Critical thresholds of Ion Concentration in Plasma for Hypocalcemia prediction in dairy cows using receiver operating characteristic (ROC) analysis

Postpartum hypocalcemia is an important nutrient metabolic disease which occurs frequently in dairy cows. Parameters for early risk prediction of hypocalcemia have not been investigated previously in dairy cows on farms in China. To predict the occurrence of hypocalcemia and obtain the critical thresholds of various parameters related to the prevalence and risk of hypocalcemia in dairy cows. 61 Holstein Friesian cows from one farm were randomly selected and monitored using a plasma calcium (Ca)concentration of 2.0 mmol/L as the cutoff point of hypocalcemia. The risk prediction thresholdsfor hypocalcemia were determined by receiver operating characteristic (ROC) analysis using prenatal plasma Ca concentration and other electrolyte concentrations. The results showed that the plasma thresholds were more than 2.12 mmol/L for Ca before calving, with 98.7% sensitivityand 88.5% specificity, and more than 1.90 mmol/L for phosphorus (P), with 98.7% sensitivity and 65.4% specificity, respectively. Furthermore, there was a prominent positive correlation between the plasma concentration of Ca and that of P or magnesium (Mg) before calving in dairy cows. Levels of Ca and P in the plasma of dairy cows before calving are useful parameters for risk prediction of postpartum hypocalcemia incidents in dairy cows.