Production responses to various doses and ratios of estradiol benzoate and trenbolone acetate implants in steers and heifers.

At each of three locations, 400 steers and an equal number of heifers were randomized to 10 treatment groups. The purpose of the studies was to evaluate the response of feedlot steers and heifers to single implants containing a combination of estradiol benzoate (EB) and trenbolone acetate (TBA) at two different ratios each at three doses. The selected ratios corresponded to 1E2(estradiol-17 beta):5TBA and 1E2:10TBA. The two ratios were each tested at three different EB/TBA doses (1:5 at 20/70, 40/140, and 60 mg/210 mg, 1:10 and 14/100, 28/200, and 42 mg/300 mg). The test groups were compared to those given each of the compounds alone (60 mg of EB or 300 mg of TBA), as well as to groups reimplanted with Synovex S or Synovex H implants and untreated controls. Steers (P < .01) and heifers (P < .05) implanted with the 1:10 E2:TBA implants gained faster and had better feed conversion (FC) than their counterparts given 1:5 E2:TBA over the 140-d trial. The results indicated that both estradiol benzoate and trenbolone acetate contributed to the efficacy of the combination implant. Contour plots of ADG and FC indicate that increasing the amount of EB above approximately 36 and 37 mg does not significantly increase the response of steers. The results of these studies indicate that the 28 EB/200 TBA dose is close to optimal for growth promotion and feed conversion in both heifers and steers. In steers, carcass value was increased (P < .01) in all test groups except the group give TBA only. Despite a slight reduction in marbling score and percentage of Choice carcasses, carcasses of steers treated with either 28 mg of EB/200 mg of TBA or 42 mg of EB/300 mg of TBA were more valuable (P < .05) than carcasses from steers in any of the 1:10 ratio EB/TBA groups. Carcass values for groups reimplanted with Synovex S or Synovex H or implanted with EB alone were not significantly different from those for groups implanted with any dose of the 1:10 EB/TBA ratio.