EPDs and $ Indexes
[Originally printed in the Indiana Beef Evaluation Program (IBEP) sale catalog]
Donna L. Lofgren
Department of Animal Sciences, Purdue University
Development of animal breeding models and advances in computer technology have provided beef producers with selection tools which allow animals within a breed to be compared for their genetic merit. These selection tools are Expected Progeny Difference (EPD) for individual traits, and $ Indexes which combine several EPDs into one economic value. Individual beef breed associations conduct National Cattle Evaluations (NCE) once or twice each year. The NCE combine individual records with pedigree and progeny data to calculate EPDs. Interim EPDs are calculated for young animals whose records are processed between the times of the NCE.
The difference in EPD of two bulls is the difference in expected progeny performance of their progeny, if the bulls are mated to similar cows and their progeny are in similar management and environmental conditions. EPDs are expressed in the same units as the trait. For example, Birth Weight, Weaning Weight, and Yearling Weight EPDs are in pounds, while Carcass Fat EPD is in inches. The sign of the EPD indicates direction; positive means larger (heavier weights), and negative (-) means smaller (lighter weights). Which direction is “good” depends on the trait. Positive EPDs would be good for weaning weight but may be bad for birth weight. EPDs are valid only for comparing bulls of the same breed. Do not compare EPDs of bulls in different breeds.
Growth and Maternal Traits
- Birth Weight, in pounds, predicts the weight at birth of the bull’s progeny compared to progeny of other bulls. A bull with an EPD of -1 is expected to have progeny which average 3 lb lighter than progeny of a bull with an EPD of +2.
- Weaning Weight, in pounds, is a measure of the weaning growth of the bull’s progeny. Higher EPDs mean heavier calf weights. • Yearling Weight, in pounds. Higher EPDs mean heavier weights for the bull’s progeny.
- Maternal Milk, in pounds, is measured by the weaning weight of the calves. It predicts the milking ability of the bull’s daughters, expressed as her calf’s weaning weight. Higher EPDs mean heavier calf weights due to the daughter’s milking ability.
- Direct Calving Ease is a measure of the ease with which a bull’s calves are born to first calf heifers. Higher EPDs mean fewer assisted births.
- Maternal or Daughters’ Calving Ease is a measure of the ease with which a bull’s daughters calve as first-calf heifers. Higher EPDs mean fewer assisted births.
Carcass and Ultrasound Traits
Carcass traits may be measured at slaughter, or measured on live animals using ultrasound. Many breeds report EPDs for carcass or ultrasound traits, using one type of measurement or a combination of both. All measure the expected performance of the bull’s progeny. Different breeds calculate EPDs for different traits. For Angus, EPDs are calculated for both carcass and ultrasound traits. Some breeds update interim EPDs after the bulls are scanned during the test.
- Carcass Weight (carcass trait), in pounds. Higher EPDs mean heavier weights.
- % Intramuscular Fat (ultrasound trait) is a measure of the percent intramuscular fat (marbling) in the ribeye of the bull’s progeny. Higher EPDs mean a higher % intramuscular fat.
- Marbling (carcass trait) is a measure of the marbling score of a bull’s progeny. It is a subjective measure of % intramuscular fat. Higher EPDs mean higher marbling scores.
- Fat Thickness (carcass and ultrasound trait), in inches, measures the fat thickness at the 12th rib of the bull’s progeny. Higher EPDs mean greater fat thickness.
- Ribeye Area (carcass and ultrasound trait), in square inches. Higher EPDs mean a larger ribeye area.
- Yield Grade (carcass) is a measure of the relative proportion of closely trimmed, boneless retail cuts from the bull’s progeny. Higher EPDs mean higher yield grades, and thus a lower proportion of retail cuts.
These are multi-trait selection indexes, which combine EPDs for several traits into a single economic value, which can be used to make selection decisions. The index values are interpreted like EPDs; the difference in index value between two bulls is the expected difference in average dollar value of their progeny, when the bulls are bred to similar cows. Typical beef production and economic values are used in calculating the indexes. Indexes are expressed in dollars per head, and higher indexes mean a higher dollar value per head. An index value only has meaning when it is compared to the index value of another animal of the same breed. Currently, indexes are calculated for Angus, Gelbvieh, Hereford, Simmental, and SimAngus bulls.
- Angus $W is Weaned Calf Value. This is the expected average of future progeny for preweaning performance, within a typical beef cowherd. It accounts for the economic impact of birth weight, weaning weight, maternal milk, and mature cow size.
- Angus $F is Feedlot Value. This is the expected average of future progeny for postweaning feedlot performance.
- Angus $G is Grid Value. This is the expected average of future progeny for carcass grid merit. • Angus $B is Beef Value. This is the expected average of future progeny for postweaning performance and carcass value. The $B value combines information from $F and $G.
- Gelbvieh FM is Feedlot Merit. This is the expected average of future progeny for postweaning feedlot performance.
- Gelbvieh GM is Grid Merit. This is the expected average of future progeny for carcass grid merit.
- Hereford BMI$ is Baldy Maternal Index. This is the expected average performance of progeny of Hereford bulls used in rotational crossbreeding programs on Angus-based cows and heifers, with the progeny marketed on a Certified Hereford Beef LLC pricing grid.
- Hereford BII$ is Brahman Influence Index. This is similar to BMI$, except that the bulls are mated to Brahman-based cows. It puts more emphasis on fertility and age at puberty, and less on growth and calving ease.
- Hereford CEZ$ is Calving Ease Index. This is similar to BMI$, except that the bulls are mated only to yearling heifers. It has increased emphasis on calving ease.
- Hereford CHB$ is Certified Hereford Beef Index. This is the expected average performance of progeny of Hereford bulls mated to British-cross cows, with all progeny sold as fed cattle on a Certified Hereford Beef LLC pricing grid. It is a terminal sire index, including growth and carcass information only, since all progeny are marketed and no females are retained in the herd.
- Simmental and SimAngus TI is Terminal Index. This is the expected average performance of progeny of Simmental bulls mated to mature Angus cows, with all offspring placed in the feedlot and sold grade and yield. It includes growth and carcass information only, since all progeny are marketed.
- Simmental and SimAngus API is All-Purpose Index. This is the expected average performance of progeny of Simmental bulls used on the entire Angus cowherd, with a portion of the daughters being retained for breeding and the remaining progeny being put on feed and sold grade and yield.
Most EPDs are reported with an Accuracy (ACC) value, which ranges from 0 to 1. It is a measure of the reliability of the EPD. EPDs will change and become more accurate as additional data on the bull and his relatives are processed by the breed association. For most yearling bulls, ACC is low, because they have not sired any progeny. Some breeds report the accuracy of these EPDs as BK, I, P, P+, or PE. These indicate that the EPD is based on pedigree data, or is an interim EPD based on pedigree data and the bull’s own performance.
Average EPDs for most traits are not zero. The actual average will be different for each breed. Percentile tables must be used to determine where a bull's EPDs and indexes rank within the breed. EPDs and $ Indexes for the bulls in the IBEP test should be compared to percentiles for non-parent bulls of the same breed. Look up the bull's EPD in the table to determine where he ranks in his breed. Remember that for most traits, a positive EPD is desirable. However, for Birth Weight, Carcass Fat, Ultrasound Fat, and Yield Grade, a negative EPD is desirable. Percentile tables are available from the breed associations.
References and Contact Information
This article originally appeared in the Indiana Beef Evaluation Program (IBEP) sale catalog.
For more information or questions, please contact Donna L. Lofgren, Department of Animal Sciences, Purdue University at firstname.lastname@example.org.