Shorthorn Association

Using EPDs For Selection

Calving Ease Direct (CE, DIR) The most important EPD in sire selection for use on heifers is Calving Ease Direct. As the name implies, this measure predicts the ability of a sire to produce calves that come out easily, without assistance. Expressed as a percent of unassisted births, the more positive numbers are the more desirable. For example, a bull with a CE of -2.5 is expected to sire 4.0% more assisted births than a bull with a CE, DIR of +1.5 (1.5 plus -2.5 = 4.0). Put simply, if the bull with a +1.5 CE, DIR EPD sires 100 calves and 1 birth requires assistance, then the example bull should sire 5 calves that need assistance at birth.

Calving Ease Maternal (CEM, DTRS) If you plan to retain daughters from a particular bull, then Calving Ease Maternal EPD becomes more of a priority. This measure often has an inverse relationship to Calving Ease Direct. Cattle breeding logic tells us that when calves come easier, the natural pelvic area of the females may also get smaller. As a result, daughters from a sire known for Calving Ease may be less desirable due to this antagonism. Maternal Calving Ease is basically one generation further than Calving Ease Direct. Expressed as a percent of unassisted births, CEM reflects a bull's ability to sire daughters that calve unassisted. As a result, a more positive number is more desirable. Although CE, DIR and CEM, DTRS values tend to be antagonistic, a bull that is positive for both CE and CEM should be given strong consideration if one wants to market bulls suitable for use on first-calf heifers and sell or retain replacement females that can calve on their own.

Birth Weight (BW) This trait needs little introduction, but the emphasis on Birth Weight can be overdone. At the most basic level, Birth Weight is nothing more than an indicator trait for calving ease. For decades, the weight of a calf at birth was the only hard number collected by breeders to tell bull buyers what they could expect at calving time. Economically, over-selecting for low birth weights can take us in the wrong direction; cattle still sell by the pound. The most important figure is the number of live calves that hit the ground with no assistance from a ranch hand. Still, threshold values for BW are on the minds of many bull and female buyers. In the Shorthorn breed, bulls suitable for use on heifers need to be significantly less than breed average. Use BW EPD in conjunction with Calving Ease Direct (CE). Phenotypic traits like length of body, shoulder design, head shape, circumference of bone, and even frame score play a significant role in determining birth weight and calving ease.

Weaning Weight (WW) Put simply, weaning weight is the ability of a bull's calf to dry off, stagger to its feet, and grow like mad. By itself, Weaning Weight EPD has limited use, merely pounds of calves attributed to the sire or dam of interest. However, when used in conjunction with other traits (CEM, BW, YW, & Carcass), WW gets much more significant. Within the 2009 sire summary, the top 5% of the Shorthorn breed should wean calves approximately 23.9 lbs. heavier on average than the bottom 5% of the breed. More importantly, bulls within the sire summary that may have identical WW EPDs can be drastically different for traits like CE and Carcass Marbling. As a result, finding a sire with a strong WW that also excels in other economically relevant traits important to your breeding program is a key element to success.

Milk The dairy industry measures the success of a cow in pounds of milk produced and the nutritional attributes or fat content of the milk. Research has shown that the nutritional quality of milk offered by a beef cow is just as important as the amount produced in generating heavier calves. Since beef cattle breeders don't milk our cows, success is measured in pounds of calf attributed to milk at weaning. A bull's Milk EPD is determined by his daughter's ability to wean heavier calves than her contemporaries. Just because a cow weans the heaviest calf every year, does not necessarily mean her Milk EPD should be the highest in the herd. The performance of her calf could be attributed to the dam's or sire's growth genetics or a number of other environmental factors eliminated in the EPD calculation (age of dam, birth date, etc.). Shorthorn breed average Milk EPD (sires) is +2.4. In environments with severely limited feed resources, Milk EPD can be too high, having a negative impact on rebreeding rate. However, in most cases, keep moving Milk EPD in a positive direction.

Total Maternal (TMat, TOTM) Mathematically, Total Maternal EPD is nothing more than 1/2 of WW plus Milk EPD. For example, the 2009 Sire Summary has breed average (sires) WW at +13.4 and Milk at +2.4. If you take 1/2 of 13.4 (6.7) and add 2.4, you land at breed average (sires) TMat (TOTM) of +9.1. This trait simplifies the process of selecting a bull to produce replacement females by using one number that expresses a cow's ability to bring in a heavier calf.

Yearling Weight (YW) Yearling Weight EPD has long been the "end all" measure of performance. However, single-trait selection for YW can lead to far more serious problems, especially at they relate to bottom-line profit. Mature size or frame score must be monitored when selecting a bull for performance via YW EPD. Cow maintenance costs, calving difficulty, and even breeding problems can result. In other words, a mature bull that weighs 2,700 pounds cannot naturally breed an 800-pound yearling heifer. As you select bulls that exceed breed average YW of +22.3, be careful of CE, BW, and WW. You may talk yourself into a very labor intensive calving season and more expensive feed bill.

Carcass Weight (Cwt) Carcass Weight EPDs are expressed in pounds as a predictor of the differences in hot carcass weight of a sire's progeny compared to progeny of other sires. If two bulls were bred to comparable groups of cows, the average carcass weights at a given age of the resulting offspring of each sire would differ by the amount of difference in the Cwt EPDs of the two bulls. They are tools that are good predictors of TOTAL retail product but are not good predictors of PERCENT retail product. They can be used to help genetically design carcasses with weights which fall within an acceptable industry weight range.

Marbling Score (MB) Subjective evaluations of intramuscular fat in the ribeye are expressed as Marbling Scores in numeric units of the USDA marbling score. Higher values indicate genetics for greater deposition of intramuscular fat or higher expected marbling scores and higher USDA quality grades at a constant age. Higher marbling scores are generally favored over lower values because choice grade carcasses are usually more valuable than those with USDA quality grades of select or lower if all other carcass characteristics are similar. Marbling scores are, however, impacted considerably by nutrition and environment.

Backfat (BF) Measured between the 12th and 13th ribs and expressed in inches, Fat Thickness EPDs can be used to predict one sire's progeny compared to another sire for differences in external fat at the measurement point. Minimums in fat thickness are necessary to protect carcasses from cooler shrink. Ability to maintain body fat reserves are important factors in maintaining normal productive physiological processes such as reproduction. Fat thickness does have a negative genetic relationship to percent retail product.

Ribeye Area (REA) Ribeye area EPDs are expressed in units of square inches measured at the 12th rib and offer an objective measurement of genetic differences in muscularity. Larger values for ribeye area are indicators of an expected increase in total carcass muscle which in turn can account for a significant amount of the variation in percent retail product.

Percent Retail Product (%RP) The Percent Retail Product EPD combines traditional carcass traits (fat thickness, percent kidney, pelvic and heart fat (%KPH), hot carcass weight and ribeye area) into a composite EPD.

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