Investigation of the effect of cow estrous serum when added to the maturation medium of oocyte-cumulus complexes IN VITRO

Saving and multiplying the existing livestock population is an important strategic objective that ensures the country's food security and levelling the dependence on imports of genetically valuable highly productive animals. Obtaining farm animal embryos in vitro is one of the methods of assisted reproductive technologies (ART), which can be used both lifetime and post-mortem. This method allows to optimise breeding work with livestock in a short period of time due to the large number of offspring obtained from highly productive individuals. Aim and objectives: to investigate the effect of bovine estrous serum on meiotic oocyte maturation and early embryogenesis prior to blastocyst development, when added to oocyte-cumulus complexes (OCC) maturation medium. A blind randomised controlled trial was conducted on the effect of bovine estral serum on blastocyst development when added to OCC maturation medium. Estral serum was obtained from the blood of clinically healthy cows with pronounced signs of puberty. The study was carried out in conditions of industrial livestock breeding. The material for the study were oocyte-cumulus complexes obtained by the method of lifetime aspiration from 89 Holstein cows with milk productivity of more than 10 thousand kg per lactation. Oocyte-cumulus complexes were divided into 2 groups: Group 1 (control) - oocyte maturation was carried out in commercial IVM medium without addition of estrous serum, Group 2 (experiment) - oocyte maturation was carried out in commercial IVM medium with addition of es trous serum in concentration from 5 to 15%. The hormones, growth factors and biologically active substances contained in estrous serum have no effect on the achievement of OCC at the stage of metaphase II of meiosis, as well as at the stage of fractions; moreover, a negative effect at these stages of development can be traced. However, substances contained in estrous serum are able to saturate and accumulate in OCC at the stage of maturation to metaphase II of meiosis, thus enhancing the potential of oocytes to embryonic development and further positively affect their achievement of the blastocyst stage. The difference in the formation of blastocysts from crushed embryos reaches more than 25%, and the difference in the formation of blastocysts from viable JCCs matured in media without serum and modified with estrous serum is 37.5% in favour of the latter.