USE OF GENETICALLY IDENTICAL (CLONE) STEERS TO DETERMINE THE EFFECTS OF ESTROGENIC AND ANDROGENIC IMPLANTS ON BEEF QUALITY AND PALATABILITY CHARACTERISTICS

Six sets of four genetically identical Brangus steers (n = 24; mean weight = 413 kg, SD = 19.8) were used to study the effects of estradiol and trenbolone acetate on beef quality and palatability characteristics. Steers in each clone set were randomly assigned to the following treatment groups: 1) a nonimplanted control; 2) a single estrogenic implant, containing 20 mg of estradiol benzoate and 200 mg of progesterone; 3) a single androgenic implant, containing 140 mg of trenbolone acetate; or 4) a single combination implant, containing 24 mg of 17-beta estradiol and 120 mg of trenbolone acetate. Following implantation, the steers were fed a high-concentrate finishing diet for a period of 112 d. Compared with control steers, implanted steers had higher (P < .05) average daily gains and heavier (P < .05) finished live weights and carcass weights. However, there were no differences (P > .05) among treatment groups with respect to their effects on growth rate, live weight, carcass weight, dressing percentage, fat thickness, Longissimus muscle area, percentage of kidney, pelvic, and heart fat, or USDA yield grade. Moreover, marbling scores for implanted steers were not statistically different from marbling scores for control steers. However, a comparison among implant types showed that steers implanted with the estrogenic implant had significantly lower marbling scores than did steers implanted with the androgenic or combination implants. Use of androgenic and combination implants had no effect (P > .05) on beef tenderness of strip loin, top sirloin, or top round steaks; however, use of estrogenic implants decreased (P < .05) tenderness of top sirloin steaks.