CARCASS TISSUE YIELD AND DISTRIBUTION IN THREE BIOLOGICAL TYPES OF CATTLE FED GRAIN OR FORAGE-BASED DIETS

One hundred and eighty-nine steers comprising 63 small (S) rotational crossbreds, 66 large (L) rotational crossbreeds and 60 Holsteins (H) were fed either a concentrate diet based on corn silage and high-moisture corn, or a forage diet based on a mixture of corn silage and alfalfa haylage. All steers were fed ad libitum and slaughtered to cover a range in external fatness (0–15 mm subcutaneous fat). Steers were removed from feed 36 h and water 16 h prior to slaughter. The left side of each carcass was separated into depot fat, lean and bone. At the same proportion of subcutaneous fat (63 g/kg carcass), S and L carcasses had greater proportions of carcass lean (P < 0.001), but less fat (P < 0.01) and bone (P < 0.001) than carcasses from H Steers. Small and large carcasses had greater muscle to bone ratios (P < 0.001) than carcasses from H steers. Diet had no effect on lean tissue proportions, but forage feeding increased carcass bone (P < 0.001) and decreased carcass fat (P < 0.01). Forage feeding also resulted in carcasses with lower muscle to bone ratios (P < 0.01) than carcasses produced from grain feeding. Holstein-carcasses had more carcass fat partitioned into the body cavity depot and less into the subcutaneous depot than S and L carcasses, but diet had no effect on fat partitioning. Biological type (S, L or H) and diet were found to have a minor effect on fat distribution. The results are discussed with reference to carcass evaluation of beef and dairy cattle fed diets based on forage or grain. Key words: Biological type, diet, carcass composition, carcass grading