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Angus enhances its genetic analysis

Cattle and Beef Industry News
Jul 14, 2017

Cover painting from WLJ's 2013 Bull Guide

The American Angus Association has made a quantum leap forward in its genetic analysis moving to the “One Step” model for the calculation of expected progeny differences (EPDs). This will greatly improve the amount of information garnered from genomics. In addition, Angus has done a regular update in genetic parameters such as trait heritabilities and genetic correlations as well as economic assumptions for their indexes.

Although producers will see changes in EPD and index values and rankings, the new genetic predictions and indexes will be more precise and reliable than those produced in the old two-step analysis. All this adds up to producers being able to make more informed decisions when objectively selecting Angus cattle.

In the old two-step procedure, genetic predictions were calculated much as they have been since the 1980s, which were not built to handle genomics. To get around this, a molecular breeding value was calculated from the genomics and then used as a correlated trait to the traditionally calculated EPDs much as birth weight is correlated to weaning weight.

This process had many drawbacks and did not make full use of the genomic information. With One Step, genomics are incorporated directly into the model, significantly increasing precision and reliability of the genetic predictions. Essentially, One Step incorporates each genomic marker from a panel into the model much as various performance data is, such as a weaning weight.

The new One Step genetic predictions are more precise than the old ones because an exact genetic relationship between animals is calculated from the genomic markers rather than the estimated system used in two step.

For instance, the old twostep procedure started out with the assumption that full siblings had the same genetic contribution from both their sire and dam. This is why parental EPDs could be easily calculated by adding half of the sire’s to half of the dam’s EPDs. In reality, full siblings can be 0-100 percent related. With One Step, the actual genomic relationship can be calculated from the marker panels.

Calculating the actual genomic relationship between animals makes One Step genetic predictions much more precise than the old two-step model. It is akin to calculating a genetic prediction from two different contemporary groups of equal size, but one containing unbiased data and the other biased data. A genetic prediction of the same accuracy will be calculated from each contemporary group, but the prediction from the unbiased data will be closer to the true genetic value.

The same occurs when the genetic relationship is calculated from the markers rather than estimated. By utilizing the genomic relationship between animals rather than estimating it from the pedigree, the genetic predictions are much more precise.

Accuracy is also significantly improved by utilizing all the markers in the model rather than a single correlated molecular breeding value. With One Step, tens of thousands of genomic markers go directly into the calculation of the genetic predictions, greatly adding to the amount of information utilized in their calculation. This is akin to producing an EPD from two contemporary groups with one having significantly more animals in it than the other. Because the EPD from the larger contemporary group is based on more information, it will result in a higher accuracy, more reliable genetic prediction.

One Step is not a new methodology to the livestock industry, and has been used successfully for years in the dairy, swine and poultry industries. The beef industry is late to the game in terms of modernizing its genetic analysis to the era of genomics, relying instead on 30-year-old legacy technology. With One Step, Angus joins smaller breeds like Brangus, Beefmaster, and Santa Gertrudis in implementing a much better approach to the calculation of genetic predictions.

Other changes

Along with implementing One Step, the American Angus Association has also taken this opportunity to improve the estimates of the heritability of various traits as well as the genetic correlation between traits that are used in the genetic prediction models. This is done with all genetic analyses from time to time as databases grow and more information becomes available to calculate more reliable genetic parameters. This means most traits have slightly different heritabilities than before the update, which will result in some change in the genetic predictions.

Genetic correlations are the genetic relationship between traits. For instance, many of the same genes that control weaning weight also control yearling weight. Since this is known, the genetic correlation between the traits is added into models to increase the accuracy of the respective EPDs. Updating the genetic correlations based on the current larger database is highly valuable to producing more precise and reliable genetic predictions and indexes.

The last update the American Angus Association undertook is the economic assumptions used to calculate the indexes, which is done annually. These updates make the indexes more current to recent economic realities, changing the values and rankings accordingly.

All this adds up to a lot of change for Angus breeders and their customers, but doing it all at once has its benefits. In general, people do not like change no matter how positive the change will be in the long run. Angus stakeholders can now get used to these positive changes and the new values and rankings of the genetic predictions and indexes. The alternative would have been a series of changes made piecemeal over time.

The American Angus Association’s move assures members and commercial customers have the most precise and reliable genetic predictions and indexes possible. With regards to the One Step model Angus implemented, it is highly proven in other livestock species, and the beef industry is long overdue in implementing the technology. — Dr. Bob Hough, WLJ correspondent

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