Evaluation of a portable ketometer for on-site monitoring of blood β-hydroxybutyrate concentrations in dairy sheep and goats

On-site measurement of blood β-hydroxybutyrate (BHB) concentration is a valuable tool to monitor the energy status in dairy ruminants. The aim of the study was to assess the agreement of a portable ketometer with standard laboratory method for on-site measurement of BHB in dairy sheep and goats. Three hundred and forty six animals from 12 farms were overall blood sampled: 237 dairy sheep (186 dry and 51 lactating) and 109 dairy goats (39 dry and 70 lactating). Agreement between the portable WellionVet BELUA device (WEL) and the laboratory method was evaluated for each group of animals with Bland-Altman plots and concordance correlation coefficients (CCC). Additionally sensitivity specificity and k-statistics for WEL at the BHB threshold of ≥0.8 mmol/L were calculated. BHB values with WEL were highly correlated to laboratory results. A systematic bias of ca. 0.2 mmol/L was observed in all groups of animals. With the addition of this bias as a correction factor, CCCs improved significantly (0.90-0.96 for sheep and 0.93-0.98 for goats). At the threshold of ≥0.8 mmol/L, sensitivity was 70.0%-94.1% for sheep and 87.5%-100.0% for goats, and specificity 94.1%-84.8% for sheep and 100.0% for goats. Moreover, dichotomized test agreement was moderate for dry sheep, substantial for all sheep and almost perfect for all other cases, when the correction factor was added. To conclude, WEL is a device with satisfactory agreement with laboratory values in small ruminants when a correction factor of 0.2 mmol/L is added on obtained BHB values.