Impacts of estrus expression and intensity during estrus synchronization + artificial insemination protocol on parameters associated with fertility and pregnancy establishment in beef females

Abstract

In beef females, estrus expression during the synchronization + artificial insemination (AI) protocol has positive impacts on conception rates by modulating ovarian function, embryo development, as well as maternal pregnancy recognition. Recent research also demonstrated that estrus intensity, assessed via activation level of estrus detection Estrotect patches, was positively associated with circulating concentrations of pregnancy-associated glycoproteins (PAGs) e consequently with embryo viability in beef cows. However, additional research is required to further understand fertility and pregnancy establishment parameters associated with estrus expression, as well as better characterize estrus intensity in beef females. One alternative for the latter subject is the use of pedometers during the estrus synchronization protocol to estimate cow physical activity, which is a directly associated with estrus intensity. Therefore, the objective of the experiment proposed herein is to evaluate the impacts of estrus expression and intensity on parameters associated with fertility and pregnancy establishment in beef cows, Four hundred multiparous, lactating Nelore cows, averaging 70 to 90 days post-partum, will be assigned to an estrus synchronization + AI protocol: day -11) 2 mg of estradiol benzoate and intravaginal device containing 1.9 g of progesterone; day -4) 12,5 mg of prostaglandin F2±; day -2) intravaginal device removal + 0,6 mg of estradiol cypionate + 300 UI of eCG; and day 0) fixed-time AI. All cows will be inseminated by the same technician, with semen from a single bull and batch. On day -4, 1 pedometer will be attached on top of the right shoulder of each cow, placed inside a polyester bag. On day -2, cow physical activity (steps per day) will be assessed and considered basal activity, whereas estrus detection Estrotect patches will be attached to tail base of each cow. On day 0, estrus detection patches and pedometers will be evaluated. Cows will be classified as estrus expression or not according to activation of the estrus detection patch. In addition, within cows that expressed estrus, cows will be classified as low intensity estrus (50% of population with less physical activity) or high-intensity estrus (50% of population with greater physical activity). Ovarian ultrasonography will be performed at the time of AI (day 0) and 7 days post-AI (day 7) to determine ovulation and synchronization rates, as well as follicular diameters (day 0) and corpus luteum volume (day 7). Blood will be collected concurrently with ovarian ultrasonography exams and analyzed for plasma estradiol (day 0) and progesterone (days 0 and 7) concentrations. On day 20 post-AI, blood will be collected in RNA-specific tubes and subsequently analyzed for mRNA expression of interferon-stimulated genes. On day 30 post-AI, blood will be collected for the analysis of plasma concentrations of PAGs, and pregnancy diagnosis will be performed via ultrasonography. Final pregnancy rates will be determined according to calving rate. The resultant information will help elucidating why estrus expression and intensity enhance reproductive efficiency of beef cows, including maternal and pregnancy parameters. These results will directly contribute to strategies that enhance reproductive efficiency in beef females assigned to estrus synchronization + AI protocols. (AU)