Study on milk yield in high-producing Holstein cows and its influencing factors

The aim of the study was to examine the milk productivity of 359 Holstein cows reared in two different farms on the territory of Southern Bulgaria. The lactation period covered the years 2019-2023. Considering the conditions in our country, we can assert that the cows exhibited high milk productivity. The average (LS) milk yield per normal (305-day) lactation was 10840 ± 64.29 kg, with milk fat 3.82 ± 0.05 % and protein content of 3.30 ± 0.06 %. The milk yield per full lactation (354 ± 7.3 milking days) was 12158 ± 210.59 kg, with milk fat 3.81 ± 0.05 and protein content of 3.30 ± 0.06 %. The milk yield per normal lactation was significantly influenced (0.001) by the farm, the year of calving, the lactation number, and the sire (p < 0.01). The temperament of the cows and the season of calving did not significantly influence any of the examined parameters, whether in relation to full or normal lactation. The daughters of 94% of the bulls produced milk yield exceeding 10 000 kg, while 76% of the bulls had daughters with a yield above 11 000 kg. The milk fat content per normal lactation was significantly influenced (p < 0.001) by the lactation number, whereas the protein content (p < 0.05) was affected by the farm and the year of calving. Keywords: Holstein, milk productivity, sire, temperament