By Randiie Culbertson, Ph.D. |
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 11/9/20). 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 percentage 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 occurred 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 (see article by Lane Giess about Maximum Carcass Knowledge, page 38). 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.
In addition to updating the US-MARC breed effects, an adjustment to the carcass weight and rib eye evaluation is being tested to allow the inclusion of carcass records previously excluded. This change will result in an increase of 65,000 carcass weight and rib eye records. The inclusion of these records will cause the EPDs for relatives of animals whose records are now included in the evaluation to change. The IGS genetic evaluation team is in the process of testing the inclusion of these records but at the time of writing this article, the implementation date is unknown.