Effects of diet, breed and slaughter endpoint on growth performance, carcass composition and beef quality traits in Limousin and Charolais steers

Ninety-six Charolais and Limousin steers were used to evaluate 75% grain (whole barley or corn) diets and two slaughter endpoints (7 mm backfat or 568 kg liveweight) in an experiment designed to constrain carcass weights to under approximately 341 kg yet produce optimal beef quality. Each breed was represented by eight progeny from each of six sires. The trial was terminated after 281 d feeding regardless of individual steers attaining designated slaughter endpoints. Limited availability of dietary energy in whole-barley diets resulted in decreased (P   0.10) by diet, breed or slaughter endpoint. Twelve primal ribs from each of Agriculture Canada's marbling classifications (A, AA, AAA) were purchased and processed identically to ribs from the test cattle. Shear and tenderness scores were similar (P > 0.10) across test cattle and purchased ribs, despite intramuscular fat contents of 20.2, 27.1, 35.6 and 49.7 g kg −1 respectively, for test cattle and trace, slight and small marbled ribs. Slight and small marbled ribs did have higher (P < 0.05) taste panel scores for initial juiciness and flavour than ribs from the test cattle. While 26% of carcasses from test cattle graded Canada B1 due to either inadequate finish or marbling, similar tenderness and shear scores were probably due to age of test cattle at slaughter which averaged 481 ± 45 d plus the fact that all roasts were aged 7 d prior to freezing. Key words: Charolais, Limousin, marbling, fatness, palatability, carcass weight, beef cattle, tenderness