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Subclinical ketosis (SCK), an important disease in lactating dairy cows, is defined as the presence of elevated concentrations of circulating ketone bodies without the development of clinical signs. Therefore, diagnostic methods are limited to the detection of the concentrations of ketone bodies in different body fluids. The objective of this study was to evaluate a recently developed electronic hand- held meter (NovaVet) for the determination of β-hydroxybutyric acid (BHB) in the blood of dairy cows.
A total of 155 lactating dairy cows were included in the trial. Blood samples were taken from each cow and analyzed using the BHB meter. The obtained concentrations were compared to the results determined by a commercial laboratory. The Spearman's rank correlation coefficient was determined between the two methods. A Wilcoxon test was performed and a Bland-Altman plot was generated. Test characteristics (sensitivity, specificity, positive and negative predictive value) for established BHB cut points for the diagnosis of SCK were calculated using receiver operating characteristic (ROC) analysis.
The two methods were highly correlated (rs = 0.87; p < 0.05). A difference (median 0.0 mmol/l; interquartile range [IQR] -0.1 to 0.2 mmol/l; p < 0.05) was found between BHB concentrations determined using the BHB meter (median 1.0 mmol/l; IQR 0.7-1.3 mmol/l) and by the laboratory (median 0.9 mmol/l; IQR 0.7-1.1 mmol/l). Using a cut point of 1.2 mmol/l, sensitivity and specificity of the BHB meter were 97% and 82%, respectively.
There was a good agreement between BHB concentrations determined using the BHB meter and the laboratory. Furthermore, the BHB meter displayed good test characteristics. The specificity of 82% results in a number of false-positive results. However, this new device can be recommended for the detection of SCK in cows under practical conditions.