Comparative Evaluation of Different Blood Collection Sites for the Assessment of Beta-Hydroxybutyric Acid Concentrations Using a Handheld Meter in Sheep.

Hyperketonaemia is a common problem in periparturient sheep. This study aimed to evaluate the performance of FreeStyle Optium Neo H (FS) for measuring blood β-hydroxybutyric acid (BHBA) concentrations in sheep. Whole-blood BHBA concentrations were measured using the FS from the jugular and ear veins of 175 clinically healthy, late-gestation (n = 56) and postparturient (n = 119) ewes. Jugular blood serum samples were also used for the reference sampling site. Blood BHBA concentrations measured with the FS from the jugular and ear veins showed a high positive correlation with the serum concentrations measured using the reference method (r = 0.84, r = 0.81, respectively). According to the Bland-Altman plot and limits of agreement, when compared to the reference method, FS recorded lower BHBA concentrations of 0.03 and 0.04 mmol/L from the jugular and ear veins, respectively. Passing-Bablok regression analysis revealed an intercept of -0.125 (95% CI: -0.148 to -0.078) and a slope of 1.250 (95% CI: 1.111-1.304) for the jugular vein and an intercept of -0.005 (95% CI: -0.089 to -0.018) and a slope of 1.000 (95% CI: 0.909-1.111) for the ear vein. The receiver operating characteristics (ROC) analysis determined that the optimal thresholds of the FS for the jugular and ear veins were, respectively, ≥0.8 mmol/L (sensitivity, 87.5%; specificity, 97.6%, AUC, 0.896) and ≥0.6 mmol/L (sensitivity, 87.5%; specificity, 91.0%, AUC, 0.887) for the identification of sheep with pregnancy toxaemia (PT). In conclusion, although there was constant and proportional errors indicating non-agreement with the reference method in the Passing-Bablok regression equation, FS's diagnostic performance was good enough to identify ewes with PT or hyperketonaemia.