Wayne R. Wagner and Phillip I. Osborne
Extension Livestock Specialists December, 1997
Federal grading of beef carcasses is a voluntary program, administered by U.S. Department of Agriculture, in which packers may participate at a fee that pays for the service. The official grade consists of a quality and/or yield grade. It is not mandatory that a carcass be yield graded if it is quality graded. These grades are used to divide beef carcasses into uniform groups so the product can be easily described and understand by both buyers and sellers.
Quality grades in young cattle are intended to identify differences in palatability or eating satisfaction of the product. Quality grades are primarily determined by age (estimated maturity of the carcass) and intramuscular fat (marbling). Cattle are classified into maturity groups A through E, with "A" maturity cattle defined as those less than 30 months of age and "B" maturity defined as those from 30-42 months of age. It is only these two maturity groups that are eligible to be graded Prime, Choice, Select or Standard and the relationship between maturity, marbling, and grade is shown in Figure 1.
Figure 1: U.S. Quality Grades a
a As of 1/31/97.
Marbling is visually evaluated by a USDA grader. Figure 1 shows the minimum amount of marbling required for each grade. Marbling scores (or estimated amounts) are described (from least to most) as follows: Devoid, Practically Devoid, Traces, Slight, Small, Modest, Moderate, Slightly Abundant, Moderately Abundant, and Abundant. The minimum marbling requirements for Prime, Choice and Select carcasses with "A" maturity are Slightly Abundant, Small, and Slight respectively.
The relationship between marbling score and percent intramuscular fat is shown in Table 1. When marbling is evaluated in live animals by ultrasound, it is reported as percent intramuscular fat. However, it is important to remember that bulls at the same external fat thickness are likely to have less intramuscular fat than they would have had they been a steer. Although marbling is not very highly related to tenderness, it is associated with juiciness and flavor. Therefore, even if instruments to measure tenderness are perfected to the extent that they can be utilized in grading, marbling is likely to remain an important component of the USDA grade standards.
Table 1: Relationship Between Marbling Score, Intramuscular Fat, and Quality Grade a
Quality Grade b
|Slightly Abundant||8.96 / .5||Low Prime|
|Moderate||7.14 / .2||High Choice|
|Modest||7.02 / .15||Average Choice|
|Small||5.21 / .1||Low Choice|
|Slight||3.76 / .1||Select|
|Traces||2.54 / .2||Standard|
a Iowa State University. 1996 Beef Research Report (AS632).
b "A" Maturity
A common belief has been that the amount of external fat is related to the amount of internal fat or marbling. In other words, in order to increase the amount of marbling, one could feed the cattle longer and put more external finish on the cattle. However, there is evidence to suggest that age and the amount of external finish do not influence the amount of marbling. Therefore, we should be able to find cattle with a sufficient degree of marbling to qualify for Choice that are also relatively lean (.4 inches backfat). Breeds do differ in their ability to marble, but there is considerable variation within a breed. In most breeds there are at least some cattle that will marble sufficiently well to qualify for the Choice grade.
Yield grades are used to identify carcasses that differ in yield of boneless, closely trimmed retail cuts from the round, loin, rib, and chuck. Four factors determine yield grade: 13th rib fat thickness, ribeye area, hot carcass weight, and percent KPH (kidney, pelvic and heart fat). Of these, fat thickness has the largest effect followed by ribeye area. The formula for calculating yield grade is: 2.5 + (2.5 * fat thickness) + (.2 * %KPH) + (.0038 * hot carcass weight) - (.32 * ribeye area). Yield grades range from 1 through 5. A yield grade 5 carcass would have the lowest cutability and would be characterized as light muscled and/or excessively fat.
Because current yield grades are too broad to clearly define value differences in retail yield, yield grades 2 and 3 have been divided into 2A and 2B and 3A and 3B respectively. Yield grades 2.0 to 2.5 are classified 2A and 2.5 to 3.0 are classified 2B. According to the 1991 National Beef Quality Audit, NBQA, 26.0% of the beef carcasses would have fallen into the 2B yield grade and 22.1% would have fallen into yield grade 3A. Cattle with yield grades 3B, 4 and 5 would have comprised 20% of all cattle. Combining quality grade with yield grade more clearly defines carcass value than when quality grade alone is used.
There are essentially two market types and beef producers should strive to produce cattle in one or the other. Those market types are:
Table 2 shows the ideal slaughter mix versus 1995 actual quality grades. This is based upon both foreign and domestic demand. There is no demand for Standard cattle. Although there is some demand for Prime in the US, most of the demand for Prime is for export. Currently, there is more demand for high quality cattle (upper 2/3rds of Choice and Prime) than the U.S. cattle industry is producing. For example, the ideal mix suggests there is a demand for 21% of our cattle in the upper 2/3rds of the Choice grade and in 1995, only 11.4% of the fed cattle killed would have met those requirements.
Table 2:Ideal Slaughter Mix Versus 1995 Actual Grades for Quality a
|Item||Prime||Upper 2/3rds Choice||Low Choice||Select||Standard|
a Executive Summary - 1995 National Beef Quality Audit.
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