LAUSR

Two hundred and forty Continental x English beef steers (BW = 805 lbs [SD 49.6]) were used to evaluate increasing doses of trenbolone acetate (TBA) and estradiol-17β (E2) in terminal implant during the finishing phase. Steers were assigned to 1 of 3 treatments: no implant (NI), Synovex Choice (100 mg TBA + ~10 mg E2; CH), or Synovex Plus (200 mg TBA + ~20 mg E2; PL). This experiment was part of a factorial experiment that included bedding application. No interactions between implant and bedding were detected (P ≥ 0.09). The basal diet consisted of dry-rolled corn, dried distillers grains plus solubles, oatlage, and a liquid supplement that provided 30 g/ton of monensin sodium. The diet delivered 14.2% crude protein, 95.1 Mcal/cwt of NEm, and 63.7 Mcal/cwt of NEg. Combination TBA + E2 implants increased (P ≤ 0.02) final BW, ADG, DMI, and decreased F:G, and increased HCW, and REA at equal BF accumulation without detriment to marbling score. Introduction There is currently no other technology available to cattle producers that can match the performance improvements following steroidal implant administration in finishing steers. Steroidal implants have been used in U.S. commercial beef production for over 60 y and have been shown to increase ADG and decrease F:G in feedlot cattle compared to non-implanted cattle (Reinhardt, 2007). In 2013, APHIS reported that more than 90% of cattle entering the feedlot are given at least one implant. In some situations, use of two sequential implants is preferred. This depends primarily on type of implant and implant window, typically a terminal implant window is considered to last for approximately 60 to 120 days. The objective was to evaluate the effects of increasing doses of TBA and E2 on finishing phase growth performance and carcass trait responses. Experimental Procedures Steers were housed at the Ruminant Nutrition Center in Brookings, SD in 25 ft x 25 ft concrete surface pens with 37.2 in of bunk space/hd. Continental x English steers (n = 240, BW = 805 lbs [SD 49.6]) were allotted to 30 pens 36 d prior to being implanted. Initial processing included weighing, ear tagging, and rectal temperature measurement along with vaccination for bovine respiratory syncytial virus (BRSV), bovine rhinotracheitis (IBR), bovine viral diarrhea (BVD) Types 1 and 2, parainfluenza 3 (PI3), Mannheimia haemolytica (pasteurella), and clostridium perfringens type A. Cattle were re-vaccinated 36 days after initial processing for clostridium perfringens type A and were poured with a paraciticide. Pens were assigned to 1 of 3 treatments: 1) No implant (NI), 2) Synovex Choice (100 mg TBA + ~10 mg E2; CH), or 3) Synovex Plus (200 mg TBA + ~20 mg E2; PL) on d 1. The first 6 pen replicates began on test 14 d prior to the last 4 pen replicates due to weather challenges at the time of cattle acquisition. A common diet consisting of dry-rolled corn, dried distillers grains, and oatlage or grass hay was fed that contained 14.2% crude protein, 95.1 Mcal/cwt of NEm, and 63.7 Mcal/cwt of NEg. A