Automated activity monitoring and visual observation of estrus in a herd of loose housed Hereford cattle: Diagnostic accuracy and time to ovulation.

A prospective cohort study was performed in the purebred Hereford herd at Götala Beef and Lamb Research Centre, Sweden. The study's first objective was to assess the ability of an automatic activity monitoring system (AAMS) to detect estrus in beef suckler cows, and its second objective was to estimate the time from estrus to ovulation. The study sample (n = 38) consisted of 14 Hereford heifers and 24 Hereford cows. Standardized visual observation of estrus was performed for 20 minutes thrice daily, and animal activity was recorded with an AAMS system, Heatime (SCR Engineers Ltd., Israel). Cows in estrus underwent transrectal ultrasonography every 8 hours, to estimate the time of ovulation. Blood samples for progesterone analysis were collected thrice weekly throughout the study period. A cutoff value of 1-ng progesterone/mL of serum was used to define luteal activity. The AAMS had a 90% (95% confidence interval [CI] 77%-97%) sensitivity and 100% specificity (95% CI 94%-100%), and visual detection of estrus had a 77% sensitivity (95% CI 62%-88%) and a 89% specificity (95% CI 79%-95%) for identifying estrus when compared to the gold standard defined by temporal pattern of serum progesterone concentration. When both methods were used in parallel, the sensitivity increased to 96% (95% CI 86%-99%), and the specificity increased to 90% (95% CI 80%-96%). The time of ovulation after estrus was determined on 50 occasions. The median estrus (AAMS detected) to ovulation interval was 25 hours for heifers and 23 hours for cows (interquartile range 11-29 hours and 19-25 hours, respectively). The median estrus (visually detected) to ovulation interval was 28 hours for heifers and 21 hours for cows (interquartile range 13-29 hours for both categories). In conclusion, the AAMS had both a higher sensitivity and specificity for estrus detection than thrice-daily visual observation. The time from detection of estrus to ovulation observed in this study indicates that reproductive performance might be improved if Hereford cattle are inseminated sooner after detection of estrus than is currently recommended.