USDA beef quality grades assigned to beef carcasses indicate the tenderness, juiciness and flavor of cooked beef. Beef quality grades are based on the degree of marbling a USDA grader finds in the rib-eye muscle of a ribbed carcass between the 12th and 13th ribs and the maturity of the carcass.
The “A” maturity designation means that a hanging beef carcass shows a degree of maturity between 9-30 months of age. Accordingly, if you send lighter calves or long yearlings to the feedyard, after the typical finishing phase of at least 150 days of a high-energy, corn-based ration fed ad-lib, they should yield an “A” maturity carcass. Because of this, marbling score is the primary factor that determines quality grades in “A” maturity beef carcasses.
In conventional beef production, cattle are fed for an amount of time to reach a compositional endpoint with the objective of tapping their full genetic potential to grow and develop marbling. Marbling is one type of fat we find in the carcass (external fat, seam fat, and kidney, heart and pelvic fat).
Marbling is commonly referred to as intramuscular fat because of where it is found within the rib-eye muscle. As such, marbling can’t be seen in live animals. Therefore, the compositional endpoint to which cattle are fed is based on external finish. Because of its location in the beef carcass, marbling has more influence on the tenderness, juiciness and flavor of cooked beef than the other types of fat.
As a result, marbling and beef quality grades are typically the biggest driver of beef carcass value. From highest to lowest, the four quality grades that exist for “A” maturity beef carcasses are Prime, Choice, Select and Standard.
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The chart shows how marbling scores down the left hand column relate to beef quality grades. Three marbling scores are shown beside the Prime and Choice quality grades, permitting the grades to be split into thirds. For example, moderate and modest marbling scores are connected to the upper two-thirds of the Choice grade, which is a specification threshold for carcasses to be certified for quality-based premium branded programs like Certified Angus Beef.
When beef carcasses fall into the “B,” “C,” “D” and “E” maturity groups, lower quality grades are assigned, and there is no longer potential for the best quality grades.
Beyond marbling and maturity, the amount of time on feed, the genetic potential and the breed type of beef cattle play a big role in the quality grades achieved. Marbling is one of the later-maturing fat types to develop. A wide range of genetic propensity to grow and develop marbling relative to other types of fat exists within and between different beef breeds. — Mark Z. Johnson, Oklahoma State University Extension beef cattle breeding specialist
