Comparison of three estrus detection systems during summer in a large commercial dairy herd

The objective of the study was to compare three systems for estrus detection and combinations of these systems on a large commercial dairy (1075 lactating cows) during stress of summer heat. At 37-45 days in milk (DIM), 255 cows were fitted with a HeatWatch® device (HW; DDx Inc., Denver, CO), an activity sensor ALPRO® (ALPRO; DeLaval Inc., Kansas City, MO), and visually observed (VO) three times daily. Pregnancy status was determined by uterine palpation per rectum 35-49 days following artificial insemination (AI). Effects of DIM, parity, standing events, inseminator, and interval between onset of estrus and AI on conception rates were determined using logistic regression. Efficiencies for detection of estrus, determined by comparing detected periods of estrus with a theoretical total of 570 periods, were 49.3% (VO), 37.2% (ALPRO), 48.0% (HW), and 80.2% for all three systems simultaneously. Conception rates (LSM ± S.E.) for cows detected by one or more of the three systems were 6.2 ± 3.9 for VO, 19.8 ± 5.6 for ALPRO, 17.3 ± 5.0 for HW, 22.8 ± 7.0 for VO + ALPRO, 26.9 ± 4.6 for VO + HW, 23.2 ± 5.2 for ALPRO + HW, and 18.4 ± 4.7 for VO + ALPRO + HW. Inseminations performed during no and mild heat stress (temperature-humidity index; THI ≤ 76) had greater conception rate (P < 0.05; 38.8%) compared to AI performed during moderated heat stress conditions (THI > 76; 17.6%). Number of mounts were higher for primiparous versus multiparous cows (P < 0.05). Cows over 80 DIM during estrus exhibited fewer (P < 0.05) standing events. The highest conception rate occurred with the combination of VO + HW, which confirms the premise that combination of multiple systems enhances both the efficiency and accuracy of estrus detection.