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 impl ants containing a combination of estradiol benzoate (EB) and trenbolon e acetate (TEA) at two different ratios each at three doses. The selec ted ratios corresponded to 1E(2)(estradiol-17 beta):5TBA and 1E(2): 10 TBA. 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 at 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 TEA), as well as to groups r eimplanted with Synovex S(R) or Synovex H(R) implants and untreated co ntrols. Steers (P <.01) and heifers (P <.05) implanted with the 1:10 E (2):TBA implants gained faster and had better feed conversion (FC) tha n their counterparts given 1:5 E(2):TBA over the 140-d trial. The resu lts indicated that both estradiol benzoate and trenbolone acetate cont ributed to the efficacy of the combination implant. Contour plots of A DG and FC indicate that increasing the amount of EB above approximatel y 36 or 37 mg does not significantly increase the response of steers. The results of these studies indicate that the 28 EB/200 TEA dose is c lose to optimal for growth promotion and feed conversion in both heife rs and steers. In steers, carcass value was increased (P <.01) in all test groups except the group given TEA only. Despite a slight reductio n in marbling score and percentage of Choice carcasses, carcasses of s teers treated with either 28 mg of EB/200 mg of TEA or 42 mg of EB/300 mg of TEA were more valuable (P <.05) than carcasses from steers in a ny of the 1:10 ratio EB/TBA groups. Carcass values for groups reimplan ted with Synovex S or Synovex H or implanted with EB alone were not si gnificantly different from those for groups implanted with any dose of the 1:10 EB/TBA ratio.