Expected Progeny Differences

J. M. Rumph, Montana State University
Courtesy of the National Beef Cattle Evaluation Consortium

Expected Progeny Differences (EPD) provide producers with a group of selection tools that specifically address the genetics of the animal. To date, EPD are the best way for producers to predict the relative performance of future progeny for a set of traits. EPD can be a powerful tool for the producer, and with a little knowledge of what each EPD means, they are relatively simple to use.

Statistics Associated with EPD Calculation of EPD requires a great deal of mathematical equations and computing power. As a by-product of these calculations, many other statistics are computed that are of use to the producer. These are typically shown in the first few pages of sire summaries, prior to the EPD tables. This additional information may at first appear Confusing, but with a little explanation, the added information can be of great benefit to the producer.

Breed Averages Breed average EPD provide a benchmark to compare animals to. Just as the name implies, they are the average EPD for animals included in that run of the genetic evaluation. Many associations will also split the breed averages into those for active proven sires, young sires, dams, non-parents, etc. Traditionally, breeds had a base year, and the average EPD in the base year was set to zero, so that any difference from zero would correspond to a difference from the average in the base year, not the current year. Recently, however, some breeds have varied from the base year idea, so it is not as easy to determine what an EPD of zero equates to. What is common across all breeds, however, is that zero does not automatically mean breed average. Growth Traits The earliest developed EPD for beef cattle were for birth weight, weaning weight, yearling weight, and milk. These are still the standard EPD that are calculated for all breeds that conduct genetic evaluations. Even those breeds that have genetic evaluations and that report no other EPD still report birth weight, weaning weight, yearling weight, and milk. 

GROWTH TRAITS

Birth Weight: The birth weight EPD indicates the weight of a bull’s calf at birth and is used as an indicator of the probability of dystocia when that calf is born. Because birth weight EPD is expressed in pounds of birth weight, higher birth weight EPD values indicate larger calves that could result in more calving difficulty. It is normally recommended to use low birth weight EPD sires, especially when breeding heifers.  

Weaning Weight: The weaning weight EPD is measured in pounds of weaning weight and predicts the weight of a bull’s calf at weaning. Because producers selling calves at weaning are usually paid solely by pounds of calf, a higher value is more desirable.This EPD may be of little value for producers retaining ownership of calves beyond weaning, except for its correlated response to general growth, i.e., yearling weight and mature weight. For producers selling calves at weaning by the pound, this is one of the most important EPD to consider when making selection decisions.

Milk: The milk EPD is actually a by-product of the weaning weight EPD. The milk EPD is the maternal portion of weaning weight that is thought to be mainly due to the milk production of the dam. Because of this, the milk EPD is measured in pounds of weaning weight of a bull’s grandprogeny due to the milk production of the bull’s daughters. In areas where feed resources are abundant, selection for increased milk EPD should not be a problem, but in areas where resources are limited and females are retained, care should be taken not to use bulls with high milk EPD. This is because a high milking female will require more feed energy for lactation and have less energy available to put on the condition necessary to rebreed.  This EPD is of no use in terminal mating systems in which heifer replacements are not retained because this predicts the weaning weight of the grandprogeny.  Depending on the breed association reporting the values, sometimes the milk EPD is referred to as the maternal milk, milking ability, maternal, or maternal traits EPD.

Yearling Weight: The yearling weight EPD is measured in pounds of yearling weight and predicts the weight of a bull’s progeny at one year of age. Typically, a larger value is better. This EPD is of use if calves are going to be retained beyond weaning. For production scenarios where calves are sold at weaning or at some point before yearling, this EPD has little value as a prediction of yearling weight; however, its correlation with weaning weight and mature weight (if heifers are retained) can make it valuable. More recently, other growth-related EPD have been developed by some breed associations. These are not reported by all associations.  

Total Maternal: Like milk, total maternal EPD are expressed in terms of weaning weight of a bull’s daughter’s calves. The EPD is calculated by taking half of the weaning weight EPD and adding the  entire milk EPD. This accounts for the half of the weaning weight genetics that the grandprogeny will receive from its dam (the other half will come from the calf ’s sire) and all of the milk production of that calf’s dam. Because this is an indicator of weaning weight (of grandprogeny), a higher value is better, similar to the weaning weight EPD. Because this EPD is used to predict the performance of the bull’s grandprogeny, this EPD is of no use if heifer calves are not being retained as replacements. Depending on the breed association, this EPD is also referred to as the maternal weaning weight, maternal milk and growth, or milk and growth EPD. 

Yearling Height: Yearling height EPD were developed as a frame size selection tool. This EPD is reported in inches of hip height at one year of age. Although intermediate values are usually more desirable, this EPD could also be used to increase the     size so that a herd with mainly small-framed cattle can become more moderate. This EPD is useful for both terminal production systems and those systems where heifers are kept as replacements. Taller calves can be expected to take a longer amount of time on feed in order to reach the Choice grade. For replacements, yearling height is highly correlated with mature height, and this EPD could be used as an indicator for mature size.              

Mature Height: Similar to yearling height, the mature height EPD was also developed as a frame size selection tool. In theory, selection for shorter cows will result in cows that require less feed inputs for maintenance. Therefore, this EPD, which is reported in terms of inches of hip height at maturity, could be used as an indicator of the amount of energy required to maintain heifer      calves once they reach maturity. As a prediction of mature height, this EPD is of no use in a terminal situation where replacements are not retained. It is, however, useful as an indicator of yearling height due to the high genetic correlation between the two traits. Depending on the breed, this EPD is sometimes referred to as the daughter height EPD.

Mature Weight: The mature weight EPD is another indicator for maintenance energy requirements. In theory, when a cow weighs more, she should be expected to require more feed energy in order to maintain herself. Mature weight is reported in terms of the pounds of mature weight of a bull’s daughters and is usually selected for reduced size. If replacement females are not retained, this EPD is not necessary in a selection program. Depending on the breed, this EPD is sometimes referred to as the daughter weight EPD. Reproductive Traits In addition to growth traits, breed associations have also placed an emphasis on developing EPD for reproductive traits. These traits vary from association to association and are listed below.           
Scrotal Circumference: Scrotal circumference is another    indicator trait. The EPD for this trait is used as an indicator for the age at puberty, and consequently, heifer pregnancy of a bull’s granddaughters. In theory, the larger a bull’s scrotal circumference the earlier his daughters will reach puberty. Therefore, the EPD can be used to select for the scrotal circumference of a bull’s sons with implications on the daughters of those sons. The scrotal circumference EPD is expressed in centimeters with a larger number being more desirable. This EPD is of use only in situations in which heifers are retained as replacements.

Gestation Length: Similar to birth weight, the gestation length EPD is another indicator of the probability of dystocia.This EPD is reported in terms of days in utero of a bull’s calves. The longer a calf is in utero, the more that calf will weigh at birth and the higher probability of dystocia. This EPD is also used to provide cows with a longer postpartum interval before having to be rebred for the next year’s calf. Therefore, the gestation length EPD with smaller values are more desirable.
Calving Ease Direct: The calving ease EPD, both direct and maternal, are the economically relevant traits (ERT) that indicator traits, such as birth weight and gestation length, are attempting to predict. calving ease direct EPD are a measure of the ease at which a bull’s calves will be born. This has to do mainly with size and shape of his calves. Calving ease direct EPD are calculated          using information from calvings of two‑year-old females only (no older calvings are included) and the birth weight information of the bull’s progeny (Speidel et al., 2003). In most cases, this EPD is reported as a percentage so that a higher value indicates a higher probability of unassisted calving but is sometimes also reported in ratio form (i.e., 104 versus 4%).

Calving Ease Maternal: Similar to the calving ease direct   EPD, the calving ease maternal EPD is also an ERT for unassisted calving. Contrary to calving ease direct EPD, however, the calving ease maternal EPD predicts the probability of a bull’s daughters calving without assistance. This EPD is also expressed in terms of percentages with a higher value indicating that the bull’s daughters     are more likely to deliver a calf unassisted. Like other EPD that are related to a bull’s grandprogeny, this EPD is of no use unless heifers are retained as replacements. Depending on the breed association, this EPD is sometimes referred to as the calving ease daughters EPD.           

Heifer Pregnancy: Heifer pregnancy is an ERT that indicator traits, such as scrotal circumference, predict. Heifer pregnancy EPD report the probability that a bull’s daughters will conceive to calve at two years of age. This EPD is also reported in percentages where a higher value indicates progeny with a higher probability of conceiving to calve at two years of age. Carcass Traits Carcass traits are another group of traits that have begun to be included in genetic evaluations. These EPD are calculated on an age endpoint as if all cattle were slaughtered at a specific age. Some breed associations report carcass EPD only, some report ultrasound EPD only, and some report both. Even if an association reports only one type of EPD (i.e., carcass), both ultrasound and carcass information may go into the calculation of those EPD because of the genetic correlation between the traits.

For producers who are selling calves based strictly on weight with no premiums for carcass traits and not selling seedstock to customers concerned with carcass traits, both carcass and ultrasound EPD are of limited benefit in selection schemes. 
Carcass EPD: Carcass EPD predict the genetic differences of animals on the rail.

Carcass Weight: Carcass weight EPD report the expected carcass weight, in pounds, of a bull’s progeny when it is slaughtered at a constant age so that producers can select cattle that will produce calves within a certain weight range in order to avoid discounts. There is no ultrasound equivalent to this EPD.

Ribeye Area: Ribeye area EPD are reported in square inches and indicate the area of the longissimus muscle between the 12th and 13th ribs (Boggs et al., 1998) of a bull’s offspring when slaughtered at a constant age. Although bigger is usually better, some grids may discount for ribeyes that are too large. The ultrasound equivalent to this EPD is the ultrasound ribeye area EPD.           

Fat Thickness: This EPD is measured in inches as the prediction of the 12th rib fat thickness of a bull’s progeny when slaughtered at a constant age. A lower value is better to an extent. However, for breeds that are naturally lean, selecting against fat may result in progeny that are too lean, and consequently carcass quality is reduced. Depending on the breed association reporting the estimates, the fat thickness EPD is also sometimes referred to as the backfat             EPD or just simply the fat EPD.

Marbling: The marbling EPD indicates the marbling of the ribeye of a bull’s progeny when slaughtered at a constant age. For most breeds, marbling EPD values range from ‑0.50 to +0.50, which directly corresponds to the scale in Table 6. This means that the difference in marbling expected between the progeny of a bull with a +0.50 and a bull with a ‑0.50 would be a full grade (i.e., Low Choice to Average Choice     or Select to Low Choice). The ultrasound equivalent to this EPD is the percent intramuscular fat EPD. 

Retail Product: This EPD is a prediction of the salable meat that the carcass of the progeny of an animal will yield. It is roughly equivalent to the yield grade EPD because it takes into consideration the same component traits: fat thickness, hot carcass weight, ribeye area, and percentage kidney, pelvic, and heart fat but weighs each component slightly different than for yield grade. The retail product EPD is expressed in percentage units with a higher value indicating that a greater proportion of the carcass is in the form of salable meat. The ultrasound equivalent to this EPD is the ultrasound retail product EPD. Depending on the breed association, this EPD is also called retail yield percent, percent retail, percent retail product, percent retail cuts, or retail beef yield percentage.

 Yield Grade: Similar to the retail product EPD, the yield grade EPD are a measure of lean meat yield of the carcass. All of the same component traits are included in yield grade as in retail product, but each is weighted differently than for retail product. Although retail product is expressed in percent, yield grade is expressed in grade units. The lower the grade, the leaner the carcass, in contrast to retail product where higher values indicate a higher percentage of retail cuts. An animal receiving a calculated yield grade of 1.0 – 1.9 is a Yield Grade 1, an animal receiving a calculated yield grade of 2.0 – 2.9 is a Yield Grade 2, etc. The highest yield grade is 5, so any animal receiving a calculated yield grade of 5.0 or more is classified as a Yield Grade 5. There is currently no ultrasound equivalent to the yield grade EPD.      

Tenderness: The tenderness EPD is measured in pounds of Warner Bratzler Shear Force so that a higher value indicates that more pounds of shear force are required to cut through the meat. Therefore, a lower value indicates more tender meat and is more desirable. There is no ultrasound equivalent to the tenderness EPD.             

Ultrasound EPD: Ultrasound EPD predict differences at ultrasound, which is an indicator of the carcass traits when it is on the rail.    

Percent Intramuscular Fat: The ultrasound equivalent of   the marbling EPD is the percent intramuscular fat EPD. Like the carcass marbling EPD, a higher value indicates more marbling and is generally more desirable.     
For more information click on the following websites:

NATIONAL BEEF CATTLE EVALUATION CONSORTIUM

AMERICAN ANGUS ASSOCIATION