ASAS/ADSA Production, Management, and Environment: Waste Management for Beef and Swine; Reproductive Practices and Measures 1036 Decreasing nitrogen losses from open-dirt feedlot pens by manipulation of organic matter excretion

Two trials were conducted to quantify effects of estradiol benzoate (EB) administration on fertility after removal of a controlled internal drug release (CIDR) r insert. Lactating, primiand multiparous Brangus females were administered a CIDR (1.38g Progesterone) for 7 or 8 d with prostaglandin F2α (25 mg, im) administered upon removal of the CIDR (control group). Females allotted to the treatment group were administered estradiol benzoate (EB, 1 mg,im) at 24 h post-CIDR removal. Females were observed twice daily for signs of estrus behavior for 5 d after CIDR removal. In Trial 1, females were inseminated 12 h postonset of estrus. The synchrony rate (SR; 93.9%) in EB treated (n = 82) females was higher (P < 0.01) than the SR (80.0%) in the control group (n = 230). First service conception rate (FSCR) was not affected (P > 0.1) by EB treatment (50.6 and 46.4% for treatment and control groups, respectively). However, females in the treatment group had a higher (P = 0.08) first service pregnancy rate (FSPR) than females in the control group (47.6 vs. 36.7%, respectively). In Trial 2, recipient cows received a single embryo 6.5 to 7.5 d post-onset of estrus. SR was higher (P < 0.01) in EB treated (n = 886) females compared to control (n = 457) females (93.0 and 73.5%, respectively). FSCR did not differ (P > 0.1) between control and treatment groups (54.4 and 55.7%, respectively). FSPR was higher (P < 0.01) in EB females (46.1%) compared to females in the control group (38.1%). In conclusion, the addition of an injection of 1 mg EB administered 24 h after a conventional CIDR synchronization treatment regimen increased both SR and FSPR following either AI or ET, in Brangus females.