by Dr . Tonya Amen Geneticist for North American Limousin Foundation
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 EPDs .
The changes made include :
1 . 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 set to zero . This should impact animals with low accuracies the most .
2 . 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 accounts for this difference .
3 . New DNA Marker subset . Since BOLT-powered EPDs were released , more animals have been genotyped , and more performance records have been submitted . As a result , new , more informative markers were able to be deciphered . The new EPDs employ this new , larger marker set .
4 . 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 2 lb . or 5 lb . 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 .
5 . Not including genomic effects for Weaning Weight Maternal ( Milk ). Formerly , the genetic evaluation included genomic 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 Work Order 1 suite of growth EPDs that was recently released .
Genetic Trend W01 VS 063020 Production Run
72 • OCTOBER 2020