Reliability of estrous detection in Holstein heifers using a radiotelemetric pedometer located on the neck or legs under different rearing conditions.

To evaluate the efficiency and accuracy of estrous detection using a new pedometry system that can measure the hourly activity of cattle, pedometers were attached to the neck and the hind legs of 15 Holstein heifers. Heifers were reared in pasture for grazing, an open paddock, or in a tie-stall barn (an additional pedometer was attached to a front leg of each of these heifers). The most recent 24 h-total number of steps was compared for each 1 h-interval with the mean value of the preceding days during the reference period (RP). The neck pedometer detected all 10 instances of estrous activity (100%) for the grazing heifers at 1.3 times the thresholds value for a 5-day RP but with only 32% accuracy. The hind leg pedometer, however, obtained 100% efficiency and 83% accuracy at 1.4 times the threshold value for a 7-day RP. The efficiencies and accuracies in detecting 12 instances of estrous activity under the paddock condition were 92 and 65% (neck, 1.3-fold, 7-day RP) and 92 and 100% (hind leg, 1.6- or 1.7-fold, 7-day RP), respectively. Under the tie stall condition, the neck pedometers detected 92% of 23 instances of estrous activity with 34% accuracy (1.2-fold, 3-day RP), and the efficiencies and accuracies of the leg pedometers were 78 and 78% (hind leg, 1.4-fold, 4- or 6-day RP) and 87 and 83% (front leg, 1.4-fold, 7-day RP), respectively. Prediction of ovulation time was more precisely with the leg pedometers than with those under the tie stall conditions. Our preliminary results indicate that this new pedometer system has practical value for estrous detection in heifers under different rearing conditions, which affect the criteria required for detection. Furthermore, they also indicate that a leg pedometer can reliably detect estrus and that a neck pedometer may only be capable of detecting estrus under paddock rearing conditions.