Burt Ruthrford – Beef Magazine
I have a confession. I’m not good with numbers. So, let’s talk about numbers. Selection indexes, to be exact.
Actually, Matt Spangler is going to do the talking. Spangler is a beef geneticist at the University of Nebraska-Lincoln and one of the speakers at a King Ranch Institute for Ranch Management lectureship on genetics recently in Denver. In addition to KRIRM, the symposium was sponsored by the National Cattlemen’s Beef Association and Colorado State University.
How many of you have taken up a bull sale catalog and, with expected progeny difference (EPD) thresholds in mind, circled bulls you’re interested in and crossed out the bulls that don’t meet one or more of your baseline EPD levels? Probably everybody.
But, Spangler asks, how many good bulls did you pass by because they didn’t meet one of your EPD thresholds, but excelled in others? The guilty need not come forth.
That’s where an index comes in. Indexes are easy to use and interpret — and most importantly, are economically driven. Traits get more weight if they’re larger drivers of profit.
Indexes inherently account for the genetic relationships among traits as well. That’s good. It can also be very bad if you use the wrong index.
“If you think about growth traits — mature cow weight, birth weight, weaning weight, yearling weight Avoid wrecks in breeding season — they’re obviously not independent. These early traits are not independent of mature cow weight,” Spangler says. “
That means if I select to increase weaning weight and I also keep back replacement females, there is a tendency over time that the heifers I’d kept back are going to be larger in terms of mature cow size,” he says. “I have now pitted revenue, weight of calf at sale or weaning, against cost, which is increasing the cow size and increasing maintenance energy requirements.”
Can you select for multiple traits? “That’s what a selection index allows us to do.”
If you’re a terminal breeder, selecting an index like the Angus $Beef or $B is exactly what you should do. “But there’s a whole lot of commercial bull buyers that don’t fit that, but they still use $B to rank bulls they buy,” Spangler says.
“And it’s inappropriate because of replacement heifers. Dollar beef will put a lot of emphasis on carcass traits, carcass weight.
And so, as a consequence, the heifers they keep back will tend to be larger at maturity.” And because it’s a growth index, it doesn’t take into account female fertility. So, as you gear up for bull sales this fall, study those indexes carefully and know what traits they take into account. ❚❚