Prevalence of subclinical hypocalcemia in dairy herds.

The prevalence of subclinical hypocalcemia in the transition cow is unknown. Cows with subclinical hypocalcemia have no clinical signs of hypocalcemia but may be more susceptible to other diseases. The objective of this study was to determine the prevalence of subclinical hypocalcemia in the US dairy herds. As a part of the United States Department of Agriculture's National Animal Health Monitoring System 2002 Dairy study, serum samples were collected from 1462 cows within 48 h of parturition. The samples were sorted by lactation number: 1st (n=454), 2nd (n=447), 3rd (n=291), 4th (n=166), 5th (n=72), and 6th (n=32). Subclinical hypocalcemia (<2.0 mM) increased with age and was present in 25%, 41%, 49%, 51%, 54%, and 42% of 1st-6th lactation cows, respectively. Cows with serum calcium concentrations >2.0 mM had significantly lower serum non-esterified fatty acids indicating better energy balance than those with subclinical hypocalcemia. Subclinical hypocalcemia may make cows more susceptible to secondary diseases but more research will be required to determine if this is true.