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Composite bulls may trade predictability for simplicity.
July 9, 2012
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.
“I have 27 years of objective breeding decisions that harness the power of the AAA [American Angus Association] database,” says Brian McCulloh, Viroqua, Wis. The registered breeder, who makes 350 of those decisions each spring, says the predictive power is strengthened by the broad use of artificial insemination (AI) by Association members, who submit within-herd data that ties all animals together.
“Simply put, I am not comfortable ‘experimenting’ with data from other breeds to create a composite bull for our commercial customers. I have more confidence predicting the outcome of our pure line Angus bulls,” he says.
The Angus database updates weekly with more than 20 million performance measures and 17 million pedigrees. That data volume explains why, after dabbling in the composite market to try offering customers an outcross, McCulloh abruptly stopped.
Using the MARC across-breed EPD (expected progeny difference) adjustment factors help in comparing data, Callahan says. “But there is still a little bit of an unknown as to where that animal is going to come out.
“The purebred cattle evaluations give you better insight in terms of predictability of individuals and their offspring,” he says. Genomically-enhanced EPDs hone that ability. “You can make more progress – because you have greater access to performance information – than you can in most crossbreeding operations, unless they’re extremely well designed.”
To date, the DNA technology can only effectively sort out straightbred populations, he adds.
“That precludes it from being useful in composites and crossbreds,” Callahan says.
When selecting hybrids, commercial producers may face another challenge: “There’s an increasing need to purchase bulls in volume that provide both uniformity of calf crop and deliver on the various traits of interest,” Speer says. “Commercial bull buyers have access to larger sale offerings when shopping for Angus bulls compared to other breeds.”
Purchasing siblings in bulk is routine.
“That opportunity doesn’t exist when considering composite bulls,” he says.
Callahan doesn’t dispute the advantages of genetic diversity, but says he’s concerned with those who are “crossbreeding just for the sake of crossbreeding.”
His typical composite customer is in a terminal program, purchasing rather than raising replacement heifers. Otherwise, many have switched back to straightbreds.
“They really enjoy the uniformity of their calf crop and the predictability in their genetics,” he says.
There are no shortcuts to that.
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