Associations between metabolic variables and hypocalcemia postcalving: Impact on metabolic diseases, milk production, and milk composition in dairy cows.

This research article reports an investigation of the associations among hypocalcemia types at calving, metabolic diseases, milk production, and milk composition in Holstein cows. A total of 100 Holstein-Friesian dairy cows (31 primiparous and 69 multiparous cows) from 4 farms were evaluated at multiple time points postpartum. The cows were categorized into 4 groups: normocalcemic (NC): primiparous: [Ca] >8.6 mg/dL at 1 and 2 DIM, multiparous: [Ca] >7.08 mg/dL at 1 DIM and >8.8 mg/dL at 4 DIM; transient subclinical hypocalcemia (tSCH): primiparous: [Ca] ≤8.6 mg/dL at 1 DIM and >8.6 mg/dL at 2 DIM, multiparous: [Ca] ≤7.08 mg/dL at 1 DIM and >8.8 mg/dL at 4 DIM; persistent subclinical hypocalcemia: primiparous: [Ca] ≤8.6 mg/dL at 1 and 2 DIM, multiparous: [Ca] ≤7.08 mg/dL at 1 DIM and ≤8.8 mg/dL at 4 DIM; and delayed subclinical hypocalcemia (dSCH): primiparous: [Ca] >8.6 mg/dL at 1 DIM and ≤8.6 mg/dL at 2 DIM, multiparous: [Ca] >7.08 mg/dL at 1 DIM and ≤8.8 mg/dL at 4 DIM. Serum Ca concentrations did not influence milk yield. However, significant differences were observed in serum malondialdehyde and total antioxidant capacity, as well as in milk SCS, between NC cows and other groups. At 1 DIM, cows with dSCH showed significantly elevated serum globulin, total protein, and albumin-to-globulin ratio, with lower albumin concentrations compared with NC cows. Cows in dSCH and tSCH also had a lower incidence of metritis and lower total cholesterol concentrations on d 1, 4, and 10 postpartum. Milk fat content at 100, 200, and 305 DIM differed significantly across different types of subclinical hypocalcemia compared with NC. Our results demonstrate that dairy cattle with dSCH have lower serum albumin and cholesterol concentrations, higher globulin concentration, and a disrupted albumin-to-globulin ratio. Changes in production indicators, such as reduced milk fat, increased SCS, and lower conception rate, indicate an active immune response and hidden inflammation. These findings confirm the dysregulation of the Calci-Inflammatory Axis in dSCH cases, highlighting the need to assess hypocalcemia as both a metabolic imbalance and a key indicator of immune and inflammatory health.