Evaluation of the effect of Holstein bulls breeding value on cows’ milk productivity of Ukrainian Black-and-White dairy breed

An analysis of the effect of the breeding value (BV) of breeding bulls on the milk productivity indicators of daughter cows for the first, second, third and higher lactations was conducted in the conditions of the breeding reproducer AF “Zoria” of the Lutsk district of the Volyn region. The data was the material for the investigation on zootechnical and breeding registration of cows, borrowed from the electronic information base DFMS “Intesel Orsek” as of August 2024. The BV of sires was determined by the breeding index (ВI), taken from the catalog of bulls recommended for reproduction of the breeding stock in 2024. Based on the BI of the father (sire) from the general totality (n = 270), experimental groups of half-sibling cows were formed: the first (I) group – off spring  of bulls with a low BI (from +485 to +792), the second (II) group – with an average BI (from +912 to +1224) and the third (III) group – with a high BI (from +1490 to +2050). The probability of an intergroup difference was determined using the Student's t-test, and the effect of organized factors (“father” and “father's BV for BI”) was determined using a one-way analysis of variance. It was found that the highest level of milk productivity by quantitative characteristics (yield, amount of milk fat and milk protein) for the first, second and higher lactations was observed in the offspring of bull-sires of group III. However, for the third lactation this trend was not confirmed due to the premature loss of highly productive cows after the first and second lactations, i.e. cows with less high genetic potential remained in group III. Qualitative indicators (fat and protein content in milk) had a statistically significant relationship with the BV of bull-sires only in some cases. Analysis of the coefficients of variability revealed a clear trend of increasing signs of milk productivity of animals (except for the third lactation) with a simultaneous decrease in their variability. It is not possible to claim a close relationship between the milk productivity of daughters and the father's BI based on this search, since the intergroup difference (the advantage in productivity of the offspring of high-ranking sires over the daughters of bulls with lower BI) was not always statistically significant. Thus, according to quantitative characteristics, the difference was significant (P ≤ 0.05–0.001) only between groups I & III – for the first lactation, as well as between groups I & III and II & III – both for the second and higher lactations. The most significant effect of the factor “father's BV for BI” on the milk productivity of daughters was set up in the second lactation (4.81–10.04 %; P ≤ 0.05–0.001 for various characteristics). In the third lactation, the effect of the investigated factor was not statistically confirmed. The maximum values of the effect of the factor “father (total effect)” on the milk productivity of daughter cows were also recorded for the second lactation (8.21–20.20 %; P ≤ 0.05–0.001), the minimum values were recorded for the first (6.64–10.81 %; P ≤ 0.05–0.001). Heritability coefficients (h2) signs of milk productivity, depending on lactation and indicator, varied from 0.037 to 0.760, and their values significantly depended on the indicators of the degree of effect of the investigated factors. It is also important to consider the effect of other genetic and exogenous factors, as well as the specifics of BV evaluation, which could hypothetically affect the results of the search and requires further learning.