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New Genetic Tool Helps Harness Heterosis

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2. Two-Breed Rotation System. Conducted in two breeding pastures, or sequentially, the two-breed rotation may be easier to deploy. It won’t bring as much heterosis to a program, though. Weaber says it produces 67% of the heterosis of an F1-terminal sire system.

3. Composite Bull System. In this scenario, the producer uses a two-breed composite bull. When mated to the same type of female, the system retains 50% of the heterosis of the F1-terminal sire system. This is as simple as straight breeding. No separate mating pastures or herd groups are required. This may be optimal for small herds or where labor and management are constrained.

In choosing between the systems, Weaber says producers should consider breeds in the herd to get complementarity. Also, factor in whether one purchases or raises replacements, what the marketing end point is and what the environmental and management limitations are. These last two points consider things like mature weights, lactation potential and even tagging and sorting.

“There’s no one-size-fits-all solution,” Weaber emphasizes. “Each herd has a set of systems that may make sense to deploy and others that wouldn’t achieve production goals.”

DNA MEASURE OF HETEROSIS

As efforts to maximize hybrid vigor in commercial herds continue, a new genetic tool, Envigor, has just been released in the U.S. to measure heterosis levels in individual animals.

Part of a genetic ranking system, this test, by Neogen’s Igenity Beef, can score hybrid vigor alone or in combination with already-existing tests for parentage and additive genetic variance (heritable traits).

Envigor’s genesis is in a Canadian company, Delta Genomics, purchased by Neogen in January 2019. Delta Genomics developed and released a DNA test for beef cattle in 2017, described as a three-in-one product. It used DNA to show parentage on a calf and to calculate hybrid vigor. It is now part of the Igenity Beef system.

Stewart Bauck, vice president of agrigenomics at Neogen Corp., predicts commercial producers will be heavy users of this new heterosis measurement tool. He’s convinced the company has developed a truly balanced index that can give commercial producers not only a score for heterosis on an animal but the additive genetic components, as well.

Until now, Bauck explains, genetic testing for commercial cattle focused on the additive genetic variance, or the heritable genetic component, of the equation. “We use that tool not only to select the female for what will genetically positively impact her performance but also for those genes she will favorably transmit to the next generation. We call that the ‘additive genetic variance.’ It is adding something.”

In addition, there has been the parentage test, key in knowing which calves are coming out of which bull and how much each contributes to the genetics of a herd.

“Some bulls are much more active than others,” Bauck explains. “About 10 years ago, researchers looked at eight yearling bulls, and they found that two of the eight bred over 20 heifers in a limited season. Two of those bulls bred four heifers each. So, there was a huge disparity. We don’t want to keep replacements out of low-serving capacity bulls—so we can test parentage.”

With parentage and additive genetic variance firmly entrenched in the genetic capabilities of the commercial side of the cattle business, Bauck, like Weaber, says the heterosis side has been more challenging.

“The problem is you get heterosis in that F1, that first generation, but not in the next. There is this conflict. Commercial producers set up crossbreeding to capitalize on heterosis, but that turns counter to a lot of the things they want to do from the additive perspective. It’s a numbers game.”

He goes on to explain that as a commercial producer who is using crossbreeding starts to select for additive traits, the benefits of heterosis are often lost in the stable cross.

“Just because it’s a stable cross (Santa Gertrudis, Beefmaster, Brangus, etc.) does not guarantee you have hybrid vigor,” he says. He points to Brangus as a breed where through the selection for specific traits, specifically a focus on carcass traits, the Angus alleles have been stacked.

An allele is one of the possible forms of a gene. Most genes have two alleles, a dominant and a recessive. If a cow has both a dominant and recessive allele (heterozygous for that trait), she will express the dominant trait.

“In other words, over time, she becomes more like an Angus than a Brahman. You lose the very things you are trying to get with heterosis—fitness, disease resistance, tolerance to parasites, suitability for southern climates. You are removing Brahman alleles and replacing them with Angus as you select for those Angus-dominant traits.”

RANKING HYBRID VIGOR

This is where a tool to calculate heterosis genetically can offset the natural tendency to breed the hybrid vigor out of a herd. Bauck says Envigor scores hybrid vigor. It can be used along

with profiles on parentage and additive genetic

variance to identify superior productive replacement females.

Jamie Courter, product manager for Envigor, says it all sounds complicated, but it’s user-friendly and easy.

“First, this is a weighted index, which is what Igenity users are accustomed to. Producers look at the Igenity total cow index, a maternal trait index, to help them make replacement choices based on individual needs and desires for herd development,” she explains.

“Now, in addition to this maternal index, we have introduced Envigor, which is a 1 to 10 ranking of hybrid vigor,” Courter adds. “Taken together, these two are a total package where one side complements the other.”

Bauck says for the small segment of commercial producers who want a lot of detail, an online dashboard continues to be available where they can build a custom sorting index. Most producers, however, want a simple sorting tool. For them, predesigned maternal indexes will rank heifers from top to bottom based on areas of emphasis.

“The goal is for that commercial cattle producer to be able to easily select replacement females that will stay in the herd a long time and make them money,” he notes.

Pricing for Envigor is $20 ordered alone. If added to the full Igenity profile, which costs $29, Envigor is just $5 more, for a total price on the full package (Envigor plus Igenity) of $34.

Courter adds research shows that with a 1-score increase on Envigor’s 1 to 10 scale for heterosis, a replacement has a 4% increase in the probability she will breed as a yearling. Also, there is a 4% increase she will stay in the herd for 6 years and a 2% decrease in the probability of her having a health event.

(CC/AG)

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