Body Composition Evaluation
This paper presents the relationships found and developed into a set of regression formulas for marbling score (MS) and actual percentage intramuscular fat (PIMF) using data from realtime ultrasound (RTU) certification programs. MS was determined to the nearest 10th of a marbling degree by a USDA grader—that is, sm10, sm20, etc. The same USDA grader was used each year. Percentage intramuscular fat was determined by removing a 1/4 in. facing from the 12th rib. This facing was returned to the Iowa State University Meat Laboratory, trimmed so that the sample contained only the longissimus dorsi muscle, freeze-ground, and sub-sampled. Product moment correlations between PIMF and MS were .95, .82, and .89 for 1996, 1997 and combined years, respectively. The results shown in this paper are not characteristic of what is generally observed in the industry. However, it shows that there can be a high correlation between the subjective grading of marbling as compared to actual chemical fat in the longissimus dorsi muscle. The USDA grader that graded these cattle knew he was being compared to an instrument grading system. How much fairer might the current grading system be if this technology were to be embraced and implemented by the beef packing industry?
Iowa State University
Wilson, Doyle E.; Rouse, Gene H.; and Greiner, Scott, "Relationship Between Chemical Percentage Intramuscular Fat and USDA Marbling Score" (1999). Beef Research Report, 1998. 1.