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Expect Progeny Differences

Since greater than 85 percent of the genetic improvement in a cow herd comes from the sire, effective and appropriate sire selection decisions are imperative to the sustained profitability of a cow calf enterprise. Although many selection tools exist, expected progeny differences, or EPDs, are the most accurate, effective and widely used selection tool available, so it is important to understand their meaning and interpretation.

EPDs are predictions of relative genetic merit expressed as the expected difference in performance between one animal’s progeny when compared to another, and are based upon individual, progeny and ancestral performance, ancestral relationships, and genomic data. Although often perceived as absolutes, EPDs can and will vary.

When an animal is young and only limited information is available, EPDs assume the individual received a random assortment of genes from the parents. However, as breeders report progeny performance data on the animal and its progeny, EPDs change. The extent to which EPDs can vary is dependent upon their associated accuracy, which is a measure of the reliability of the EPD, and in effect, represents the probability that the estimate is correct. Within a given level of accuracy, there is a range within which the EPD will most likely stay, which is termed the possible change value. Possible change values are the standard deviation for the EPD at a given accuracy, meaning that around two-thirds of the time, the EPD will fall within the possible change values.

Consider comparing two yearling bulls using birth weight EPD. Sire A has a birth weight EPD of 0.0, and sire B has a birth weight EPD of +5.0. Because neither bull has any progeny records, each bull’s individual performance and ancestral records contribute to the EPD, and accuracy will be relatively low (approximately 0.35). The accuracy value indicates that the current estimate or EPD has a 35 percent chance of being the true relative progeny performance value of these two bulls. The possible change value of birth weight EPD at this accuracy is approximately 1.7, meaning that sire A’s true progeny performance value for birth weight would likely fall within ± 1.7 lbs. of 0.0 (-1.7 to +1.7) and sire B’s true progeny performance value would likely fall within ± 1.7 lbs. of 5.0 (+3.3 to +6.7) two-thirds of the time.

Since greater than 85 percent of the genetic improvement in a cow herd comes from the sire, effective and appropriate sire selection decisions are imperative to the sustained profitability of a cow calf enterprise. Although many selection tools exist, expected progeny differences, or EPDs, are the most accurate, effective and widely used selection tool available, so it is important to understand their meaning and interpretation.

EPDs are predictions of relative genetic merit expressed as the expected difference in performance between one animal’s progeny when compared to another, and are based upon individual, progeny and ancestral performance, ancestral relationships, and genomic data. Although often perceived as absolutes, EPDs can and will vary.

When an animal is young and only limited information is available, EPDs assume the individual received a random assortment of genes from the parents. However, as breeders report progeny performance data on the animal and its progeny, EPDs change. The extent to which EPDs can vary is dependent upon their associated accuracy, which is a measure of the reliability of the EPD, and in effect, represents the probability that the estimate is correct. Within a given level of accuracy, there is a range within which the EPD will most likely stay, which is termed the possible change value. Possible change values are the standard deviation for the EPD at a given accuracy, meaning that around two-thirds of the time, the EPD will fall within the possible change values.

Consider comparing two yearling bulls using birth weight EPD. Sire A has a birth weight EPD of 0.0, and sire B has a birth weight EPD of +5.0. Because neither bull has any progeny records, each bull’s individual performance and ancestral records contribute to the EPD, and accuracy will be relatively low (approximately 0.35). The accuracy value indicates that the current estimate or EPD has a 35 percent chance of being the true relative progeny performance value of these two bulls. The possible change value of birth weight EPD at this accuracy is approximately 1.7, meaning that sire A’s true progeny performance value for birth weight would likely fall within ± 1.7 lbs. of 0.0 (-1.7 to +1.7) and sire B’s true progeny performance value would likely fall within ± 1.7 lbs. of 5.0 (+3.3 to +6.7) two-thirds of the time.


Author: Kevin Shaffer, WVU Extension Service Livestock Specialist
Last Reviewed: February 2018
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