Diets consisting primarily of concentrates or of concentrates plus silage in a totalmixed ration (TMR) or discrete ingredient format were compared for effects on beefproduction traits and on beef quality. Sixty continental cross heifers (377 kg, s.d. 31)were allocated to one of the following feeding regimens for 96 days pre-slaughter: (i) a control ration of grass silage, maize silage, a cereal-based concentrate and straw at proportionately, 0.23, 0.15, 0.59 and 0.03 of dietary dry matter, respectively; (ii) a total mixed ration (TMR) with the same dietary ingredients as the control ration; (iii) a high concentrate ration (HC) of a cereal-based diet and straw at proportionately 0.95 and 0.05 of dietary dry matter, respectively. Subcutaneous fat samples were taken from all animals at slaughter and the strip-loin was excised from 10 animals per group forcolour, texture and fatty acid determination. The HC and TMR groups had higher (P < 0.05) daily live-weight gain, slaughter weight and carcass weight than the control group. Muscle protein was highest (P < 0.01) in the TMR group while muscle marbling was highest (P < 0.01) in the HC group. Subcutaneous fat from the HC groupwas less (P < 0.001) yellow than fat from the other groups. Fatty acid analysis of intramuscular fat showed that the HC group had higher C18:1 and lower C18:3 proportionsthan the control group (P < 0.05). The n-6:n-3 fatty acid ratio of intramuscular fatfrom the HC group was higher (P < 0.05) than that of the other groups. The resultssuggest that, at similar feed intakes, TMR feeding offers advantages for beef production over feeding ingredients separately, and yields muscle with a higher protein concentration, while high concentrate feeding yields whiter subcutaneous fat and intramuscular fat with a less nutritionally favourable n-6:n-3 fatty acid ratio.
IJAFR, volume 43, 2004
Irish Journal of Agricultural & Food Research