Depending on how you look at it, a bull-sale catalog is either packed with useful information or as confusing as a poorly translated instruction manual for a made-in-China entertainment center.
Development and application of expected progeny differences (EPDs) over the past 30 years, and more recently the incorporation of genomic predictions, have enabled dramatic progress in genetic selection.
However, the complexity of sorting through the growing list of EPDs can be daunting for many bull-sale customers. Also, a list of EPDs offers a temptation for ranchers to focus too much on one or two traits, gradually shifting the genetic makeup of their cow herds into undesirable territory.
That is where the selection index comes in. Virtually all the major breed associations now use at least one selection index, which combines a weighted list of EPDs for economically important traits to calculate a single rating, based on revenue potential, for comparing bulls.
Seedstock producer Willie Altenburg, of Altenburg Super Baldy Ranch in northern Colorado, believes strongly in the use of indexes. Producers often do not have the time or inclination to evaluate all the EPDs available on bulls or AI sires, he says.
Altenburg, who also serves as associate vice president of beef marketing for Genex cooperative, adds that an index, by definition, encourages multitrait selection. Indexes can help ranchers work toward specific genetic goals based on their production and marketing systems. He stresses, however, that bull buyers need to understand the index and know its limitations.
University of Nebraska animal scientist and geneticist Matt Spangler, PhD, says using an index helps mitigate the cumbersome nature of multi-trait selection and allows selection of bulls based on projected revenue or profit, at least to some extent. They do so by combining multiple EPDs, each weighted by an economic value, into one numeric value often expressed in dollars per animal. Along with “output” measures such as growth and carcass traits, an index also can include EPDs related to “inputs,” such as feed intake, that play a major role in profitability.
Applied properly, economic indexes are powerful tools for selecting cattle based on their potential to generate revenue, Spangler says. Ranchers need, however, to understand the underlying assumptions within an index before applying it toward their genetic selection.
Breed toward a goal
Spangler stresses that different indexes include different traits and associate different economic values with them. So, you must evaluate indexes based on traits you intend to emphasize in your herd. He adds that economic indexes allow for superiority in one trait to offset average or below-average performance in other traits. A sire with an above-average index value may not be above average for all its component EPDs but is superior in one that is weighted heavily. Also, the accuracy values associated with EPDs in an index influence how accurate the index will be.