Impacts of Estrus Expression and Intensity during a Fixed-Time AI Protocol on Parameters Associated with Fertility and Pregnancy Success in Beef Cows

In this experiment (d 0 to 41), 290 lactating, primiparous and multiparous non-pregnant Brangus cows received a 2 mg injection of estradiol benzoate and an intravaginal progesterone (P4) releasing device (CIDR) on d 0, a 12.5 mg injection of PGF_2α on d 7, CIDR removal in addition to 0.6 mg injection of estradiol cypionate and 300 IU injection of eCG on d 9, and fixed-time AI on d 11. All cows were inseminated by the same technician with semen from a single bull. On d 7, cows were fitted with a pedometer behind their left shoulder. On d 9, an estrus detection patch was attached to the tailhed of each cow. On d 11, estrus was defined as removal of >50% of the rub-off coating from the patch. Cow activity (total steps) was calculated by subtracting d 7 to 9 results (basal activity) from d 9 to 11 results (expected estrus period). Cows were classified by estrus intensity according to physical activity as: NOESTRUS = cows that did not express estrus; or cows that expressed estrus with physical activity below (LOWESTRUS) or above (HIESTRUS) the population median. Ovarian transrectal ultrasonography was performed on d 11 and 18. Blood was collected concurrently with ultrasonography exams for plasma P4 analysis. Pregnancy status was verified by transrectal ultrasonography on d 41. Only data from cows that ovulated to the synchronization protocol and that were successfully classified according to estrus characteristics were utilized (NOESTRUS, n = 57; LOWESTRUS, n = 87; HIESTRUS, n = 90). Diameter of dominant follicle on d 11, CL volume on d 18, and plasma P4 concentrations on d 18 were greater (P ≤ 0.05) in HIESTRUS vs. LOWESTRUS and NOESTRUS, and also greater (P ≤ 0.05) for LOWESTRUS vs. NOESTRUS (14.1, 13.4, and 12.5 mm, SEM = 0.3; 5.5, 4.9, and 3.6 cm³, SEM = 0.5; and 4.7, 4.0, and 3.0 ng/mL; SEM = 0.2). Plasma P4 on d 11 were greater (P < 0.01) in NOESTRUS vs. HIESTRUS and LOWESTRUS, and similar (P = 0.36) between HIESTRUS and LOWESTRUS (0.47, 0.30, and 0.25 ng/mL; SEM = 0.07). Pregnancy rates were less (P ≤ 0.04) in NOESTRUS vs. HIESTRUS and LOWESTRUS, and similar (P = 0.38) between HIESTRUS and LOWESTRUS (42.0, 67.3 and 60.5, SEM = 7.1). Hence, estrus expression and intensity, estimated by physical activity after CIDR removal, impacted fertility parameters and pregnancy success in Brangus cows.