To continue to improve genetic predictions is one of the main goals of the IGS genetic evaluation. Over the last year, several updates to models used in the weekly genetic evaluation have been investigated to be incorporated into the weekly genetic evaluation. As the IGS genetic evaluation has grown and expanded from historical partners, as well as the addition of new partners, the ability to run genetic evaluations within a week’s time frame has become difficult. One of the main goals of these updates was to increase the efficiency of evaluations; however, these upgrades are also to maintain or improve the accuracy of prediction of each evaluation. Within the evaluation there are three evaluations that will undergo updates.

The first analysis that will undergo updates is the growth evaluation. The growth evaluation produces EPD for Birth Weight, Weaning Weight, Yearling Weight, Average Daily Gain, Milk, and Maternal Weaning Weight. The changes that will be implemented are updates to the way that breed and years are incorporated into the genetic evaluation, and the method used to incorporate information from other genetic evaluations. Previously, breeds and years were incorporated by fitting interactions of these effects for each animal; with the updates, these effects will be separated. For the incorporation of information from outside genetic evaluations, IGS will use a new method that allows for better tracking of the changes that occur to EPD when this information is added to the evaluation.

The second analysis that will undergo updates will be the Carcass Weight and Ribeye Genetic evaluation. The CW/REA updates will include those described above for the growth evaluation as well as updated across-breed adjustments from the U.S. Meat Animal Research Center (USMARC) GPE program. This program helps to determine breed differences and is an important part of the carcass evaluations at IGS. These updated breed differences will also be applied in the Marbling and Backfat genetic evaluations, which is the third evaluation that will see updates. The updated across-breed adjustments from USMARC is the only change to the Marbling and Backfat evaluation.

Results of the Updates to Genetic Evaluations

When implementing updates to genetic evaluation, the IGS team undergoes a strict validation procedure to evaluate how potential changes will influence the predictive ability of the updated EPD. One of the most common ways this is done is by excluding a portion of the phenotypes, running an evaluation, and correlating the EPD from this run with the excluded phenotypes. For each of the evaluations, all animals that were born after 1/1/2020 were removed from the evaluation and used to test the predictive ability. The results for these comparisons are included in the table below.

         The results in the table above show that the implemented updates had the same or higher correlations than the previously implemented models. This would correspond — in most cases — to more accurate EPD for each of the traits. With the updates, some breeders may notice that the resulting EPD for animals may change, but the percentile rank for the trait may be similar. This is due to differences in estimated breed effects as part of the evaluation. While most traits will have strong EPD correlations between the previous and current evaluation, there will still be some re-ranking of animals because of these updates.

To help breeders see the results of the changes, a list of high-accuracy sires has been put together and is available below.  Based on member and IGS-partner feedback 2 additional updates were tested, validated and implemented. An updated base-adjustment and small change in how external EPD are incorporated were updated. IGS plans to fully shift to the updated growth and carcass models for an EPD release for the week of December 11th.

by Randie Culbertson, PhD
Carcass records on terminal cattle remain rare and highly sought-after phenotypes for National Cattle Evaluation. As the number of carcass phenotypes are limited in the National Cattle Evaluation, IGS uses breed effects from the USDA Meat Animal Research Center to adjust genetic predictions for various breeds. Programs like the Carcass Merit Program and Carcass Expansion Program are adding valuable terminal records and genomic information to the genetic evaluation.

As with any trait under selection, breed effects will change over time. As a result, US-MARC updates their breed effects annually and the IGS Multi-breed Genetic Evaluation recently updated the breed effects in the published EPDs (as of 12/20/21). The implementation of these updated breed effects caused some changes in carcass EPDs. The adjustments are set to an Angus base and are applied depending on the breed percent of the animal. When comparing the rank of bulls with a high percent of a breed, breeders may see a shift in the EPD value but the bulls still have the same rank among other bulls with the same breed percentage. However, reranking occured when comparing one breed to another as well as different percentage composites.

An ongoing challenge of estimating carcass EPDs is the lack of carcass phenotypes. This lack of phenotypes creates a real challenge for the genetic evaluation to appropriately account for breed differences. With traits that have limited records and breed comparisons within contemporary groups, using field data (i.e. IGS data) can lead to unreliable estimation of breed effects. In those cases, breed effects from scientific literature are often used. The advantage of using breed effects from literature is that the effects are derived from “clean” data and often from herds with breeding systems designed specifically to obtain these breed effects. In the case of carcass trait breed differences, the IGS Multi-breed Genetic Evaluation uses the breed effects derived from US-MARC.