Polymorphism of nucleolar organizer regions in different Ukrainian cattle breeds

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Aim. To study the activity of nucleolar organizer regions (NORs) in different Ukrainian cattle breeds in terms of their apparent activity status in silver stain and possible relation with milk productivity. Methods. Chromosome prepara- tions using lymphocytes from the peripheral blood of 90 cows of different breeds were used in the study. NOR activity was determined by visual evaluation of concentrations of silver precipitation on NORs in individual chromosomes. A 50 % silver nitrate solution was used to stain chromosome preparations. NORs were detected as dark spots on telomeres of the corresponding chromosomes. Results. The cytological analysis of chromosome preparations from lymphocytes of first lactation cows detected NOR polymorphism in Ukrainian Red-and-Motley dairy cattle (URM), Ukrainian Black-and-White dairy breed (UBW), and hybrid cows, obtained by crossing Ukrainian Red-and-Motley dairy breed and Montbeliarde bulls (URM × M). First lactation cows of URM and UBM had higher or the same inci- dence of cells with four (29.8 and 30 %) and five (17.1 and 19.5 %) NORs, while in URM × M cows the incidence of cells with the same number of NORs was almost twice lower; cells with 7 and 8 NORs exceeded a similar index for other investigated breeds almost twice (2.5 against 4.5 % and 2.0 against 4.2 %). The highest level of chromosomal aberrations (CA) was observed in the group of animals with medium number (2 to 3 NORs per cell), and the lowest – in the group with a high number of NORs (from 6 to 7) with a reliable intergroup difference (p < 0.01). NOR activity was the highest in the group of animals of local origin (URM × M) with a milk yield over 7,000 kg in 305 days of the first lactation and the lowest in the UBW cows with a milk yield of 4–5,000 kg during the first lactation. Conclusions. We determined the differences in the activity of nucleolar organizers between the investigated groups of cows of dairy breed. URM × M hybrids reliably (р ≤ 0.05) exceeded dairy UBW cows by this index. No statistically significant different was found between other investigated groups of animals by this trait. Higher dairy productivity was found in the animals with higher frequency of NORs in the chromosomes of metaphase cells. In our opinion, the number of active NORs demonstrates relative variability between their number and the rate of protein synthesis, required to implement the productivity traits of the investigated animals.