K. Kotzev, S. Sevov, G. I. Kalaydzhiev, D. Abadjieva Institute of Biology and Immunology of Reproduction “Acad. Kiril Bratanov”, Bulgarian Academy of Sciences, blvd. 73 Tsarigradsko Shose Street, 1113, Sofia, Bulgaria Faculty of Agriculture, Trakia University, 6000, Stara