Trend in fertility outcomes of dairy cows in north-eastern Poland over the past 20 years.

The aim of the study was to evaluate changes in fertility outcomes in several dairy cow herds over the past 20 years in north-eastern Poland. In calving season 2003-2004, 1215 Polish Black and White x Holstein Friesian from 8 herds were used. The average milk yield was about 5000 kg/cow/year. In calving season 2023-2024, 942 Polish-Black-and-White Holstein Friesian cows from 5 herds were used. The average milk yield was 9200 kg/cow/year. First-service conception rate, number of services per conception, length of inter-calving period and culling rate due to infertility were calculated. The average first-service conception rate decreased from 54.5% to 47.0% and the average number of services per conception increased from 1.8 to 2.2. In 2003-2004, the average length of the inter-calving period was 395.3 ± 53.7 days, while in 2023-2024 it was 407.5 ± 55.5 days. The average culling rate due to infertility increased from 4.6% to 11.7%. Differences in all these fertility parameters between calving seasons were statistically significant (p≤0.05). The study showed that the fertility outcomes of dairy cows in north-eastern Poland decreased significantly as milk yield increased between 2003-2004 and 2023-2024.