There’s a running joke about geneticists that involves them weighting traits for indexes while sitting around a table drinking beer all day. However, the information that pertains to the creation of selection indexes is far more sophisticated than cracking open a PBR.
According to Greg Comstock, beef production strategic planning specialist, the beef industry has been successfully using index selection strategies for years through the calculation of certain expected progeny differences (EPDs).
“Yearling weight EPD is actually a biological index combining weaning weight and post-weaning gain EPDs,” he explains. “Similarly, yield grade EPD combines ribeye area, carcass weight and backfat EPDs, and maternal weaning weight (or total maternal) combines milk EPD plus the dam’s contribution to weaning weight EPD.”
While economic selection and biological indexes share similar strategies in combining traits, they differ when it comes to weighting them, Comstock says, in that traits are weighted according to their respective impact on profitability, and economic indexes are typically expressed in dollars per head or dollars per cow exposed instead of trait units.
However, “not all economic indexes are created equal,” Comstock explains. “Economic selection indexes vary in terms of which segment of the beef supply chain they apply to.”
Take the American Simmental Association’s All Purpose Index, for example. Economically relevant traits are balanced for the entire beef production enterprise — from birth to harvest. This type of index would be useful for producers retaining replacement females, and steers and culled heifers are fed and marketed on a carcass-merit-based grid.
On the other hand, there are indexes that focus on a narrower segment, such as the American Angus Association’s Grid Value Index. In this case, producers only interested in carcass grid merit can easily sort cattle to what fits their operation.
“Producers should utilize the index or indexes that best match their production environment, replacement strategy, breeds and market endpoint,” Comstock concludes.