Associations of β-hydroxybutyrate, cholesterol, triglycerides and high-density lipoproteins to non-esterified fatty acids pre- and postpartum.

While laboratory tests for measuring the concentration of NEFA in serum are well established, a point of care test to determine NEFA on farm is not available. Several hand-held measuring devices, however, have been validated for measuring β-hydroxybutyrate (BHBA) in cattle or cholesterol, triglycerides (TAG), and high-density lipoproteins (HDL) in human medicine, respectively. The objective of this study was to evaluate the association between NEFA and different parameters related to lipid metabolism. Specifically, we set out to determine if it is feasible to predict the concentration of NEFA by means of surrogate measures. The concentration of BHBA was determined by a hand-held device evaluated for use in cows, whereas the concentrations of the other parameters were determined by laboratory analysis because hand-held devices for cholesterol, TAG and HDL are only evaluated for human medicine so far. A total of 254 cows were included in the trial. One blood sample was taken from each cow between d 10 and d 1 prepartum. Second and third samples were collected on d 2 and d 10 postpartum, respectively. The coefficients of correlation between parameters were calculated and a receiver-operator characteristic curve analysis has been used. The prediction of NEFA concentrations using only one of the parameters was insufficient. However, a NEFA concentration ≥0·5 mEq/l could be predicted with a high sensitivity (i.e. Se = 0·88) and specificity (i.e. Sp = 0·93) from d 3 to d 1 prepartum and a NEFA concentration ≥0·7 mEq/l could be reliably predicted on d 2 postpartum (i.e. AUC = 0·89, Se = 0·89, Sp = 0·76) when using a combination of BHBA, cholesterol and TAG as surrogates. Overall, our results suggest that a combination of different parameters of lipid metabolism could be used as surrogates for NEFA.