Characteristics and prediction of subclinical hypocalcemia in dairy cows during the transition period using blood analytes

This study aimed to present the characteristics of and to predict subclinical hypocalcemia in dairy cows during the transition period using blood analytes. We examined fluctuations in plasma calcium (Ca), phosphorus (P), bone metabolic markers carboxy-terminal telopeptide of type I collagen (CTX), fibroblast growth factor (FGF23), 1,25(OH)2D3, parathyroid hormone, and other blood biochemical analytes from prepartum week 2 to postpartum day 14 in 116 multiparous high-producing Holstein cows from a free-stall barn dairy farm. With a plasma concentration of Ca <2.0 mmol/L as a criterion for the diagnosis of subclinical hypocalcemia, 64 cows were classified as normocalcemic, and 52 cows as subclinically hypocalcemic. Among the 52 hypocalcemic cows, 50 were detected on postpartum days 1 or 3, and 2 on postpartum day. The subclinically hypocalcemic cows were in a state of low bone turnover in the prepartum period, with low plasma concentrations of Ca and CTX. The subclinically hypocalcemic cows showed signs of a P regulation disorder in the prepartum period. This was marked by high plasma concentrations of P and low concentrations of 1,25(OH)2D3 and FGF23, which is also considered to be the cause of the low bone turnover. The results of a multiple logistic regression model showed that prepartum plasma concentrations of FGF23, CTX, and Ca were ideal predictors of postpartum subclinical hypocalcemia in dairy cows, using the model equation 38.8-0.052*FGF23-0.492*CTX-10.645*Ca, with a score of > 0 considered as an indication of increased risk of subclinical hypocalcemia after calving. The scoring rule had an accuracy of 79.3%, sensitivity of 76.9%, and specificity of 81.3%. The plasma concentrations of FGF23, CTX, and Ca were ideal predictors of postpartum subclinical hypocalcemia in dairy cows.