Although ribeye area is not a yield grade factor, ribeye size is important in evaluating the carcass merit of a lamb. Only the large major ribeye muscle should be measured - do not count the small muscles adjacent to the ribeye muscle. Both ribeye muscles should be measured and the average reported. Quality Grades Quality grades indicate the expected eating satisfaction of lamb. USDA Lamb Quality Grades are based upon palatability indicating characteristics of the lean and carcass conformation.
Conformation has no direct influence upon the eating quality.
For quality grading purposes, there are three carcass classes - lamb, yearling mutton and mutton. There are four quality grades within each class. For lamb and yearling mutton the quality grades are Prime, Choice, Good and Utility. Mutton carcasses are graded Choice, Good, Utility and Cull. The cannon bone on the left exhibits the typical break joint.