EPD and Index Definitions

The most effective tool available for comparing the genetic merit of a single trait between individuals is expected progeny differences (EPD). These values are estimates of the genetic potential that parents will pass on to progeny. An animal’s EPD estimates the additive or direct genes that can be inherited for specific traits (weight, gain, marbling, etc.).

An EPD uses all available information tied to the genetics of a trait including an animal’s own performance data, performance data on relatives, genomics, and progeny data. It’s important to remember that EPD continue to get more accurate and are subject to change as more information is reported. 

In using EPD, the difference between two sires’ EPD represent the unit difference expected in the average performance of their progeny. For example, if sires A and B have EPD of +20 and +10, a 10-unit difference would be expected in the average of their progeny. The key to using EPD is knowing what units they are expressed in. For example, if the above case referred to weaning weight EPD, sire A’s progeny would be expected to weigh on average 10 pounds heavier at weaning compared to sire B’s progeny. If the trait was calving ease, sire A would be expected to sire 10 percent more unassisted births in first-calf heifers on average compared to sire B. 

Percentile ranking is helpful to determine where any EPD ranks relative to the rest of the breed.

CALVING EASE DIRECT (CE)

• Reported as the difference in probability of calves being born unassisted out of first-calf heifers.

• Higher values are more favorable.

CALVING EASE MATERNAL (MCE)

• Reported as the difference in probability of daughters calving unassisted as first-calf heifers. 

• Higher values are more favorable.

MILK (MLK)

• Reported as the difference in maternal pounds of weaning weight from an individual’s daughters due to milk.

• Desirable values are dependent on management constraints.

MATERNAL WEANING WEIGHT (MWW)

• Reported as the pounds of weaning weight expressed in daughters’ progeny due to the milk production of the daughter and the direct genetic effect for weaning growth. 

• Higher values are more favorable.

STAYABILITY (STAY)

• Reported as the difference in probability of a sire’s daughters staying in the herd until 6 years of age, given that they calved as a 2-year-old. 

• Higher values are more favorable.

Mature Weight (MW)

• Reported as the difference in pounds of cow body weight at six years of age and body condition score of 5.
• A higher value indicates a genetic tendency for heavier daughters at maturity. A lower value indicates a genetic tendency for lighter daughters at maturity.

Cow Energy Requirement (CER)

• Reported as the yearly difference in pounds of total digestible nutrients (TDN) required for a cow aged six years.
• A lower value indicates a genetic tendency for daughters that require less energy to support production. A higher value indicates a genetic tendency for daughters that have higher energy demands.

DOCILITY (DOC)

• Reported as the difference in yearling-age progeny temperament, represented as a difference in probability that progeny will be scored as a 1, rather than a 2-6 on the docility scale.

• The docility scale subjectively orders individuals on temperament from docile disposition (1) to extremely aggressive (6). 

• Higher values are more favorable.

BIRTH WEIGHT (BW)

• Reported as the difference in pounds of calf birth weight.

• Desirable values are dependent upon management goals, however if selecting for reduced calving difficulty the appropriate EPD to use is CE.

WEANING WEIGHT (WW)

• Reported as the difference in pounds of progeny weaning weight.

• Higher values are more favorable.

YEARLING WEIGHT (YW)

• Reported as the difference in pounds of progeny yearling weight.

• Higher values are more favorable.

AVERAGE DAILY GAIN (ADG)

• Reported as the difference in post-weaning pounds gained on a daily basis.

• Higher values are more favorable.\

DRY MATTER INTAKE (DMI)

Reported as the difference in pounds of daily dry matter intake.

Lower values indicate the genetic potential for progeny to consume less feed.

CARCASS WEIGHT (CW)

• Reported as the difference in pounds of progeny carcass weight.

• Higher values are more favorable. Only economically relevant if producers retain ownership or are driven by terminal performance.

RIBEYE AREA (REA)

• Reported as the difference in square inches of ribeye area between the 12th and 13th rib.

• Higher values are more favorable. Only economically relevant if producers retain ownership or are driven by terminal performance.

BACK FAT (BF)

• Reported as the difference in inches of external backfat at the 12th and 13th rib.

• Lower and more negative values represent less backfat, resulting in leaner carcasses, and are more favorable. Only economically relevant if producers retain ownership or are driven by terminal performance.

YIELD GRADE (YG)

• Reported as the difference in progeny USDA Yield Grade score units (1–5).

• Lower values represent leaner carcasses with more saleable beef. Only economically relevant if producers retain ownership or are driven by terminal performance.

MARBLING SCORE (MARB)

• Reported as the difference in progeny carcass marbling score. 

• Higher values are more favorable.

• A genomic panel is not guaranteed to move EPD in a favorable direction. In fact, all animals have equal opportunity to have EPD move in a favorable or unfavorable direction after a test. 
• The real value in performing a genomic panel on groups of young animals is by increasing accuracy of the prediction. This allows potential purchasers to have more confidence in the predictions, as well as increasing the rate of genetic progress in their herds. 
• You must allow at least one and up to two weeks from the date a genomic sample finishes at the lab for those results to be incorporated into the genetic evaluation. 
• Phenotypes are still needed to continue to predict traits with accuracy. A genomic test will improve the accuracy of low- to medium-accuracy animals, but genomics alone can never replace the need for phenotypic measurements.