Cows with BHBA concentrations
≥0.8 mmol/L at this time were enrolled in the trial
(n = 92). Subsequent BHBA measurements took place
every 3 h for a total of 8 measurements during 24 h.
The effect of sampling time on BHBA concentrations
was tested in a repeated-measures ANOVA repeating
sampling time. Sampling time did not affect BHBA
concentrations in continuously fed dairy cows. Defining
the average daily BHBA concentration calculated
from the 8 measurements as the gold standard, a single
measurement at a random time of the day to diagnose
subclinical ketosis had a sensitivity of 0.90 or 0.89 at the
2 BHBA cut-points (1.2 and 1.4 mmol/L).