The beef cattle industry has been using Expected Progeny Differences (EPDs) as a selection tool in improving calf productivity for nearly two decades. An EPD is the difference in performance (measured in pounds, percent, inches, etc.) expected in progeny, or offspring, of individual sires.
Sire summaries are produced and published by breed associations to provide up-to-date genetic evaluations on progeny of proven sires within their breeds. While sire-summary formats may vary between breeds, they're designed to use unbiased prediction procedures for all cattle in their breed that have legitimate performance records or progeny with legitimate performance records.
EPDs provide a genetic description of an animal for the traits included in the analysis, and is the best estimate of an animal's genetic worth given the data for analysis. They are expressions of the relative genetic merit of beef cattle for various traits. EPDs are used to compare the predicted progeny performance between two animals (bulls or females) within a breed, regardless of herd location or age.
Normally, the EPDs of bulls from different breeds can't be compared because most breed associations compute their EPDs in separate analyses, and each breed has a different base point where the average EPD = 0 (see “Across-breed EPDs”).
Actual units of measure
EPDs are expressed in the actual units of measure for a given trait. EPDs for traits such as birth weight (BW), weaning weight (WW) and yearling weight (YW) are expressed in pounds. Since EPDs are used to compare two bulls (or females) within a breed, the difference in the EPDs for those animals compared would be the predicted differences in the average performance of those two animals' progeny. For example, consider the EPDs for bulls in Table 1.
These EPDs do not mean that bull A would increase a herd's birthweights by 5 lbs. and add 22 lbs. to the calves at weaning, and 40 lbs. to the calves as yearlings. They simply allow us to predict the difference between the average weights of the two bulls' calves if they were mated to the same group of cows.
When compared to bull B, we can expect calves from bull A to average 6 lbs. more at birth, 15 lbs. heavier at weaning, and 10 lbs. heavier as yearlings.
In addition to the numerical EPD (can be positive or negative), an accuracy value (ACC - 0.00 to 1.00) for that EPD will also be calculated during the breed's genetic evaluation analysis. This is a measure of confidence that the EPD reflects the true genetic merit of an animal.
As the amount of information that goes into the calculation of an EPD increases, the accuracy of that EPD increases. EPDs with low levels of accuracy (.07 to .30) are likely calculated with no progeny information included. Thus, they are more susceptible to change during the next evaluation when more data are included in the analysis.
EPDs with high levels of accuracy (.80 to .99) already have included a large number of progeny and are less subject to dramatic changes.
Across-breed EPDs (AB-EPDs) have been developed to help manage genetic uniformity when multiple breeds are rotated in a crossbreeding system.
By using the across-breed adjustment factors, animals of different breeds can be compared on the same EPD scale.
The AB-EPDs are most useful to commercial producers purchasing bulls of more than one breed to use in crossbreeding programs. Uniformity from one generation to the next can be improved by selecting bulls with similar AB-EPDs.
Selection for uniformity is especially important for traits such as birth weight to manage calving difficulty, and for traits related to cow size and milk production to effectively manage feed requirements in cow herds.
In terminal cross-breeding systems, AB-EPDs for growth traits can be used to identify bulls across breeds whose progeny should have the highest growth potential. AB-EPD adjustment factors are updated each year using EPDs from the most recent national cattle evaluations conducted by each of the 16 breed associations.
The breed differences used to calculate the factors are based on comparisons of progeny of sires from each of these breeds at the U.S. Meat Animal Research Center in Clay Center, NE.
For more on AB-EPDs, go to: www.beefimprovement.org/2007_ABEPD_press_release.pdf
Clint Peck is director, Beef Quality Assurance, Montana State University.
Editor's Note: The “Cow Marketing” section in last month's BEEF Basics column should have been attributed to Jason K. Ahola, University of Idaho Extension beef specialist. We apologize for the omission. Contact him at email@example.com or 208-454-7654.
|Source: University of Tennessee|
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