Genetic Markers and Their Use in Feedlot Cattle

Steve Boyles, OSU Extension Beef Specialist

Carcass characteristics are economically important but can be difficult to measure pre-harvest. Therefore, genetic markers associated with these traits may provide valuable information to decision makers. The success of genetic markers depends on the accuracy of molecular breeding values (MBV). Researchers at Oklahoma State University evaluated molecular breeding values for yield and quality grades for commercial beef cattle and reported it in their publication:

Yield and quality grade outcomes as affected by molecular breeding values for commercial beef cattle.
N. M. Thompson, E. A. DeVuyst, B. W. Brorsen, and J. L. Lusk.
J. Anim. Sci. 2015.93:2045–2055

Independent validations report significant correlations between molecular breeding values and the traits they predict. However, many of these molecular breeding values explain less than 50% of genetic variation. For example, a test that explains 50% of genetic variation and has a heritability of 0.4 explains just 20% of what we observe in the trait.

A gene marker panel score for marbling of 8 out of 10 indicates relatively high genetic potential for marbling. However, there still exists a lack of practical information about how these values translate into the likelihood of on-the-hoof or on-the-rail outcomes. That is, given a gene marker panel score for marbling of 8, what is the probability that an animal will grade Choice or better?

About 9000 head of commercially fed cattle and a subsample of 4700 black- hided cattle were evaluated for genetic markers for yield grade and marbling. The data was from 6 different Midwestern feed yards provided by Neogen, the parent company of Igenity. At arrival a hair sample or tissue punch from ear tag application was collected for genetic testing.

Panel scores are Igenity’s method of communicating molecular breeding values to a commercial audience. Kind of like the stars you may see in some bull sale catalogues. Igenity panel scores report genetic potential for a given trait as a single score, ranging from 1 to 10. Animals with panel scores of 1-2- 3 were characterized as having “low” genetic potential; 4-5-6-7 were “moderate”; and 8-9-10 were “high” genetic potential. One clarification is that a high genetic potential/panel score for yield grade should lead to a lower, more favorable yield grade.

The majority of the cattle were graded USDA yield grade 2 (44%) or 3 (37%) and quality grade Select (42%) or Low Choice (42%).

Black-hided bos taurus steers with “low” genetic potential for yield grade and marbling had about a 29% chance of achieving the base price or better on a price grid (yield grade 3 or lower and quality grade Low Choice or better). An animal with “moderate” genetic potential for both yield grade and marbling had a 46% chance of achieving the base price or better on a price grid, and animal with the highest scores had a 66% chance of achieving this same outcome.

Higher genetic potential for yield grade resulted in less favorable quality grade outcomes. However, this effect was diminished the longer the animal was on feed. Higher genetic potential for marbling led to less favorable yield grade outcomes. The tradeoff between yield grade and quality grade outcomes may be more exaggerated among black-hided steers than for the general population.

Increasing the yield grade marker from minimum to the maximum decreased the probability of receiving yield grade discounts by half, from 14 to only 7% for the general population and from 19 to 9% for black-hided steers.

In general, distributions of yield grade outcomes for the general population and black-hided bos taurus steers were similar. The only notable difference was that black-hided bos taurus steers were more likely to grade yield grades 3, 4, and 5, and less likely to grade yield grades 1 and 2 regardless of the level of genetic potential for yield grade.

Increasing genetic potential/panel scores for marbling led to more favorable quality grades. Steers with the lowest score for marbling had a probability of grading Standard or Select 73% of the time for the general population and 71% for black-hided bos taurus steers. However, this probability dropped to just 20% for the general population and 21% for black-hided bos taurus steers when genetic potential for marbling was increased to the maximum observed value.