KARYOTYPAL VARIABILITY OF UKRAINIAN BROWN DAIRY BREED COWS

Cytogenetic analysis of breeding animals makes it possible to identify animals carrying cytogenetic abnormalities, the rate of spontaneous and induced somatic mutagenesis and the level of general genomic instability of animals. Scientists emphasize that in breeding work it is desirable to use animals whose offspring inherit high productivity and do not carry a genetic burden. 
The main factors that contribute to chromosomal instability are environmental factors, enzyme failure, changes in the system of repair or replication of chromosomes, suppression of immunity. It is important that the methods of breeding farm animals also have an impact on the stability of their karyotype. The appearance of deconsolidation of heredity and destruction of gene adaptive complexes during animal crossing has been established. This also applies to the use of related breeds, but obtained in different environmental conditions. As a result, aneuploidy, polyploidy may occur. It is proved that with the help of cytogenetic methods it is possible to establish new sources of genetic variability and prevent the spread of harmful chromosomal aberrations in animal populations. Such work was carried out on the Ukrainian brown dairy breed, created by crossing the local swan breed and related Swiss breed of American and European selections. That is, a related breed was used in its creation, but it had a difference in the selection system and ecological conditions of detention, which in turn may affect the stability of the karyotype of the new breed. 
The aim of our work was to study the variability of the karyotype of cows of the Ukrainian brown dairy breed. 
Materials and methods. Cytogenetic analysis, which was aimed at establishing the karyotype variability of Ukrainian brown dairy cows, was performed on biological material obtained from animals kept in the breeding plant of the State Enterprise "Research Farm of the Institute of Agriculture of the Northeast NAAS NAAS Sumy region. 15 cows were studied. 
Cytogenetic drugs were obtained from peripheral blood lymphocytes taken from the jugular vein using standard techniques. 
RPMI-1640 medium, bovine serum (preferably embryonic), antibiotic gentamicin, mitogen, a substance that stimulates mitotic division of lymphocytes in culture (phytohemagglutinin type P), were used to cultivate blood cells. The mixture was cultured in a thermostat at +37°C for 48 hours. Two hours before fixation, a solution of colchicine heated to 37°C at a final concentration of 0.3–0.5 μg/ml of culture medium was introduced into the culture. Freshly prepared 0.55% potassium chloride solution was used for hypotension. After hypotension, the culture was centrifuged, the supernatant was drained, and cooled to +4°C fixing fluid was added to the precipitate by mixing one part glacial acetic acid with three parts methyl (or ethyl) alcohol. The obtained preparations, after staining with the finished Giemsa dye, were analyzed for chromosomal variability under immersion magnification of the microscope by 1000 times and photographed. 100 metaphase plates were analyzed in each animal. The number of dinuclear lymphocytes (DJ), mononuclear lymphocytes with micronuclei (MJ), and mitotic index (MI) were counted on the same drugs. The frequency of DIA, IU, MI was calculated in ppm (number per 1000 cells). 
Analysis of karyotype variability of the studied animals showed the presence of quantitative and structural disorders of chromosomes. Quantitative disorders were detected in the form of aneuploidy, the average of which was 5.7%. Multiple chromosome enlargement (polyploidy) in the studied animals was not detected. The average value of asynchronous divergence of the centromeric regions of chromosomes was 0.5%. The limit of variability of ARCR in the studied cows was 0–5.0%, and structural chromosome abnormalities manifested themselves in the form of chromosomal breaks and amounted to 2.1%. According to the results of the micronucleus test, the proportion of lymphocytes with a micronucleus was 1.9‰, binuclear lymphocytes – 3.9‰, and the value of the mitotic index – 3.5‰. 
A positive relationship has been established between aneuploidy and ARCR, which are considered a prerequisite for chromosome loss; aneuploidy and mitotic index (P < 0.05), binuclear lymphocyte and mitotic index. A negative correlation was found between chromosome breakage and micronucleus lymphocyte. 
In animals of different blood levels according to the Swiss breed, chromosome set disorders in the form of aneuploidy were detected, the average values of which were 6.0 and 5.0%, respectively, which corresponds to the limit of spontaneous chromosomal variability. in the studied cows of brown dairy breed higher positive values were found between lymphocytes with a micronucleus and the duration of the service period and the interbody period. It was found that 43% of cows had stillborn calves during the life of the uterus with quantitative chromosome abnormalities (aneuploidy). In animals with undetected aneuploidy, only 25% of cows had stillborn calves during their lifetime. 
According to the results of cytogenetic testing of cows of the Ukrainian brown dairy breed of different linear affiliation, increased variability of the karyotype of animals of the Stretch line has been established. The results of the micronucleus test of brown dairy cows of different linear affiliation indicate the absence of mutagenic factors. 
Conclusions. Quantitative and structural chromosome disorders are characteristic of Ukrainian brown dairy cows. In animals of conditional blood status of 95% and more of the Swiss breed, the highest percentage of cells with aneuploidy (6.0%), the presence of asynchronous divergence of the centromere regions of chromosomes (0.63%) and chromosomal breaks (2.87%). 
According to the results of the micronucleus test, the cytogenetic parameters of cells (lymphocytes with a micronucleus, dinuclear lymphocytes and mitotic index) are 95% higher in animals of conditional blood status and more in the Swiss breed compared to animals of lower conditional blood status. karyotype (aneuploidy) on the percentage of stillbirth of calves and the proportion of lymphocytes with a micronucleus for the duration of the service and interstitial period. Differentiation of quantitative and structural chromosome disorders in brown dairy cows of different linear affiliation has been established. The fact of detection of chromosomal abnormalities indicates the need to significantly expand the scope of the survey of breeding stock, and especially in the leading breeding farms for the cultivation of Ukrainian brown dairy breed.