CANADIAN, AMERICAN, AND JAPANESE CARCASS GRADES OF HEIFERS FED TO HEAVY WEIGHTS TO ENHANCE MARBLING

Yield and quality grades were measured in two studies evaluating commo n breeds (Angus, Hereford, Hereford x Angus and Holstein) and nutritio n programs for production of highly marbled beef for the Japanese mark et. Weaned heifer calves (n = 221, initial weight 265 kg) were slaught ered at 500, 590, and 680 kg in exp. 1. In exp. 2, yearling heifers (n = 216, initial weight 395 kg) were slaughtered at 590 and 680 kg. Cat tle were assigned to either a high plane of nutrition (HP) until slaug hter or to a moderate plane of nutrition until 500 kg (exp. 1) or 550 kg (exp. 2), followed by HP to slaughter (MHP). Carcasses were graded at the Japanese (6/7th rib) and Canadian/US (12/13th rib) grading site s. Extended feeding of heifers from the three beef breeds for 199 to 4 74 d and to slaughter weights up to 680 kg enhanced marbling at the co st of very poor USDA and Canada yield grades (extremely fat carcasses) . Most carcasses had sufficient marbling to qualify for Canada AAA or USDA Choice quality grades, but only achieved average Japanese quality grades. Carcasses were frequently downgraded by the Japanese grading system because of coarse marbling texture, poor fat texture, and soft or coarse muscle texture, especially at the higher slaughter weights. Compared with the beef breeds, Holsteins produced leaner carcasses wit h at least as much marbling, and had superior Japanese quality grades, similar Japanese yield grades, and superior Canadian and US yield gra des. However, carcasses with dairy conformation may be subjectively do wngraded by grading systems in most countries, including Japan. Feedin g early-maturing cattle high grain diets to excessive slaughter weight s was not effective in producing beef with sufficient marbling to achi eve the highest Japanese (5) or US (Prime) quality grades, but produce d carcasses that were too fat for North American markets.