Interpretation of Marbling Scores in Selection of Young Beef Bulls

Two of the measures on young beef bulls coming off the 112 day Beef Improvement Ontario test program are intramuscular fat percent (IMF%) and estimated Grade.

Intramuscular fat percent (Marbling) is predicted by using image analysis techniques designed to differentiate between fat and lean in the Real Time Ultrasound image taken at the 12^th and 13^th rib. Relationship between marbling scores (grade) and intramuscular percent fat are shown below:

Marbling and Intramuscular Fat^z

z - Guidelines for Uniform Beef Improvement Programs, BIF, 1996
y - minimum level of Intramuscular Fat to meet Marbling Score criteria

Intramuscular fat percent (IMF%) is determined from the ultrasound image, and to allow comparisons between bulls, adjusted to 365 days of age. An estimated grade is then determined based on the table above. The ultrasound measurement provides producers with an insight into carcass information previously available only with an actual carcass measurement or a progeny test. The exact genetic relationship between ultrasound measurements taken on yearling bulls and actual progeny carcass data of steers or heifers is still unclear. However, producers selecting bulls can utilize this information as an indication of the individual bulls ability to marble and grade at 365 days of age, with the awareness that carcass traits are moderately to highly heritable and the individual results will be reflected in progeny performance to some extent.

Researchers at Iowa State University are currently analyzing data to determine the relationship between carcass and ultrasound measurements of intramuscular fat percent. The preliminary genetic correlations indicate that carcass intramuscular fat percent, ultrasound predicted intramuscular fat percent and visual marbling assessment are expressions of similar genes. Therefore, researchers suggest that ultrasound predicted intramuscular fat percent can be used to classify sires as low or high for actual intramuscular fat percent.

Intramuscular fat percent is one of many available traits to use in sire selection but appropriate emphasis should be placed on other traits which contribute to the efficiency and ultimately profitability of the cow herd. Once traits are chosen and the list of sires are narrowed down producers can use IMF% to classify the sires and choose according to the genetics of their cow herd and their projected market. Carcass evaluations provide another piece of the puzzle and the ability of producers to categorize the genetics of their calves will give them a competitive edge in future marketing plans and potential alliances with other segments of the industry.

For more information on interpretation of genetic evaluations, contact Beef Improvement Ontario.

Related Links

• Beef Improvement Ontario