Marbling score

Marbling, the flecks of fat in the lean, is the primary factor determining quality grade after maturity has been determined. Marbling is evaluated either visually or using cameras in the ribeye muscle, which is exposed between the 12th and 13th ribs. Marbling score values are used in determine the quality grade of a caracass.

Phenotype

Numerical Scores for USDA Quality Grades and corresponding Marbling Scores*
Quality Grade	Marbling	Score
Prime	Abundant	9.0 – 9.9
Prime	Moderately Abundant	8.0 – 8.9
Prime	Slightly Abundant	7.0 – 7.9
Choice	Moderate	6.0 – 6.9
Choice	Modest	5.0 – 5.9
Choice	Small	4.0 – 4.9
Select	Slight	3.0 – 3.9
Standard	Traces	2.0 – 2.9
Standard	Practically devoid	1.0 – 1.9

*These values were changed on February 7, 2022 to correspond with the numeric scores used by USDA.

Relationships between marbling scores and intramuscular fat percentages are shown below:

Marbling and Intramuscular Fat
Marbling Score	Intramuscular Fat, %
Slightly Abundant	10.13
Moderate	7.25
Modest	6.72
Small	5.04
Slight	3.83
Traces	2.76

Adjusted Value

Marbling score is then reported on an age-constant basis.

Contemporary Group

A contemporary group is a set of cattle of the same sex that have been raised together and have received equal treatment up to the point of slaughter. All progeny within a contemporary group should ideally be born within a 90-day period, and male calves must be castrated. A contemporary group up to the time of weaning will be subdivided if some cattle go on feed as calves and others are started on feed as yearlings, and if the cattle are then split into two or more slaughter groups. Birth date, identification of sire and dam, breed of dam (or breed proportions in crossbred dams) should be recorded for all individuals.

Genetic Evaluation

Marbling score is generally included in a multiple-trait model along with its ultrasound indicator and other carcass-fat-related traits (e.g., back fat and ultrasound back fat). An early growth trait (e.g., birth or weaning weight) may also be included to account for sequential culling if the genetic covariance is sufficient. Only direct genetic effects are fitted.

Usage

Although producers are paid for improved quality grade, marbling score is generally considered an economically relevant trait. Producers can use marbling score EPD to improve the quality grade of fed cattle. Ideally this would be done through the use of a more comprehensive economic selection index that takes into account other revenue traits as well as traits related to the cost of production.