexed (S), n = 3.630) and the possible correlations with cleavage, blastocyst and pregnancy rates. Selected COCs were transported in 2 mL cryotubes (1 oocyte /13.3 μL medium) containing 400μL of IVM medium TCM-199 (supplemented with 0.2 mM pyruvate, 10% FCS and gonadotropins) and 300 μL of oil silicone at 38.5°C and atmosphere of 5% CO2, 5% O2 and 90% N2. After the transport period, the cryotubes were transferred to incubator with 100% of humidity at 38.5°C with an atmosphere of 5% CO2 (≅ 20% O2), with a total time ranging from 20-29 h of IVM (24 h in average). The timing of fertilization was set according to the type of semen, i.e.,18 to 20 h for the conventional semen and 8 to 10 h for the sexed-semen. Presumptive zygotes were denuded and cultured in SOFaa supplemented with 2.5% FCS up to 7 days. The cleavage and blastocyst rates were evaluated at 72 and 168 hours postinsemination (hpi), respectively, and the procedures were performed at Embriza Laboratory, Campo Grande, Mato Grosso do Sul, Brazil. Rates of cleavage, blastocyst and pregnancy were analyzed by ANOVA, means were compared by SNK test (P 0.05) with the variables studied. Therefore, it can be concluded that: 1) changing the period of IVM and the gaseous atmosphere in the transport of oocytes had no influence in the blastocyst and pregnancy rates, and this use can be indicated for transportation period and 2) the pregnancy rate was higher when using sexed-semen with a shorter fertilization period.