Establishing biochemical thresholds for serum metabolites to predict single or multiple production diseases in crossbred transition dairy cows under tropical climatic conditions.

The current study aimed to establish biochemical threshold values for serum non-esterified fatty acids (NEFA), β-hydroxybutyric acid (BHBA), glucose, and calcium during prepartum period to predict the likelihood of postpartum production diseases (ketosis, milk fever, mastitis, and metritis) in Karan Fries (KF) cows under tropical climates of northern India. 31 KF cows were monitored from -6 weeks prepartum to +7 weeks postpartum, with blood sampling at -6, -3, -2, -1 weeks, on the day of calving, and +1, +2, +3, +5, +7 weeks. Based on postpartum production disease incidence, cows were classified as no production disease (NPD; n = 10), single production disease (SPD; n = 12), and multiple production diseases (MPD; n = 9). The MPD group exhibited significantly higher (P < 0.05) serum NEFA and BHBA levels from -3 and -1 weeks prepartum, respectively and lower (P < 0.05) glucose and calcium levels from -2 weeks and -1 week prepartum onward compared to SPD and NPD groups. Receiver Operating Characteristic (ROC) analysis identified NEFA ≥ 0.29 mmol/L (-1 week) as predictive of SPD, and ≥ 0.36 mmol/L (-1 week) as predictive of MPD. Similarly, BHBA ≥ 1.23 mmol/L (calving) indicated SPD and whereas > 1.40 mmol/L (-1 week) indicated MPD. Glucose ≤ 37.55 mg/dL at -2 and -1 weeks predicted SPD and MPD respectively, while calcium ≤ 6.60 mg/dL (calving) and ≤ 6.35 mg/dL (-1 week) were indicative of SPD and MPD. These evidence based thresholds provide reliable early biomarkers of postpartum production diseases, supporting routine biochemical monitoring and timely interventions to improve herd health and productivity under tropical dairy farming conditions.