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DNA Tests Take on Cattle Disease

There are beef cattle DNA markers for growth rate, marbling, and even some maternal traits. 

But what about disease? Can a drop of blood or a hair follicle tell you if one animal is more resistant to disease than another? 

Probably, says a group of animal geneticists from around the country involved in a long-term USDA-funded study on that subject. They’re identifying DNA markers for resistance to bovine respiratory disease (BRD), the shipping and comingling scourge that costs about $1 billion a year in feedlot losses.

Alison Van Eenennaam, animal geneticist at the University of California-Davis, is a collaborator on the project. She says 1.4% of feedlot cattle die before harvest, many of them from BRD. “That number hasn’t changed in 30 years,” she says in support of the genetic research. 

It’s worth trying to find BRD-resistant animals, she explains, because at least 16% of cattle and calves will have it at some point in their lives. “One study says that each BRD-infected steer costs the producer $254,” she says. 

The project researchers believe genetic resistance could be cheaper than treating BRD with antibiotics, and it also could help address consumer demands for fewer drugs in animal production.

Disease resistance happens to be a relatively low heritability trait at around 20% (80% of the variability is caused by environmental factors). That makes it tougher to sort out the genes that control it, compared with growth and marbling traits, she says. 

The research partnered with two cooperating commercial feedlots to identify sick animals and to compare their genes to healthy pen mates. They trained cattle handlers to use objective measures to identify BRD-infected animals – strict criteria for rectal temperature, nasal discharge, coughing, eye drainage, and head disposition. 

After running the DNA blood tests on thousands of sick and healthy animals, they can see some patterns of genes and gene clusters that are common to both groups. Then they correlate that back to specific bulls and see that some tend to sire more calves with the BRD-resistant genes. 

“It won’t be a bullet-proof predictor of resistance, but it will enable the selection of cattle that are a little less likely to get sick,” Van Eenennaam says.

One encouraging fact is that the dairy industry has had some success using genetics to reduce mastitis. The pork industry has done the same in selecting for pigs that are less susceptible to a disease called PRRS. 

Q&A with alison van eenennaam

SF: When will the genetic test for BRD resistance be available to producers?

AV: No guarantees, but within five years, I hope.

SF: Is it just one gene that determines this?

AV: No. There are likely a large number of genes, probably thousands in total. What we hope to do is identify large-effect genes for this trait. If we can identify genes that are responsible for 20% of the genetic variability in this trait, we can probably make genetic progress. 

SF: Is it possible that the genes that give BRD resistance could also give resistance to other diseases?

AV: We don’t have anything to prove that yet, but it is possible. I get that question from veterinarians a lot. It is possible we will select for animals with improved immune function. Ideally, in selecting for animals that are not getting sick, we are also selecting for better performing animals. If they aren’t suffering from BRD, they can put that energy into growth.

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