Evaluating Genetic Evaluations by Carcass End Point

Most genetic evaluations for carcass traits adjust to an age-constant end point; however, cattlemen typically harvest their cattle according to a fat, carcass weight or quality grade end point, observed Janice Rumph, assistant professor in the department of animal and range sciences at Montana State University, Bozeman. But does that mean we’re wrong?

During the Selection Decisions roundtable discussion at the 35th Annual Beef Improvement Federation (BIF) Meeting, Rumph presented research she is conducting for the American Simmental Association to answer that question. The roundtable was held at the BIF Meeting May 29, 2003, in Lexington, Ky.

Using the age-constant end point is not wrong if either (1) we harvest at an age-constant end point or (2) it doesn’t re-rank sires compared to how they would rank according to actual harvest end points, Rumph said. Her research evaluated a database of more than 16,000 animals to compare correlations of using four different end points — age, carcass weight, marbling and fat thickness. Other traits evaluated included ribeye area and percent retail cuts.

Most of the correlations for fat thickness, carcass weight, marbling and ribeye area when adjusted to a carcass weight or a fat end point compared to an age end point fell within the 0.86 to 0.95 range. While there were a few bulls that were re-ranked for the traits, most of the ranks held constant.

Percent retail cuts, however, was a different story. The rank correlation was only 0.60 for fat-adjusted scale vs. the age-constant scale. The top 10 bulls for percent retail cuts when ranked on the age-adjusted were dramatically re-ranked when adjusted to a fat constant end point (see table and Rumph’s Power Point presentation), Rumph reported as an example.

Ranking of sires for percent retail cuts by
end point used for genetic evaluation
Age Adj. CWT adj.a Marb adj.b Fat adj.c
1 1 220 22
2 2 4 2
3 14 639 517
4 6 5 104
5 4 3 6
6 3 6 59
7 7 2 8
8 5 1 288
9 10 53 269
10 9 11 169

a0.96 correlation with age-constant end point.
b0.88 correlation with age-constant end point.
c0.60 correlation with age-constant end point.

In summary, Rumph said, changing the carcass end point does alter bull rankings. That leaves three options: (1) use different end points for different expected progeny differences (EPDs); (2) change all EPDs to a different end point; or (3) do nothing. The research is a work in progress, she said. More work needs to be done before deciding upon the best option.

To access Rumph’s Power Point presentation, visit the newsroom.

— by Shauna Rose Hermel