Estrus and Luteal Activity of Postpartum Beef Cows After Treatment with Estradiol

Multiparous Hereford × Angus postpartum cows were used to determine the effects of treatment with estradiol cypionate (ECP) on estrus and luteal activity (LA) of thin (<5 BCS) cows at 25 or 50 d after calving, and moderate (≥5 BCS) cows at 25 d after calving. Ovaries were examined by ultrasonography at treatment, and plasma progesterone concentrations were used to verify the absence of corpora lutea. Treatment of cows with ECP at 25 d after calving increased (P < 0.01) the incidence of estrus within 4 d after treatment in moderate (55 vs. 11%) and thin (50 vs. 0%) cows compared with control cows. Treatment of thin cows with ECP at 50 d after calving increased (P < 0.01) estrus within 4 d (50 vs. 0%). Treatment with ECP did not influence LA (progesterone >1 ng/mL for 1 d) within 10 d after treatment (P = 0.52). Days to normal LA were greater (P = 0.02) for thin and moderate cows treated with ECP at 25 d after calving (74 ± 5 d) compared with control cows (61 ± 5 d), and ECP treatment tended to increase (P = 0.07) days to LA for thin cows treated at 50 d after calving. Although ECP induced estrus in beef cows during the first 50 d after calving, normal luteal function was not initiated.