TRENBOLONE ACETATE ESTRADIOL COMBINATIONS IN FEEDLOT STEERS - DOSE-RESPONSE AND IMPLANT CARRIER EFFECTS

Two experiments were conducted at three locations to determine the correct dosage and carrier for trenbolone acetate (TBA) and estradiol (E2) implants in feedlot steers. In the dose-response experiment, 1,296 steers were allotted to six implant treatments (48 pens per location): control, 140 mg of TBA (1 40/0), 30 mg of E2 (0/30), 20 mg of TBA + 4 mg of E2(20/4), 80 mg of TBA + 16 mg of E2(80/16), and 140 mg of TBA + 28 mg of E2 (140/28). In the carrier experiment, 575 steers were allotted to five implant treatments (25 pens per location): control, 140 mg of TBA + 28 mg of E2 in lactose (140/28-LA), 140 mg of TBA + 28 mg of E2 in cholesterol (140/28-CH), 140 mg of TBA + 20 mg of E2 in LA (140/20-LA), and 200 mg of progesterone + 20 mg of E2 benzoate (SS, reimplanted). In both experiments steers were fed a finishing diet for 140 to 168 d. In the dose-response experiment, response to TBA alone (140/0) did not differ from control (P > .2). Estradiol alone (0/30) improved ADG by 7% (P < .01) and tended to improve feed efficiency over control (3%, P = .17). The highest dosage (140/28) improved ADG by 18% (P < .001) and feed efficiency by 10% (P < .001) over control and 10% (P < .001) and 7% (P < . 01) over E2 alone, respectively. In the carrier experiment, all implant treatments increased steer performance over control (P < .01); no differences in response were observed (P > .2) between LA and CH carriers or between 28 and 20 mg of E2 in combination with 140 mg of TBA. Implant treatments, in general, decreased (P < .05) carcass fatness and quality grade; little difference was noted in carcass characteristics between E2 alone and treatments containing TBA. Combinations of TBA/E2 were more effective enhancers of steer performance under U.S. conditions than was either E2 or TBA alone (Exp. 1), and combinations were similar to SS-reimplanted (Exp. 2).