Effects of hormonal growth promotant (HGP) implantation on liveweight, carcass and meat quality measurements were examined using 80 Angus yearling cattle. After entry to the feedlot, 40 steers and 40 heifers were implanted with Revalor-S (28 mg oestradiol and 140 mg trenbolone acetate) and Revalor-H (20 mg oestradiol, 200 mg trenbolone acetate), respectively. Cattle were slaughtered after 55 and 65 days on feed. Samples from the Mm. longissimus dorsi, biceps femoris (the cap and body portions), gluteus medius (the eye and D portions), infraspinatus and triceps brachii were prepared for sensory testing after aging for 5 and 21 days after slaughter. A total of 854 muscle samples were cooked by grill (601) or roast (253) methods and served to consumers using the Meat Standards Australia taste panel protocols.

When adjusted to the same initial liveweight, implantation with Revalor-H and Revalor-S resulted in a 4 and 7% increase in slaughter weight, respectively. Implantation resulted in an increased ossification score in steers (P < 0.05), but not in heifers. There was a significant interaction (P < 0.05) between HGP implantation and days aged for shear force. There was a small effect of HGP implants on compression (P < 0.05), but not on cook loss and intramuscular fat percentage. Muscles differed in their response to HGP implantation (P < 0.05) for tenderness, overall liking and palatability scores. Muscles also differed in their aging rates after slaughter (P < 0.05). The greatest response in sensory scores to HGP implantation was found in those muscles that had the highest aging rates. Possible mechanisms by which muscles differed in their response to HGP implantation are discussed.