Following are short definitions for what each Gelbvieh EPD measures and the unit it is measured in. For updated average EPDs for the Gelbvieh breed, visit www.gelbvieh.org.
Calving Ease Direct (CE): an EPD that is expressed as a ratio, with a higher ratio representing better (easier) calving ease. This value represents the direct influence a sire has on calving ease. Only first-calf heifer data is included.
Birth Weight (BW): predicts the difference, in pounds, for birth weight. Weaning Weight (WW): predicts the difference, in pounds, for weaning weight (adjusted to age of dam and a standard 205 days of age). This is an indicator of growth from birth to weaning.
Yearling Weight (YW): predicts the expected difference, in pounds, for yearling weight (adjusted to standard 365 days of age). This is an indicator of growth from birth to yearling.
Milk (MK): the genetic ability of a sire's daughters to produce milk expressed in pounds of weaning weight.
Total Maternal (TM): a value that combines growth and milk information and a prediction of the weaning weight performance of calves from a sire's daughters. This value does not have an accompanying accuracy value. Gestation Length (GL): this EPD is expressed in days and measures the days under or over normal gestation length a sire's daughters can be expected to calve.
Calving Ease Daughters (CED): an EPD expressed as a ratio for a sire's daughters' calving ease with a higher ratio being a more favorable calving ease. This value represents the calving ease that a sire transmits to his daughters. Only first-calf daughters are considered in calculating the EPDs. Scrotal
Circumference (SC): value is expressed in centimeters of adjusted yearling scrotal circumference.
Stayability (ST): predicts the genetic difference, in terms of percent probability, that a bull's daughters will stay productive within a herd to at least six years of age. Stayability EPD is one of the best measures currently available to compare a bull's ability to produce females with reproductive longevity.
Carcass Weight (CW): expressed in pounds of carcass weight.
Rib Eye Area (RE): expressed in square inches of rib eye muscle area.
Marbling (MB): expressed in degrees of marbling score, a determinant of USDA Quality Grade.
Feedlot Merit (FM): expressed in dollars per head, value passed to progeny. The F eedlot Merit EPD measures the dollar value associated with the expected gain and feedlot efficiency of progeny when fed in a "typical" feedlot arrangement.
Mastering EPD Accuracy
Accuracy (Acc) is an expression of reliability of the EPD. Accuracy may range from 0.0 to 1.0. As accuracy approaches 1.0, the EPD is more reliable and can be expected to change less in the future as more progeny data are accumulated.
Accuracy may be categorized into low, medium and high reliability as follows: Low 0.0 to .59; Medium .60 to. 79; High .80 to 1.0. EPDs should be used to decide which bulls are selected while accuracy values suggest how extensively the bulls should be used. Bulls with favorable EPD values and high accuracy values can be used with confidence that they will contribute favorably to genetic improvement of the herd.
Accuracy is an abbreviated method of expressing the reliability of an EPD. Another more specific indicator is the standard error of prediction (possible change). Changes in EPD can be expected to fall within the possible change range 67 percent of the time.
As accuracy increases, the possible change decreases. For example, if the accuracy of a bull's yearling EPD is .20, the expected possible change in EPD is ±22 lb. (potential range in EPD = +38 to +82 lb. for a bull with a yearling weight EPD of +60 lb.). If the yearling weight EPD accuracy is .80, the possible change in EPD decreases to ±7 Ib. (possible range in EPD = +53 to +67 lb. for a bull with a yearling weight EPD of +60 lb.).
Heritability Estimates and Trait Correlations
Heritability may be defined as the portion of the differences among sire progeny groups that is due to genetic variation. For a trait that is 40 percent heritable, 40 percent of the variation in thecontemporary group is due to genetics and 60 percent is due to environment. The higher the heritability, the easier it is to make a genetic change in one specific trait. Since heritability is already considered in their calculation, EPDs reflect actual genetic differences. The heritability estimates given in Table 1 are those calculated by the University of Georgia for Gelbvieh used in the NCE analysis.
TABLE 1. Heritability Estimates for Gelbvieh
|Calving Ease - Direct
||Daughters Calving Ease
For more information, visit www.gelbvieh.org/pdf/tech/tech_epd_accurac_med[l].pdf.