Cytogenetic status of mares (Equus caballus) of Ukrainian riding breed influences their fertility

Cytogenetic studies of mares are widely used in practice (in case of embryonic death this is a mandatory test) in countries with developed horse breeding. Genetic evaluation of Equus caballus is also widely performed. Nevertheless, in the available literature, we could not find publications on the relationship between cytogenetic disorders in mares and the effectiveness of artificial insemination with frozen and thawed sperm. This paper is the first report on the impact of the cytogenetic status of mares E. caballus of Ukrainian horse breed on their sexual cycle and the efficacy of the artificial insemination by Kharkov technology. It has been shown that in case of ovary hypofunction caused by an increased chromosomal variability, as estimated by the per cent of aberrant metaphases with no genome mutations and the transmitted cytogenetic disturbances found, it is necessary to divide the mares into three groups: up to 5 %, from 5 to 10 % and over 10 % overall chromosomal instability. This allows better characterization of mares' physiological condition to optimized treatment and the artificial insemination procedure by Kharkov technology. When cooled semen used, the fertility of the mares having more than 10 % aberrant metaphases was the lowest, by 29.81 and 31.86 % less (р 0.01) compared to mares from the groups with lower chromosomal instability. When thawed semen was used, the fertility was the highest in the mares with the chromosomal instability up to 5 %, that is, on average 14.93 % higher (р 0.05) compared to the mares with more than 5 % of metaphases with aberrations. The influence of cytogenetic status on the fertility in the insemination was clearly seen when the cryopreserved semen was used as compared to cooled semen. The fertility of the mares inseminated with cryopreserved sperm averaged was 71.60 % in group 1 (up to 5 % aberrant metaphases), 56.67 % in group 2 (5-10 % aberrant metaphases), and only 37.04 % in group 3 ( 10 % aberrant metaphases). So, estimation of cytogenetic status ensures optimization of artificial insemination and an increase in mares' fertility when used cooled and frozen-thawed semen.