The present results were obtained from observations on
one herd, so extrapolations need to be considered with
caution. The cows were fed in individual, raised troughs;
so repeated, wide head movements would have been
possible, reducing the accuracy of devices attached to neck
collars. Moreover, our validation of the estrus alerts was
based on ovulations identified using only data from P4 assays
in milk and not from video records that allow quantification
of estrus expression (duration and intensity). We
are cautious about interpretation because FP alerts can be
caused by overactivity in the cows induced by their environment
and because FN alerts could be caused by silent
ovulation. Between 9% and 16% of dairy cows have at least
one ovulation of ranks 2 to 4 that are not accompanied by
estrus [30], so some FN alerts are almost certainly due to
these silent ovulations and the performance of the devices
could be underestimated in our study. Finally, we did not
study the conception rates and the timing for insemination
because of the experimental design (each cow fitted with
the three devices), and these aspects should be further
investigated [31,32].
The detection of estrus was influenced mainly by
ovulation rank. Sensitivity for the first postpartum ovulation
varied from 23% to 40% (depending on the device)
compared with 78% to 86% for subsequent ovulations.
These observations are consistent with those from previous
studies [8,16]. It is known that 50% to 80% of first ovulations
postpartum are silent [30,33]. We did not have continuous
video recording in the study to check which first postpartum
ovulations were accompanied by estrus, but it is
very likely that the poor performance of all three devices
at the first postpartum ovulation was related to low