INFLUENCE OF GENOTYPIC FACTORS ON MILK PRODUCTIVITY TRAITS IN BROWN SWISS COWS

Abstract. The article presents the results of a study on the influence of genotypic factors (sire lineage, line affiliation) on the development of key milk productivity traits in the first-calf Brown Swiss cows at the dairy production complex LLC “ Yekaterynoslavskyi”. The herd of the Brown Swiss cattle originates from four genealogical lines of the breed: Distinction 159523 – 35%, Elegant 148551.66 – 30%, Stretch 143612 – 24%, and Payven 136140 – 11%. The inclusion of these genealogical lines in the farm is due to the high breeding and productive qualities of their offspring, as well as the presence of a significant number of cows and heifers sired by bulls of these lines in the herd. It was noted that the Brown Swiss cows from different genealogical lines, under identical conditions of housing and feeding, showed significant differences in milk productivity traits. The highest milk yield (9768 ± 127.1 kg) was demonstrated by cows of the Stretch 143612 line, which significantly exceeded their peers from other lines (P < 0,001). At the same time, the descendants of this line had the lowest fat (3.81 ± 0.021%) and protein (3.23 ± 0.012%) contents in milk. It was found that first-calf cows of different origins were characterized by a considerable level of variability in the main milk productivity traits. The daughters of the bull Apex 109736195, who had the lowest milk yield (8048 ± 134.2 kg), turned out to have the best fat and protein content in milk (4.30 and 3.36%, respectively). In contrast, the daughters of the bull Sesdeblum 68144448 had the highest milk yield (10,445 kg) but showed the lowest fat and protein levels (3.77 and 3.08%, respectively). The difference is significant in all cases (P < 0,001). The influence of Brown Swiss sires on milk yield and milk composition in their daughters was as follows: for milk yield over 305 days of lactation: ɳ2х = 0.510 (P = 0.001), indicating a high level of genetic determination; for milk fat content: ɳ2х = 0.03, a statistically insignificant value, indicating minimal heritability; for milk protein content: η² = 0.11 (P < 0.01), indicating a moderate but significant paternal influence. The variability in the main milk productivity traits of first-calf Brown Swiss cows is determined more by the differences between offspring of individual sires within the same genealogical line than by their line affiliation alone.