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

Abstract

The experiment measured the effect of a sustained growth promotion strategy on growth rate, carcass characteristics, and meat quality of Brahman and F1 Brahman crossbred steers. Meat quality was assessed objectively by laboratory measurement and a subset of samples evaluated subjectively by consumer taste panels. Steers were allocated to one of 12 treatment groups; 2 implant strategies x 3 liveweights at slaughter x 2 nutritional finishing strategies. The 2 implant strategies were unimplanted controls and implantation with 20 mg oestradiol-17β (Compudose) every 100 days. The target carcass weights at slaughter were about 220 kg (Australian domestic market), about 280 kg (Korean market) and about 320 kg (Japanese market). Steers were finished either at pasture or on a grain-based diet in a feedlot. For every treatment group except where steers were finished in a feedlot for the domestic market, the implant strategy resulted in significantly (P<0.01) heavier final liveweights, significantly (P<0.01) greater cumulative liveweight gains and significantly (P<0.05) heavier carcass weights. The magnitudes of the significant liveweight responses ranged from 30 kg for pasture fed steers for the domestic market to 47 kg for pasture fed steers for the heavier weight Japanese market. Repeated treatment with oestradiol-17β had no significant effect on carcass 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, sustained 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 Japanese market, pasture finished). Consumer assessment of eating quality was conducted on steaks from steers, finished in a feedlot for the Korean and Japanese markets. At both slaughter weights there was no significant effect of treatment on tenderness, juiciness, flavour, overall acceptability or meat quality score which combined tenderness, juiciness, flavour and overall quality. However, mean preference scores from implanted steers were consistently lower than those from control steers. It was concluded that the aggressive implant strategy resulted in substantial increases in weight gain that were more pronounced during periods of moderate growth rate relative to periods of very low rates of gain. During periods of low weight gains or weight stasis there was little advantage from implantation. Carcass composition was not significantly modified by treatment with oestradiol. The effect of the aggressive implantation strategy on eating quality of the beef was equivocal and further investigation is certainly warranted.