All data were statistically analyzed with SPSS (version
19.0, SPSS Inc., Munich, Germany). The effect of
sampling time on measured BHBA concentrations was
tested in a repeated-measures ANOVA repeating sampling
time. In a second approach, test characteristics of
a single BHBA measurement at a random time of the
day to diagnose SCK were determined using 2 different
cut-points (1.2 and 1.4 mmol/L) that are commonly
used to define SCK. The average daily BHBA concentration
calculated from the 8 measurements was used
as the gold standard to define a cow as healthy or as
having SCK. Cows were defined as healthy when the
average daily BHBA concentration was lower than the
respective cut-point (1.2 or 1.4 mmol/L) and as having
SCK when the cut-point was reached. Sensitivity
was calculated as the proportion of measurements that
correctly diagnosed a cow with SCK as having SCK (i.e., BHBA concentration measured at the particular
time of the day was equal to or above the cut-point
considered and the daily average BHBA concentration
was equal to or above the cut-point considered).