In the life of any National Cattle Evaluation, periodic updates are needed to make the best use of all available information and technology. The evaluation which generates the EPDs published by NALF are no exception. Over the last couple of years, a massive research undertaking has been going on to modernize the evaluation of growth traits (Birth Weight, Weaning Weight, Yearling Weight and Milk). Below, is a brief description of each update followed by the impact of these collective changes on NALF EPD. These changes are expected to be incorporated into the production run generated from IGS on the week of August 17.
The changes made include:
1. A new definition of contemporary groups based on the age of the dam. Calves born to first-calf females will be placed in a separate contemporary group.
2. Setting the genetic correlation between weaning weight maternal (milk) and weaning weight direct to 0 (compared to – 0.3).There has been debate in the scientific literature about the degree and direction of genetic correlations between direct and maternal weaning weight. Previously, the IGS evaluation used a moderate negative correlation. This meant that young, unproven animals with high growth potential often saw negative impact on their milk EPD when their own growth data was submitted or when a genomic test was done. The correlation in the new model will be set to zero. This should impact animals with low accuracies the most.
3. Different variances for different sexes (heterogeneous variance). Bull calves typically have higher growth potential than heifers, which means the variation in their weights is also greater. The new model will account for this difference.
4. New DNA Marker subset. Since BOLT-powered EPDs were released, many more animals have been genotyped, and many more performance records have been submitted. As a result, new, more informative markers were able to be deciphered. The new EPDs will employ this new, larger marker set on the growth traits.
5. Accounting for different birth weight collection methods. Upon closer analysis of birth weight data, it became apparent that different reporting and collection methods were being used. These methods ranged from reporting in 2lb or 5lb increments, to data that was obviously from hoof tapes instead of scales, to clearly fabricated data. New methods allow for the identification and proper accounting for these various collection methods.
6. Not including genomic effects for Weaning Weight Maternal (Milk). The current genetic evaluation marker effects for both WW and Milk. However, in the new evaluation the ability for the genomic part of the EPD calculations for Milk to be performed caused problems with the overall efficiency of the weekly evaluation. Therefore, the decision was made to remove the genomic component for Milk. Even with the removal of this information, work done to judge the efficacy of EPDs, shows that the resulting EPDs from the updated model are an improvement over the previous evaluation.
In the table below, you’ll find a comparison of the genetic trend graph for the current growth suite of EPD vs the genetic trend for the new WO1 suite of growth EPDs that will be released in the next week.
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