by Dr . Tonya Amen Geneticist for North American Limousin Foundation

recently . These movements were caused by updates that were made to breed effects used in the carcass evaluation . As part of the normal maintenance , it is important to update these effects from time to time as breeds change due to selection .

Due to lack of actual carcass data being submitted , the IGS genetic evaluation uses US-MARC breed effects instead of effects from data in the evaluation . This is common with traits that have limited records , as it is impossible to find enough contemporary groups with breed comparisons to make evaluation of breed effects possible from data submitted by members . In situations like this , it is best to use estimates from scientific literature . These literature estimates are typically from studies that had breeding systems specifically designed for the purpose of obtaining breed effects and are much more reliable than what could be obtained from field data .

The result of the breed effect update is illustrated in the percentile rank tables below — each of these tables is for active sires . In general , we see increases in carcass weight , marbling and fat for both Limousin and Lim-Flex , and a slight decrease in REA .

These shifts will be reflected in comparing bulls with the same breed percentage — the EPDs for bulls of the same breed or breed

continued on page 74

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72 • JANUARY 2021