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.