Sustained growth promotion, carcass and meat quality of steers slaughteredat three liveweights

The experiment measured the effect of a sustained growth promotion strategy on growth rate, carcass characteristics, and meat quality of Brahman and F -1 Brahman crossbred steers. Meat quality was assessed objectively by labor atory measurement and a subset of samples evaluated subjectively by consume r taste panels. Steers were allocated to one of 12 treatment groups; 2 impl ant strategies x 3 liveweights at slaughter x 2 nutritional finishing strat egies. The 2 implant strategies were unimplanted controls and implantation with 20 mg oestradiol-17 beta (Compudose) every 100 days. The target carcas s weights at slaughter were about 220 kg (Australian domestic market), abou t 280 kg (Korean market) and about 320 kg (Japanese market). Steers were fi nished either at pasture or on a grain-based diet in a feedlot. For every treatment group except where steers were finished in a feedlot fo r the domestic market, the implant strategy resulted in significantly (P<0. 01) heavier final liveweights, significantly (P<0.01) greater cumulative li veweight gains and significantly (P<0.05) heavier carcass weights. The magn itudes of the significant liveweight responses ranged from 30 kg for pastur e fed steers for the domestic market to 47 kg for pasture fed steers for th e heavier weight Japanese market. Repeated treatment with oestradiol-17<beta> had no significant effect on ca rcass composition as determined by indices of carcass lean and carcass fat. The additional yield of retail beef from implanted steers was principally associated with increased carcass weight. The magnitude of the increase in beef yield was 8 kg (n.s.) for domestic, feedlot steers; 15 kg (P<0.01) for Korean, feedlot steers and 18 kg (P<0.001) for Japanese, feedlot steers. In steers finished in the feedlot for the Korean and Japanese markets, sust ained growth promotion was associated with a significant (P<0.01) decrease in meat tenderness as measured by peak force. In contrast there was no such effect in other groups measured (domestic market, feedlot finished and Jap anese market, pasture finished). Consumer assessment of eating quality was conducted on steaks from steers, finished in a feedlot for the Korean and J apanese markets. At both slaughter weights there was no significant effect of treatment on tenderness, juiciness, flavour, overall acceptability or me at quality score which combined tenderness, juiciness, flavour and overall quality. However, mean preference scores from implanted steers were consist ently lower than those from control steers. It was concluded that the aggressive implant strategy resulted in substanti al increases in weight gain that were more pronounced during periods of mod erate growth rate relative to periods of very low rates of gain. During per iods of low weight gains or weight stasis there was little advantage from i mplantation. Carcass composition was not significantly modified by treatmen t with oestradiol. The effect of the aggressive implantation strategy on ea ting quality of the beef was equivocal and further investigation is certain ly warranted.