Eficiência da produção in vitro de embriões de doadoras e touros holândes, Gir e Girolando em diferentes estações do ano

Abstract

The market for in vitro production of bovine embryos (IVP) has expanded in recent years, surpassing even the figures for in vivo production. IVP consists of obtaining oocytes from cows in vivo, by means of the ovum-pick-up (OPU) technique, maturation and fertilization of oocytes, and in vitro culture of putative zygotes, which can be transferred to recipients or cryopreserved. However, many factors can interfere with the success of the technique, whether related to the donor cow, the sire, the environment, or laboratory procedures. This study aims to analyze some factors that may affect the outcomes of IVP in dairy cows. The analyzed database comes from a commercial laboratory and includes information related to 934 IVP routines. The database contained information about the genetic groups of the donor and sires, namely, Holstein (HO), Gir, and 3⁄4 Holstein x Zebu crosses (Girolando), farm, season in which the OPU was performed, and numbers of viable, denuded, and irregular oocytes. Additionally, the numbers of matured, cultivated, cleaved, and total embryos produced were recorded. All OPU sessions, as well as all IVP routines were performed by a single technician, and sex-sorted-semen (female) was used in all routines. Data were analyzed by generalized linear models in SAS® software (OnDmand for Academics, v.9.4) and a significant effect was assumed when P < 0.05. The total numbers of oocytes were 12.57 ± 0.76, 18.11 ± 1.23, and 20.85 ± 1.58 from HO, Gir, and Girolando donors, respectively. HO donors produced fewer (P < 0.05) viable oocytes than Gir and Girolando donors. HO donors produced more (P < 0.05) viable oocytes in the winter (5.18 ± 0.47) than in the spring (3.96 ± 0.40), summer (4.94 ± 0.57), and autumn (4.18 ± 0.46) seasons; however, season did not influence (P > 0.05) the number of viable oocytes from Gir and Girolando donors (interactive effect between donor breed and season, P < 0.05). Sire genetic group within donor genetic group x season combination influenced the cleavage rate (CR, P < 0.05) and the production of embryos in relation to the total oocytes (P < 0.05), and to the cleaved embryos (P < 0.05). The CR of HO x HO embryos did not differ (P > 0.05) between seasons; however, the CR of HO x Gir embryos was higher (P < 0.05) in the spring (58.31 ± 2.95%) than in the winter (45.05 ± 2.54%). The CR of Girolando donors and the embryo production rate of Gir donors in the winter were reduced (P < 0.05) by using semen from sires of the same genetic group as the donors. The cleavage and embryo production rates of HO and Gir donors varied depending on the bull used for fertilization. These findings provide a basis for the development of personalized strategies that maximize the success of the technique and, consequently, improve the reproductive performance and genetic progress in dairy herds.