The amount of data available from Estimated Progeny Differences (EPDs) continues to increase – but you can make interpreting it as simple, or as complex, as you want.
Cattle EPDs compare traits such as calving ease, average daily gain, and carcass characteristics with others in the breed; the more information that’s available on an animal, the more accurate the EPD. Tonya Amen, genetic service director for the St. Joseph, Mo., based American Angus Association (AAA), told Ozarks Farm & Neighbor it starts with pedigree information. “We will likely, for registered animals, have an EPD on their sire and dam, and we will make use of that information to calculate an interim EPD on young animals,” she said. “From there, as our breeders start collecting performance information for their animals – for instance taking birth weights on calves, weaning weights or yearling weights – an animal’s own performance information goes into their EPD, assuming they came from a proper, contemporary group.” Eventually, as the animal is used as a sire or dam, the information from its progeny is also added to its EPD; for AI bulls, with many calves on the ground, the accuracy rates become very high.
AAA is also incorporating information from DNA tests into EPDs; the breed association’s Angus Genetics subsidiary has just completed a recalibration of its HD 50K test. Amen said, “We compare Molecular Breeding Values, the results of the DNA tests that we get from the two companies that we work with – Pfizer and Igenity – to our gigantic database that we have with performance information, and we determine in house at American Angus just how closely those genomics line up with actual performance data.” For instance, she said, if the HD 50K test is run for birth weights on an unproven animal, the addition to the EPD is the equivalent of the animal already having 10 offspring; some other traits yield even more information.
If a producers is selecting replacement heifers, Amen suggested they might gain the most insight from two calving ease EPDs – Direct, which predicts how easily the bull’s own calves will be born to first-calf heifers, and Maternal, which gauges how easily the bull’s daughters would be expected to calve as first calf heifers. Angus is among several breeds that offers a heifer pregnancy EPD, and its residual average daily gain EPD is unique. Amen said, “It’s interpreted in pounds per day, so if we were to compare two bulls for residual average daily gain, let’s say one has an EPD of 0.23 and another bull has zero. We would expect offspring of the bull with the 0.23 to gain almost a quarter of a pound more per day, while eating the same amount.”
In a recent blog entry, University of Arkansas Extension Animal Science professor Shane Gadberry used data and sales prices for the 54 bulls listed in the catalog of the Northeast Arkansas Angus Association’s 2012 fall sale to determine what buyers were looking for in their bull purchase. Gadberry wrote, “The correlation analysis with sale price included age, weight, and catalog EPD data for the bull being sold, and the EPDs of the bull’s sire. In addition, each bull’s sire was categorized into 1 of 4 popularity ranks, based on the amount of records that contributed to maternal and carcass EPDs,” with 4 being “proven” and “well-recognized.”
Among his findings were that buyers paid less for bulls with higher birth weight EPDs, and more for those with higher yearling weight EPDs. “This suggests that buyers were interested in a lot of post-weaning growth potential,” he wrote.
Gadberry found the EPD that exhibited the strongest relationship with sale price was the maternal milk EPD. “This suggests buyers were looking for sires that could increase the weight of calves through the heifers they produced,” he wrote. He concluded that 46-52 percent of the difference in bull prices was due to premiums buyers paid for heavier bulls that would be expected to produce calves with greater growth potential either through milk production of daughters or post-weaning weight gain; the rest of the difference he attributed to such factors as the intended use of the bull, the reputation of the seller, the bull to buyer ratio, and the buyer’s goals.
But Amen said EPDs have definitely contributed to genetic improvement over time. “We can really see evidence of when EPDs were implemented and when breeders really started using them; for instance, marbling has been improving over time, and weaning weights and yearling weights have been improving drastically over time,” she said. “You would think, if we’re having improved weaning and yearling weights, that birth weight as a gross trait would track right along with them. But because our producers have been using EPDs they’ve been able to hold birth weight down and still increase those other two traits as well.”
