EFFECTS OF DIET, BREED AND SLAUGHTER END-POINT ON GROWTH-PERFORMANCE,CARCASS COMPOSITION AND BEEF QUALITY TRAITS IN LIMOUSIN AND CHAROLAISSTEERS

Ninety-six Charolais and Limousin steers were used to evaluate 75% gra in (whole barley or corn) diets and two slaughter endpoints (7 mm back fat or 568 kg liveweight) in an experiment designed to constrain carca ss weights to under approximately 341 kg yet produce optimal beef qual ity. Each breed was represented by eight progeny from each of six sire s. The trial was terminated after 281 d feeding regardless of individu al steers attaining designated slaughter endpoints. Limited availabili ty of dietary energy in whole-barley diets resulted in decreased (P < 0.01) average daily gain and increased (P < 0.01) dry matter intake, f eed/gain and days on feed for barley- vs, corn-fed cattle. Charolais o utgained (P < 0.05) Limousin but dry matter intake was similar on a g BW0(0.75) basis. Feeding to 568 kg liveweight was associated with high (P < 0.10) ADG and decreased (P < 0.05) feed/gain compared with feedi ng to 7 mm. Corn feeding increased (P < 0.001) carcass weights, fat de position and longissimus muscle area. Lean deposition was greater (P < 0.01) in Limousin than Charolais. Taste panel assessment of tendernes s, flavour and juiciness in longissimus muscle was generally not affec ted (P > 0.10) by diet, breed or slaughter endpoint. Twelve primal rib s from each of Agriculture Canada's marbling classifications (A, AA, A AA) were purchased and processed identically to ribs from the test cat tle. Shear and tenderness scores were similar (P > 0.10) across test c attle 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 flavou r than ribs from the test cattle. While 26% of carcasses from test cat tle graded Canada B1 due to either inadequate finish or marbling, simi lar tenderness and shear scores were probably due to age of test cattl e at slaughter which averaged 481 +/- 45 d plus the fact that all roas ts were aged 7 d prior to freezing.