Utilizing Multi-Trait Index EPDs

Livestock Update, December 2006

Scott P. Greiner, Extension Animal Scientist, Beef, Virginia Tech..

A successful beef enterprise is contingent upon the integrated management of genetics, nutrition, health, marketing, and finances.  From a genetic perspective, the industry has worked hard to identify and develop prediction tools (EPDs) for a large number of economically important traits.  As a result, many breeds now offer in excess of 20 traits for which EPDs are available.  It is well recognized that effective sire selection involves identification of bulls which balance a multiple number of these traits.  Consequently, it can become a daunting challenge to identifying which EPD traits (among the many) are most critical, as well as prioritize and place proper weighting as to their importance for even the most basic of bull selection schemes.

For these reasons, multi-trait selection indexes have been developed by the beef industry.  These indexes allow for selection for several traits simultaneously.  For each trait contained in the index, both genetic and economic values are considered, and the end result is a comprehensive genetic prediction value that represents overall economic merit of the animal.  The strategy of these multi-trait EPD indexes is to provide simplicity and convenience to selection decisions by allowing for selection based on one index EPD value rather than several individual component EPDs.  Multi-trait index EPDs differ from individual trait EPDs in that they are expressed in economic terms, meaning they predict differences in progeny performance in dollars rather than in pounds or other performance indicators.  This is accomplished by assigning economic weightings to the component EPDs of the index, and by using a set of assumptions which impact estimated revenue and costs for impacted traits.

A number of selection indexes have been developed by beef breed associations.  The following will examine a few of these indexes and provide a short description of each.

Angus $B (Beef Value) - $B is a multi-trait genetic selection index for both feedlot performance and carcass merit.  Specifically, $B represents the expected average dollar-per-head difference in progeny post-weaning performance and carcass value compared to progeny of other sires.  In calculating $B, expected carcass weight and its value are calculated, along with production cost differences.  $B is composed of two other multi-trait index EPDs - $F and $G.  $B is not simply the sum of $F and $G, as adjustments are made to avoid double-counting weight between feedlot and carcass segments.

Angus $F (Feedlot Value) - The $F value is the expected average difference in progeny post-weaning feedlot performance compared to progeny of other sires.  $F is expressed in dollars per head and incorporates weaning weight and yearling weight EPDs.  Typical feedlot gain value, feed consumption and cost differences are accounted for in the final calculations, along with a standard set of industry values for days on feed, ration costs and cash cattle price.

Angus $G (Grid Value) - $G value is the expected average difference in progeny performance for carcass grid merit compared to progeny of other sires.  The $G index combines quality and yield grade factors, and is calculated for animals with carcass EPDs, ultrasound EPDs, or both.  A three-year rolling average is used to establish typical industry economic values for quality grade and yield grade (premiums for Prime, CAB and Choice carcasses, as well as YG 1 and 2; discounts for Select and Standard quality grades, and discounts for YG 4 and YG 5).  $G is also expressed in dollars per head.

Charolais Terminal Sire Index - Ranks sires based on their genetic merit for post-weaning performance and carcass merit.  The Charolais Terminal Sire Profitability Index utilizes an interactive on-line tool generate dollar indexes per specific inputs provided by the user.  Inputs include weaning weight, projected ADG for backgrounding/grower/finishing phases, live prices, and carcass premiums/discounts.  In this manner, the TSI can be calculated to fit the needs of each individual operation.

Gelbvieh Grid Merit EPD - The Grid Merit EPD measures the dollar value associated with marketing progeny on a value-based carcass merit grid.  Specifically, the Grid Merit EPD predicts the carcass value associated with selling carcasses on a grid based on quality grade, yield grade and fitting weight specifications.

Gelbvieh Feedlot Merit EPD - The Feedlot Merit EPD measures the dollar value associated with the expected gain and feedlot efficiency of progeny when fed in a typical feedlot arrangement.

Hereford Certified Hereford Beef Index - A terminal sire index, where Hereford bulls are mated to British-cross cows and all offspring are sold as fed cattle on a CHB grid.

Simmental Terminal Index - Evaluates sires for use on mature Angus cows with all offspring put on feed and sold grade and yield.

Angus Weaned Calf Value Index - Predicts the expected average difference in progeny preweaning value in dollars per head.  Provides way to compare sire impact on cow-calf herd based on his maternal and growth contributions.  Incorporates EPDs for birth weight, weaning weight, milk, mature weight, yearling weight and mature height.

Hereford Baldy Maternal Index - Index designed for commercial cow-calf producers who use Hereford bulls in rotational crossbreeding programs on Angus-based cows and heifers.  Retained ownership of calves through the feedlot phase of production is assumed, with fed cattle marketed on a Certified Hereford Beef pricing grid.

Hereford Calving EZ Index - Similar to Hereford Baldy Maternal Index, except that Hereford bulls are mated only to yearling heifers.  This index has more emphasis on direct and maternal calving ease.

Simmental All-Purpose Index - Evaluates sires for use on the entire cow herd (bred to both Angus first-calf heifers and mature cows) with the portion of their daughters required to maintain herd size retained and the remaining heifers and steers put on feed and sold grade and yield.

Interpretation of index values in bull selection is very similar to using EPDs.  For example, a $10 difference in Angus $B value between two bulls would indicate an average of $10 difference in progeny profitability when the calves are fed post-weaning and marketed on a carcass value grid.  The relative difference between animals is of most interest.

So how can these index EPDs assist us in bull selection?  The index values can be very useful, particularly for traits associated with carcass merit.  The immediate importance of carcass merit for an individual herd will largely be dependent on an operation’s marketing scheme (retained ownership vs. selling feeder cattle), current genetics, management, and other factors.  However, a common challenge for all producers is placing proper selection emphasis on the individual carcass trait EPDs that are available (marbling, REA, fat thickness, weight).  The advantage of index EPDs is that they combine the effects of these several carcass EPDs and put them into one understandable, easy to interpret value.  By using industry averages for premiums/discounts and costs of production, the individual EPDs that comprise the index are weighted accordingly.

There are some challenges to using these indexes that have been discussed here.  These post-weaning/carcass indexes are terminal sire indexes, and are intended as predictors of slaughter progeny performance.  They should not be used as the sole selection tool for producing replacement females, as they do not consider maternal genetics.

In summary, these new index EPDs offer great opportunity to enhance balanced-trait selection.  As an example, currently carcass traits carry significantly less importance economically compared to reproduction and growth for many cow-calf producers.  However, genetic merit for carcass merit is becoming increasingly important for all producers - even those currently not retaining ownership.  Consequently, carcass traits need attention in today’s selection programs so that producers may position themselves for the future.  With these multi-trait index EPDs, that process has been simplified.

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