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.