Association between subclinical ketosis, body condition score, and pregnancy at first artificial insemination in Holstein cows calving at different seasons.

The objective was to test the association of BCS at calving and incidence of subclinical ketosis (SCK) with pregnancy at first insemination (PAI1) in Holstein cows calving in different seasons, housed in a large dairy in Mexico. This retrospective observational study used data from 1,904 Holstein cows calving from October 2022 to October 2023 in a commercial dairy in Torreon, Coahuila, Mexico. Cows housed in a dry-lot system were tested for SCK at 5 ± 2 DIM using a hand-held device (FreeStyle Optium Neo, Abbott). Test results were considered positive when blood BHB >1.2 mmol/L. Cows were submitted to AI1 at 77 ± 2 DIM, following a double OvSynch protocol. Cows were scored for body condition at calving (BCS_C; n = 1,820) and at first AI (BCS_AI; n = 614). Subsequently, BCS_C and BCS_AI were categorized into 3 categories (low [<3.25]; medium [3.25–3.75]; and high [>3.75]), and cows were grouped in primiparous and multiparous. Data were examined using ANOVA and logistic regression. Multivariable models considered calving season, BCS_C, BCS_AI, the occurrence of retained fetal membranes and metritis, and milk yield at wk 4 and 8 as covariables. Mean ± SE BHB was 0.86 ± 0.01 mmol/L, and no differences were identified by the BCS_C category. The BHB concentrations were lower in cows calving in winter (0.83 ± 0.02 mmol/L; P = 0.02) and fall (0.86 ± 0.02 mmol/L; P = 0.04) than in cows calving in spring (0.94 ± 0.03 mmol/L). The adjusted odds (95% CI) of SCK in spring calvings were 2.05 (1.12–3.76) times the odds of SCK in winter calvings. No association between BCS_C or BCS_AI and PAI1 was identified. However, PAI1 was 32.4% versus 51.7% in cows with SCK versus nonaffected cows (P = 0.02). It is concluded that the incidence of SCK was associated with calving season, but there was no association between BCS at calving and SCK. Body condition at calving and BCS at first AI were not associated with PAI1, but a greater incidence of SCK resulted in lower fertility at first artificial insemination.