Impact of Summer Calving on Milk Production, Reproduction, and Culling Risk in Organic Dairy Cattle

The objective of this study was to evaluate the impact of summer calving on reproductive performance, milk yield, and culling risk in U.S. organic dairy herds. Data were obtained from Dairy Herd Improvement records of 483 organic dairy herds across 31 states, com-prising 323,304 calving records from 2018 to 2022. Calving months were categorized as winter, spring, summer, or fall. Mixed models were used to analyze 305-d milk yield, 305-d energy corrected milk yield, peak milk DIM, peak test day milk yield and logistic re-gression and survival analyses were applied to analyze calving difficulty, abortion, preg-nancy diagnosis, and culling outcomes. Cows calving during summer had fewer days to first service and fewer days open compared with cows calving in other seasons; however, their odds of being diagnosed pregnant were significantly lower. Summer-calving cows produced lower 305-d milk and energy-corrected milk yields, reached peak milk produc-tion later, and had lower peak test-day milk yield. Calving during summer was also asso-ciated with increased odds of calving difficulty and a higher risk of culling. These findings indicate that summer calving poses distinct challenges for organic dairy cows, with cu-mulative effects on fertility, milk production, and survivability, underscoring the need for season-specific management strategies in organic dairy systems.