217 Influence of daily temperature fluctuations on estrus activity determined by an electronic estrus detection system and conception to artificial insemination in cross-bred beef heifers

Abstract Behavioral estrus occurs in response to estradiol, and the intensity of activity registered in some electronic estrus monitoring systems is greater in dairy cows that conceive to artificial insemination compared to cows that do not conceive. Ambient temperature may influence estrus activity and follicular development. Therefore, we hypothesized that differences in temperature would associate with peak activity and conception to artificial insemination in cross-bred beef heifers. Heifers (n = 346) in south central Nebraska were observed twice daily for 21 d for behavioral estrus and artificially inseminated between June 4 and June 25, 2018. Onset of estrus and peak activity were extracted from the electronic system. Ambient temperature was merged with onset of estrus, and data were analyzed using the MIXED procedure of SAS with pregnancy status to artificial insemination as a class effect. There was no difference in peak activity between heifers that conceived to artificial insemination and heifers that did not conceive to artificial insemination (P = 0.45). The ambient temperature at onset of estrus was greater for heifers that did not conceive to artificial insemination than for heifers that conceived to artificial insemination (P < 0.05). Time of onset significantly influenced peak activity (P < 0.01), with the greatest peak activity occurring in the early morning hours and in the early evening hours. Daily temperatures increased until 1600 h and decreased thereafter (P < 0.01). Differences in peak activity do not associate with conception to artificial insemination in beef heifers as in dairy cows, but temperature at onset of estrus influenced conception to artificial insemination. Based on increased peak activity in the evening when temperatures were still greater than the early morning hours, the perceived trajectory of temperature may influence behavioral estrus more than the actual temperature. USDA is an equal opportunity provider and employer.