Automated devices used for the detection of estrus in
dairy cows function by continuously measuring some activity
parameters. Three such devices were tested (a PM
and two that recorded body activity). All three performed
well from the second postpartum ovulation or after day 50
postpartum. The poor performance at the first postpartum
ovulation was probably due to the weak expression of
estrus or due to silent ovulation, both of which are more
common at this stage in high-producing cows. This was not
a serious problem in our study because all the first ovulations
occurred before the recommended time for insemination
(from 50 days postpartum).