| Everyone has an opinion on the importance of EPDs to their program. While not an exact science the use of EPD data is an important tool that can be used in all areas of your herd management and genetic selection. Hereford BW EPD's are on a fixed scale from 1970 and Red Angus are on a floating scale. We have attempted to reflect the general explanation and source of each EPD category. First printed in the Star Lake 2005 Al Semen Guide, this glossary has generated a huge amount of favorable comments.
CED (Calving Ease-Direct): A positive number or higher number for this EPD indicates easier calving ease. The CED EPD predicts the ease with which the progeny of the individual should be born. This EPD is derived from the calving ease scores turned in, with birth weight for the animals in the pedigree being a major part of this formula. Consider selecting for either CE or BW, not both, because doing both over-emphasizes BW.
BW (Birth Weight): Derived from the actual birth weight ranking within the contemporary group where the calf was born. The first BW EPD issued for a calf is the average of the dam and the sire, with an adjustment made from that number to reflect the actual birth weight of an individual as compared to its contemporary group average. An actual birth weight that is exceptionally higher or lower than the average of its contemporary group will change that individual’s BW EPD accordingly. The BW EPD is primarily changed when progeny have been recorded from the subject animal and the accuracy becomes much higher. The birth weight is adjusted according to the age of dam. The BW EPD has no correlation to an actual birth weight (an 85 lb. calf can have a BW EPD of 4.5 or 5.5 or 6.5 or even a 2.5 in different herds). A lower number is desirable and indicates less expected birth weight.
WW (Weaning Weight): An EPD to measure the growth genetics up to weaning age (205 days). This growth EPD is derived from the weaning weights turned in for contemporary groups. This EPD is generally very indicative of the growth up to weaning age, based on the genetic history of the animals in the pedigree. Actual weaning weights are adjusted for the age of dam. Weaning weights have been taken and recorded more than most any other EPD trait. The accuracy is important to the possible changes of this and all EPDs. The WW EPD has a significant effect on YW EPD, as well.
YW (Yearling Weight): An EPD to measure the growth from weaning age to yearling age. The YW EPD is tied to the WW EPD; the growth of the individual through yearling is effected by weaning weight. This EPD will be fairly indicative of the genetics in the pedigree as we in the industry have taken weaning and yearling weights as actual measurements longer than many traits measured and with fewer adjustments. The accuracy is important to the YW EPD as to the amount of possible fluctuation that may occur.
MM (Maternal Milk): An EPD derived from weaning weight to measure the milking ability of the individual. MM is that part of WW due to a dam’s milking ability. A proven bull’s milk EPD is derived nearly 100% from his daughters in production. When a bull is born, his MM EPD is the average of his sire and dam. The EPD has low accuracy and will change according to how his sire or dam may change. When his daughters go into production, the way they produce in their contemporary groups, either by being above average or below average, will change the sire’s MM EPD accordingly. At this point the accuracy will go up, which gives a truer picture of the bull’s actual ability to genetically pass milk to his progeny. A proven cow’s milk EPD is derived from her own production and her daughters in production. A cow’s own production contributes to less than 50% of her own MM EPD. Her daughters in production contribute over 50% to her own MM EPD. The MM EPD has much more meaning for bulls and cows old enough to have daughters in production.
M&G (Maternal Milk & Growth): This EPD is 1/2 of WW plus MM = M&G. This EPD is sometimes referred to as Total Maternal or Combined Maternal. This is an EPD that reflects the combined WW and MM EPD. It reflects the growth to weaning age plus the milk production to weaning time. It is an estimate of daughters’ progeny weaning weight.
CEM (Maternal Calving Ease): This EPD indicates the ability of a sire’s daughters to have a calf at two years of age. Higher or positive numbers meaning easier calving for the daughter of the individual. Some of the factors that determine CEM are birth weight, calving ease and growth of the daughters.
SC (Scrotal Circumference): The SC EPD is the best predictor of fertility and is also associated with the age of puberty. The higher number at a younger age may indicate earlier puberty. SC is measured in centimeters. The SC EPD is adjusted to 365 days. In this genetic analysis theory, a multiple trait model was used for SC. WW and YW EPD were used as the predictor variable to increase the accuracy of SC EPD.
FAT (Rib Fat): Animals with low or negative FAT EPDs are expected to produce leaner progeny then those with higher FAT EPDs. This EPD measures fat thickness at the twelfth rib through ultrasound measurements at a year of age on live animals. These measurements have been shown to be highly correlated to actual back fat at harvest. All data is done through ultrasound scale. The more animals that data is collected from on a sire, the more accurate the EPD will be.
REA (Ribeye Area): This EPD is derived from ultrasound measurements of live cattle at a year and adjusted to 365 days of age. The REA EPD is measured in square inches, reflecting the area of the ribeye. Cattle with a higher REA EPD are expected to produce progeny that have higher red meat yield at harvest time. The carcass weight also reflects the yield at harvest time. The more animals that data is collected from on a sire, the more accurate the EPD.
IMF (Intramuscular Fat): This EPD is derived from the ultrasound measurement of the intramuscular fat in the ribeye, sometimes called marbling. Marbling is a term generally used on fat steers at harvest time. The data is collected on yearling bulls and adjusted to 365 days, a time period that on a bull correlates to fat steers at harvest. This EPD is read with the higher number indicating the progeny will have a higher quality grade at harvest.
BMI$ (Baldy Maternal Index): This index is for the commercial cow calf producer to maximize profit when Hereford bulls are used on British cross cows in a rotational crossbreeding program. This index assumes that the producer raises his own replacements and is retaining ownership of the balance of the calf crop through harvest, selling on a CHB grid. This index is an efficiency index that has a negative effect on too much milk. High milk will result in lower reproductive efficiency and require more nutrition for the cows. The CEM and CED are also used in this index, as live calves and less calving difficulty lead to increased fertility. This index also puts positive weight on WW and negative Weight on YW. This adds to the efficiency value of Hereford-sired cattle for the commercial cow calf producer
BII$ (Brahman Influence Index): This index is similar to the BMI$, with the primary difference being Hereford bulls are used in a rotational crossbreeding program on Brahman influenced cows rather than British cows. This index places more importance on fertility and the age of puberty, and less importance on growth and calving ease. This index has been designed to place more importance on traits where Brahman cattle may be more deficient.
CEZ$ (Calving EZ Index): This index is similar to the BMI$. This index is to measure efficiency and dollar value in the progeny of a Hereford bull when used by a commercial cow calf producer to breed yearling heifers. Compared to other indexes, the emphasis has been put on Calving Ease Direct and Calving Ease Maternal.
CHB$ (Certified Hereford Beef Index): This is a terminal sire index. This index represents Hereford bulls used on British cross cows with all progeny sold as retained ownership on a CHB grid. This index put emphasis on growth and all areas of carcass values.