The Value of Accuracy
Keep accuracy in mind when making decisions, but don’t select solely on it.
DES MOINES, IOWA (June 23, 2021) — Accuracy, ironically, is a concept that is often misunderstood. This is at least true in the sense of expected progeny differences (EPD), says Matt Spangler, professor and beef genetics specialist at the University of Nebraska–Lincoln. Too often, he told attendees of the 2021 Beef Improvement Federation (BIF) Advancements in Producer Applications breakout session, cattle producers select for accuracy instead of the EPD itself. This limits the amount of change you’re trying to make.
Should accuracy be considered? Absolutely, said Spangler. Should it be the main criteria? No.
“The value of accuracy for commercial producers is personalized,” Spangler said. “It depends upon your risk tolerance.”
Consideration of accuracy for a trait is also dependent on your herd’s current performance and breeding objectives, he explained. If you currently have no issues with calving ease, then you don’t need to worry as much about the accuracy of a bull’s calving ease EPDs. If you are trying to make significant change in marbling, for instance, then accuracy has greater weight.
Accuracy provides an indication of how likely a sire’s EPDs will hold true in predicting the average performance of his offspring, but not the difference between every calf born. It does not tell us the consistency of offspring, Spangler admitted. Thanks to Mendelian sampling — the random passing of alleles — calves will have varying degrees of a sire’s genetic traits. Accuracy can’t change that.
Accuracy tells us how much the EPD could change with more information. More progeny give us more data. So, if a bull already has many progeny, his accuracy is higher because his EPD is less likely to change.
While accuracy is more complex than meets the eye, possible change is much more palatable, Spangler said. Most breed associations publish these possible change values. These are the equivalent to the standard error of prediction (SEP), or a standard deviation. It reflects how much an EPD can change going from current information to complete information on an animal, he explained.
Spangler noted that 68% of the time, an EPD will not move outside one SEP in either direction. And 95% of the time, the EPD will fall withintwo SEPs in either direction. Spangler recommended determining your threshold EPD within the range of 68% or 95% confidence. If you’re not willing to go below a certain EPD number for a specific trait, then you may want to add twice the possible change number into your threshold so your desired genetic change will stay within your herd’s breeding objectives.
Progeny data increases accuracy the most, regardless of heritability of the trait, Spangler noted. Genomic data also increases accuracy, but only because it speeds up progeny information. Phenotype records are still necessary to increase accuracy.
One underused practical note is increasing accuracy through a mean, Spangler said.
“As I increase the number of individuals in a group, I have more confidence in the mean — the average — of the individuals. If I turn out a large group of bulls in a pasture, it’s not the individual genetic merit that I’m really interested in, it’s the average of their genetic merit,” Spangler said. “The accuracy of that average will always be exceptionally high.
“If you use one bull, there is a greater chance that he changes. If you use five or 10 bulls with similar genetic value, you spread the risk out,” he clarified.
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