Veterinarija ir Zootechnika

Abstract. The subject of this study is a dairy cattle farm with a capacity of 500 Holstein cows. The housing system is a free-stall group system with individual resting stalls. The study included all cows present on the farm as of April 2024 - a total of 425 animals. Based on individual animal records, the age at first calving and the cows’ age as of April 2024 were calculated. The average age at first calving in the studied herd was within the optimal and recommended range – 716,26 days (23,88 months), with a high average first-lactation milk yield of 11495,21 kg. A substantial variation in the age at first calving was observed depending on year of birth and corresponding lactation number. Only 1,18% of the cows calved for the first time before the age of 660 days. The majority of the cows – 90,35% – had their first calving between 22 and 26 months of age. Only 8,47% calved for the first time after 780 days of age. The variation in age at first calving across lactation numbers suggests that insemination of heifers on this farm typically begins after they reach one year of age. The lowest average first-lactation milk yield was recorded in cows that calved before the age of 659 days. In contrast, the highest average first-lactation milk yield was observed in cows that calved for the first time at over 27 months of age – 12025,54 kg.