Evaluation of a Handheld Device for the Detection of ß-hydroxybutyrate Pre-calving in Dairy Cattle
Individual and herd ketone levels are commonly monitored in dairy cattle post-partum to identify individuals at-risk of metabolic disease and to identify potential improvements to management factors. The Precision Xtra® handheld meter has been validated for use in β-hydroxybutyrate (BHBA) measurements post-calving as a convenient cow-side test for ketonemia. Recent research has identified BHBA cut points pre-partum associated with increased risk of post-partum disease, but at much lower cut-offs than those indicating hyperketonia after calving: 0.6 to 0.8 mmol/L in comparison to 1.0 to 1.4 mmol/L. The objective of the current research is to validate the handheld device, Precision Xtra®, in the measurement of BHBA in whole blood against the gold standard method, laboratory evaluation of serum, to assess its diagnostic accuracy in detecting BHBA pre-calving in the range of 0.6 to 0.8 mmol/L.
As part of a larger study, 212 cows in 6 herds across southern Ontario were sampled between 3 and 9 days prior to the expected calving date. Blood was collected and tested on-site with the Precision Xtra® device. The serum portion of the sample was separated and sent to a laboratory for measurement of BHBA and non-esterified fatty acid (NEFA) concentrations. The results of the two BHBA measurement methods were compared and evaluated with concordance coefficients. The sensitivity and specificity of the Precision Xtra® were determined with Receiver Operator Characteristic curves at cut points of 0.6, 0.7 and 0.8 mmol/L. The two tests had a moderate concordance correlation of 0.77 ± 0.03 (CI95: 0.72 - 0.83) and the area under the curve for each cut point was high with values between 0.90 and 0.93. The Precision Xtra® had sensitivities of 85 to 93% and specificities of 76 to 87% depending on the cut point tested. The level of agreement between Precision Xtra® cut points and at-risk pre-calving NEFA concentrations of 0.4 and 0.5 mEq/L was calculated. The level of agreement between Precision Xtra® BHBA concentrations ≥ 0.8 mmol/L and NEFA concentrations ≥ 0.5 mEq/L was substantial, with a kappa of 0.64. Based on the moderate level of correlation and the good level of sensitivity and specificity, the Precision Xtra® is a valid tool in the detection of elevated BHBA pre-calving and may be helpful in identifying individuals at risk of metabolic disease.
Keywords: ketosis, beta-hydroxybutyrate, diagnostic test evaluation