Abstract
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<0.01) average daily
gain and increased (P<0.01) dry matter intake, feed/gain and
days on feed for barley- vs. corn-fed cattle. Charolais outgained
(P<0.05) Limousin but dry matter intake was similar on a g
BW0.75 basis. Feeding to 568 kg liveweight was associated
with high (P<0.10) ADG and decreased (P<0.05) feed/gain
compared with feeding to 7 mm. Corn feeding increased (P<0.001)
carcass weights, fat deposition and longissimus muscle area.
Lean deposition was greater (P<0.01) in Limousin than Charolais.
Taste panel assessment of tenderness, flavour and juiciness
in longissimus muscle was generally not affected (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.
1Food Science, University of Guelph
2Mathematics and Statistics, University of Guelph
3Ridgetown College of Agricultural Technology