The test provides a GMX Score, from one to 100, which combines the animal’s genetic potential for marbling and gain, along with a separate percentile-based value of one to five for each of the two traits.
Producers can use the test to select replacement heifers based on their potential to produce high-value calves that gain and well, or to test feeder calves to provide genomic-based scores to use as a marketing tool. In the long run, CAB sees the test and resulting selection as a means to increase supplies of cattle qualifying for the premium-beef program.
After the genomic test GeneMax™ (GMX) was introduced in early 2012, Angus producers set about using it. Many saw a marketing advantage for sorting and selling cattle with a genomic profile for gain and grade potential. Others set about using the technology to top up female quality in their own herds, while selling the steer half of progeny based those average GMX scores.
Recently, CAB conducted a field trial in Kansas to evaluate how well the GMX scores correlated with actual feedyard performance and carcass value in Angus steers. Gary Fike, a beef cattle specialist for CAB, presented results of the trial at the Midwest Section of Animal Society of Animal Science in Des Moines, Iowa.
The trial used 173 Angus steers from one Kansas ranch fed in two pens at Pratt Feeders in Kansas, and harvested when they had a visually estimated half-inch of external fat on two sorting dates at a Dodge City, Kan., packing plant.
The researchers recorded average daily gains and marbling scores on the cattle, all of which had been DNA tested and rated for GMX scores of high, mid-high, mid-low or low. As shown in the tables below, actual marbling scores and actual average daily gains matched up well with the levels predicted by the GMX scores for each trait. The cattle with high GMX marbling ratings produced actual marbling scores averaging 538, well above the 500 cutoff for middle Choice Quality grade and qualification for CAB. Cattle with mid-high GMX marbling scores produced actual marbling scores of 518, while those rated mid-low or low produced actual marbling scores of 479 and 466 respectively.
As for average daily gains, those with the high or mid-high GMX scores averaged 4.33 pounds and 4.35 pounds respectively, while those with the mid-low and low GMX scores gained 4.27 and 4.22 pounds per day respectively.
Among steers with the high GMX scores, CAB acceptance rate was 69.9 percent, while acceptance among those with low GMX scores was just 28.6 percent. Average carcass value for those with the high GMX scores was $1,924, compared with $1,894 for those with low GMX scores.
Read a more detailed summary of the field trial.
Table 1 - Marbling Score and Average Daily Gain by GMX Score Groups
| GMX Score Group | No. head | Feedlot In-Weight, lb. | Days on Feed | Avg. GMX Score | Avg. GMXMarbling | Marbling Score* | Avg. GMXGain Score | Average Daily Gain** |
| High | 83 | 811.5a | 142.0 | 90 | 4.52a | 538a | 4.64a | 4.33 |
| Mid-High | 32 | 827.5ab | 142.0 | 70 | 3.19b | 518ab | 4.06b | 4.36 |
| Mid-Low | 30 | 854.1b | 143.9 | 52 | 2.63b | 479b | 3.53b | 4.27 |
| Low | 28 | 838.9ab | 143.2 | 25 | 1.61c | 466b | 2.86c | 4.22 |
Table 2 - Carcass measurements, CAB acceptance and dollar values by GMX Score Groups
| GMX Score Group | HCW, lb. | Rib Fat, inches | REA, sq. inches | Calc. YG | % CAB Acceptance | Odds Ratioa | Carcass Value (per head) |
| High | 915.1 | 0.52 | 14.44a | 3.41 | 69.88 | 4.96 | $ 1923.94 |
| Mid-High | 915.4 | 0.52 | 14.63ab | 3.55 | 65.63 | 4.62 | $ 1926.42 |
| Mid-Low | 910.8 | 0.48 | 15.21b | 3.22 | 43.33 | 2.35 | $ 1893.21 |
| Low | 908.8 | 0.47 | 14.90ab | 3.23 | 28.57 | 1.00 | $ 1894.07 |
Read more:
http://www.cattlenetwork.com/cattle-news/Trial-illustrates-accuracy-of-genomic-predictions-231493961.html?view=all
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