DYNAMICS OF THE INFLUENCE OF GENETIC FACTORS ON THE MILK PRODUCTIVITY OF COWS DURING CHANGES IN THE LEVEL OF PRODUCTIVITY IN THE HERD

The research was conducted in the herd of the Khrystynivske Research Farm of the Institute of Animal Breeding and Genetics n.a.M.V. Zubets of the National Academy of Sciences of Ukraine using animals of the Ukrainian Red-and-White Dairy and Holstein breeds, taking into account periods of different levels of productivity in the herd. The milk productivity indicators were analyzed based on the results of three lactations of 1.127 daughters from 13 bulls over 10 years. It was found that under the best conditions of maintenance (2014–2018), the first-born Holstein breed cows had a statistically significant advantage in terms of milk yield over their peers of the Ukrainian Red-and-White Dairy breed. Under less favorable conditions (2019–2022), no statistically significant difference in terms of milk productivity in the groups of half-sisters by father during all lactations was established. With a decrease in milk yield in the herd, the effect of the breed on milk productivity during all lactations is practically absent. The analysis of variance showed that for the entire period under study (2014–2023), the heredity of the father had a statistically significant effect on milk yield – in first-born cows at the level of 18%, in second-lactation cows – 10%, in third-lactation cows – 15%; on the fat content in milk for the first lactation – 4.5%, in the second – 8%, in the third – 13%; on the protein content in milk for first-born cows – 11%, in the second lactation – 6.4%. Differences were found in the level and number of traits that are statistically significantly affected by the heredity of the father during periods with different levels of milk yield in the herd. It should be noted that the effect of the heredity of the father on the age of first calving of daughters was statistically significant in all periods under study. However, during the period of relative decline in cow welfare, this indicator was significantly lower (ɳ2x = 0.064 ± 0.0192, P < 0.001) compared to the best period in terms of milk yield (ɳ2x = 0.42 ± 0.025, P < 0.001) and the entire period (2014–2023) of the study (ɳ2x = 0.42 ± 0.013, P < 0.001).