EPD Accuracy: What It Is, What It’s Not
Higher accuracy values foster confidence a sire’s calves, on average, will perform as predicted; however, they provide no measure of consistency within a set of calves.
DES MOINES, Iowa (June 23, 2021) — When choosing a breeding bull from among candidates with recorded expected progeny difference (EPD) values, should you select on the basis of the EPDs or make a selection based on the accuracy of the EPDs? University of Nebraska Beef Cattle Geneticist Matt Spangler posed that question to an audience gathered for the 2021 Beef Improvement Federation (BIF) Research Symposium & Convention hosted June 22-25 in Des Moines, Iowa.
“All too often, people select for accuracy first and EPD second,” said Spangler, calling that approach to genetic selection flawed.
Spangler explained that the accuracy assigned to an EPD is a numerical expression of how much information went into its calculation. Increased accuracy, therefore, gives us more confidence in the cumulative genetic merit of an individual as a parent.
While that is advantageous, Spangler advised breeders to recognize what accuracy does not do.
“Something important to know, but often misinterpreted, is that high-accuracy bulls will have offspring that are as variable as low-accuracy bulls,” stated Spangler. “Accuracy does not tell us anything about the consistency of the offspring.”
Discussing factors that increase EPD accuracy, Spangler said increased progeny data is foremost. More progeny providing more data is key. Genomic data also adds accuracy, especially for young animals with few or no progeny, but it does not negate the need for progeny performance records.
Spangler said the value of accuracy to seedstock breeders is more similar than for commercial cow-calf producers. For the latter, the value of accuracy is personalized and dependent on two principal factors. First, it depends on their respective needs — their herd’s current performance and their individual breeding objective. As an example, Spangler explained that selecting sires for calving ease is important to a herd with a history of dystocia, but less important when choosing a bull to mate with cows with no history of calving difficulty.
Secondly, the value of accuracy depends on a commercial producer’s risk tolerance. The risk-averse producer who insists on using only bulls with high-accuracy EPDs is likely to sacrifice some genetic progress and profit potential.
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