Selection Indices: Beware Unintended Consequences
Users of selection indices should be cognizant of changes in other correlated traits.
DES MOINES, IOWA (June 24, 2021) — Substituting for her colleague at Neogen Genomics, geneticist Kari White spoke to the Advancements in Selection Decisions breakout session of the 2021 Beef Improvement Federation Research Symposium & Convention hosted June 22-25 in Des Moines, Iowa. White offered an explanation of selection indices and tips regarding the application in genetic selection.
“A selection index really is just a cumulative number used to select for several traits at one time,” stated White, explaining that multiple expected progeny difference (EPD) values, weighted according to their importance to a breeding objective, are combined into a single value. This selection index is then used to rank individual animals according to their usefulness to the breeding objective.
White reminded her audience that no selection is made in a vacuum. Selection for one trait affects every correlated trait, either positively or negatively. According to White, that’s why users of selection indices should care less about the traits included and the coefficients, and care more about the correlation of traits.
White exhibited samples of selection indices developed for American breeds, including Brangus, Santa Gertrudis and Beefmaster. Her samples illustrated correlations among traits whose EPDs were included in index calculations and traits not included.
“When using an index, your selection decisions always affect other traits — even traits not included in the index. We need to be cognizant of that,” White advised. “There are always unintended consequences.”
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