VARIABILITY OF CYTOGENETIC PARAMETERS IN BLACK-AND-WHITE AND REDAND-WHITE HOLSTEIN BULLS

Carriers of chromosomal aberrations that do not exhibit phenotypic or behavioral effects may be included in the breeding process, resulting in significant economic losses due to veterinary examinations and costs associated with maintaining sterile or infertile sires for many years. Chromosome analysis remains a key screening procedure for chromosomal aberrations in animal cytogenetic laboratories. The aim of the work was to study the variability of the karyotype of cattle sires. Cytogenetic monitoring showed that the modal number of chromosomes corresponded to the species standard and was 2n = 60XY, the fundamental number of the karyotype was (FN = 62), leukocyte chimerism (60XX/60XY) was absent. Constitutional anomalies in the form of Robertsonian translocations were not detected. The average frequency of genomic disorders (aneuploidies) in the studied Holstein Red-and-White bulls was 1.6 ± 0.36% and Holstein Black-and-White bulls – 1.4 ± 0.22% and did not exceed the indicators characteristic of the species. A multiple increase in chromosomes (polyploidy) was not detected. Structural disorders (chromosome breaks) were 2.0 ± 0.50% and 2.2 ± 0.38%, respectively. The frequency of asynchronous divergence of centromeric regions of chromosomes in Holstein Red-and-White bulls offspring was 1.3 ± 0.47% and 1.8 ± 0.75% in Holstein Black-and-White ones. The proportion of cells with micronuclei was within the spontaneous level typical for mammals kept in the absence of direct genotoxic effects and ranged from 0.5‰ to 3.0‰, the limit of the proportion of binuclear lymphocytes was 2.9–4.0‰ and the proportion of dividing cells (MI) was 2.0–8.0‰. It was established that the studied Holstein Black-and-White and Holstein Red-and-White bulls offspring were characterized by stable cytogenetic indicators of somatic mutagenesis.