Body condition score at calving, subclinical ketosis, postpartum body condition score losses, diseases, and fertility in Holstein cows: modelling confounding associations.

This study examined the association between energy metabolism-related variables and conception rate at first service (CRFS) in Holstein cows. It focused on identifying confounding relationships among key factors. Data came from a large dairy farm in Coahuila, Mexico. The dataset included 1056 lactations recorded in 2024. Of these, 419 were primiparous and 637 were multiparous cows. Only cows that completed a synchronization protocol and received timed artificial insemination (TAI) were included. A logistic regression model was used to predict CRFS. In the model, body condition score (BCS) at calving and postpartum diseases were not significant when subclinical ketosis (SCK) and BCS loss were included. This suggested confounding effects. Key associations were found: Cows with BCS ≥ 3.75 at calving were 5.55 times more likely to lose ≥ 0.75 BCS units by first breeding than cows with BCS ≤ 3.5. Cows with BCS ≤ 3.5 at calving were 0.45 times as likely to develop SCK compared to cows with BCS ≥ 3.75. Cows with postpartum diseases were 4.42 times more likely to develop SCK than healthy cows. Multicollinearity was observed between postpartum diseases and SCK and between BCS at calving and postpartum BCS loss. The best-fitting model for CRFS included: breeding season, milk yield at week 8 postpartum, parity, SCK, and postpartum BCS loss. SCK and BCS losses, as well as postpartum diseases, were key factors associated with CRFS and were also confounded by BCS at calving.