Evaluating Lactation Persistency, Lactation Curve Parameters, and Dairy Efficiency: The Role of Parity, Calving Season, and Days Open in Holstein-Friesian Cows

This study investigates the influence of parity, calving season (CS), and days open (DO) on milk yield and lactation traits in Holstein-Friesian cows. A total of 5171 test-day milk yield records collected from 307 cows were analyzed using the Wood equation with non-linear regression. The findings reveal significant effects of these factors on 305-day milk yield (305-dMY), lactation curve parameters (a, b, c), peak milk yield (Y _max ), time to peak yield (T _max ), and lactation persistency (S). Multiparous cows and those calving in winter produced notably higher 305-dMY compared to primiparous cows and cows calving in other seasons. While primiparous cows demonstrated lower initial and peak milk yields and took longer to reach peak yield, they exhibited stronger lactation persistency. Seasonal variations also impacted lactation performance, with autumn and winter calving associated with higher peak milk yield (Y _max ) and improved persistency. Days open (DO) played a crucial role in shaping lactation traits, as cows with 151–180 days open achieved the highest peak yield and lactation persistency, while those with ≤ 60 DO exhibited significantly lower persistency and milk yield across all traits. These findings highlight the importance of integrating parity, calving timing, and DO management into strategic herd management practices. Optimizing these factors can substantially improve milk production, lactation performance, and overall farm efficiency, offering actionable insights for sustainable dairy farming. This study reinforces the need for evidence-based approaches to enhance productivity and support long-term dairy industry growth.