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Crossbred Bull 'Fix'

July 9, 2012
 
 

By Miranda Reiman, Certified Angus Beef

A good crossbreeding program takes some background in genetics, a big enough herd and land base, good bull suppliers and time to figure all that out. Producers looking for a simpler route to heterosis often opt to use a composite bull.

"In order for a crossbreeding operation to maximize heterosis, it takes a lot of different pasture, a lot of management, which because of size and time a lot of people can’t devote to it," says Jarold Callahan, president of Express Ranches, Yukon, Okla. "You basically have to have different herds within your herd."

So the composite bull market was born, where breeding stock is billed as already having that built-in hybrid vigor.

"Implementing crossbreeding can be somewhat daunting," says Nevil Speer, Western Kentucky University animal scientist. "Many operations would rather forgo such effort if production can be maintained while also ensuring relative absence of problems. As a result, producers are often encouraged to utilize composite bulls as a simplified means to boost heterosis and subsequent production."

But Callahan says it’s not always a "quick fix." Express has sold hundreds of Limousin-Angus crosses over the years, but recently decreased the number of composites (F1) offered on an annual basis.

"A lot of people we sent F1 bulls to were very disappointed because of gene segregation and what was being transmitted from each parent," he says. "Some progeny of these bulls really favored traits of one breed and some favored traits of the other, some looked Angus and some looked Continental. You ended up with a set of calves that were not only visually different, but a lot different in terms of outcome and how you needed to manage them."

Geneticist Bob Weaber, Kansas State University, says that’s partly because what works on average for the whole calf crop varies among individuals. That may shift the balance of traits toward one breed or the other.

"Even though the F2s [composite progeny] have half of their genetic material from each breed on average, some re-pairing of chromosomes from the same breed occurs," he says. "When we make an F2 we see a decrease in heterosis, because on average one-half of the animals’ chromosomes consist of pairings from the same breed of founder."

Data from the U.S. Meat Animal Research Center (MARC) suggests that the progeny from matings of F1 parents are no more variable than either of their purebred founder breeds for traits like weaning weight or yearling weight. However, for traits controlled by a single gene, these progeny are noticeably less consistent than the F1 parents, especially if the founder breeders were very divergent, Weaber says.

Speer says that makes it hard to measure how much productivity they should add to the herd: "In many instances composite bulls actually represent backcrossing and may reduce heterosis potential versus using a breed that serves as a total outcross."

From a seedstock producer’s perspective, it can be much more difficult to create a reliable composite compared to a purebred bull.

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