Developing the ovum pick-up technology in cattle: state-of-the-art and research directions (review)

Embryo transfer is an effective method of genetic improvement of cattle, which has become widespread around the world (C. Smith, 1988; N.A. Zinovieva et al., 2020). In 2015, the production of in vitro embryos (IVP-embryos) for the first time exceeded the number of embryos obtained by traditional MOET technology (IVD-embryos), after which it continued to grow, reaching 79.7 % of the total amount of embryos produced in 2021 (J.H.M. Viana, 2022). To date, 98.6 % of IVP embryos are obtained from oocytes retrieved by Ovum Pick-Up (OPU) (R.Yu. Chinarov et al., 2023). In this regard, it is of particular interest to increase the efficiency of OPU/IVP in terms of the quantitative and qualitative characteristics of the retrieved cumulus-oocyte complexes (COCs) (L.B. Ferré et al., 2023). To improve the efficiency of OPU, various approaches are used: optimization of the technical parameters of OPU; conducting OPU at a certain stage of follicular growth and development; increasing the number of simultaneously growing and maturing follicles through the use of gonadotropins; the use of biomarkers and DNA-markers for the selection of donor cows. The aim of this review is to define the factors and approaches affecting the quantitative and qualitative parameters of COCs obtained by OPU, to determine the directions and methodological approaches for further improvement of OPU/IVP technology. Studies of technical parameters have shown the impact on the OPU efficiency of such parameters as the diameter of the aspiration needle and the value of vacuum pressure (V.K. Pestis et al., 2016; F.A. Ward et al., 2000; R.Yu. Chinarov et al., 2022), while the optimal values of the above parameters depend on the type of equipment used and the specifics of the procedure performed by the operator. It was found that the OPU efficiency can be increased when performing oocyte retrieval immediately after the occurrence of the follicular wave before the selection of the dominant follicle (O.J. Ginther et al., 1996), while the developmental competence of oocytes are tended to increase with an increase of follicles size (L.J. Hagemann et al., 1999). Nevertheless, according to some authors, the quality of oocytes does not depend on the size of the follicles, and mainly determined by the follicular phase of the donor (M.M. Seneda et al., 2001). The technological approaches used to bring donor cows to the desired stage of the estrus cycle are conducting the OPU with a certain interval between sessions, the dominant follicle removal and the hormonal synchronization of the estrus cycle (M. Qi et al., 2013). An effective method of increasing the OPU efficiency is to stimulate the simultaneous growth and development of a larger number of follicles through the use of exogenous gonadotropins, e.g,, follicle-stimulating hormone (FSH) and equine chorionic gonadotropin (eCG) (G.A. Bó et al., 2014; L.B. Ferré et al., 2023), while the use of FSH, in most cases, is more effective (F. Rivera et al., 2011; F.L. Ongaratto et al., 2015; G.N. Singina et al., 2019). A promising approach to improve the OPU efficiency is the use of biomarkers (G. Mazzoni et al., 2017; S. Umer et al., 2019; R. Kowsar et al., 2021). Thus, transvaginal ultrasound-guided oocyte retrieval (OPU) is today the main source of oocytes for commercial production of cows’ embryos worldwide, which leads to a wide range of studies aimed at improving the OPU efficiency. Despite the significant progress achieved in the development of OPU/IVP technology, it is necessary to conduct further research in determining the optimal technical and technological parameters of the procedure taking into account the genetic features of various cattle breeds.