Estrus signs in Holstein Friesian dairy cows and their reliability for ovulation detection in the context of visual estrus detection

The aim of the present study was to determine the frequency of estrus signs in housed dairy cows and to compare their reliability in relation to visual estrus detection, including all signs of estrus, which can be observed like cows' behavior (especially standing to be mounted) and physiological processes like the appearance of vaginal mucus. For the study, the estrous behavior of 139 cows was observed and reliability rates (RR) for each estrus sign were calculated. Visual estrus detection was performed three times daily for 30 minutes each and began at Day 21 postpartum and ended at Day 40 of gestation. Estrus signs were evaluated according to a three-point scoring system. Additionally, estrous cycle monitoring was carried out by transrectal ultrasonography and serum progesterone analyses. Ovulation was confirmed by the presence of a sonographically detected ovulation and a progesterone concentration of <= 1.0 ng / mL within 24 hours before or after ovulation, and served as strong indication for the results of the visual estrus detection (0v-estrus). It turned out that besides standing heat (standing-to-be-mounted by another cow for about three to seven seconds), the most reliable estrus signs were an increase in activity and participation in group activities of other cows in estrus (RR: 93.4 %), head resting in the back area of other cows for more than two seconds (RR: 86.7 %) and mounting of herd members (RR: 93.8 %). Though standing heat was the most reliable estrus sign (RR: 100.0 %), it was only observed in 22.3 % of all detected Ov-estrus events. By using these estrus signs for visual heat detection, a heat detection rate of 52.2 % was reached. In conclusion, since only half the estruses can be detected by visual estrus detection, it is essential to use especially the estrus signs with high RR in order to ensure sufficient estrus detection.