PSVI-17 Effects of increasing doses of trenbolone acetate and estradiol on sera metabolites following implantation during the finishing phase in beef steers

Abstract

Abstract Continental × English crossbred beef steers (n = 240; allotment BW = 365 kg [SD 22.5]) were used in a randomized complete block design feedlot study designed to evaluate the effects that increasing doses of trenbolone acetate (TBA) and estradiol-17β (E2) have on sera urea-N (SUN) and sera insulin-like growth factor I (IGF-I). Steers were allotted to 30 pens (n = 8 steers/pen) at the Ruminant Nutrition Center (RNC) in Brookings, SD; and were then 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] administered 124 days before harvest. This study was part of a factorial experiment that included bedding application. No interactions were detected (P ≥ 0.26). Blood samples were collected and harvested as sera during the weighing process on d 1, 28, 56, and 84 prior to feeding from sentinel steers (n = 2 steers/pen) and pen served as the experimental unit. An implant × day interaction (P = 0.05) was noted for SUN. On d 28, NI cattle had the greater SUN (P = 0.05) compared to PL and CH was intermediate to NI and PL. No implant × day interaction (P = 0.52) was detected for sera IGF-I. However, sera IGF-I was increased (P = 0.01) 14.7% and 18.7% for CH and PL respectively compared to NI. Sera IGF-I also increased as days on feed increased (P = 0.01). Increasing doses of TBA and E2 resulted in increased anabolism as indicated by a reduction in SUN 28 d after implantation and increased sera IGF-I post-implantation.