Bovine respiratory disease (BRD), also called pneumonia or shipping fever, is costly for the U.S. cattle industry with more than a million animals lost annually. With the stress of weaning, marketing, transporting and receiving cattle in a new home, the question isn’t why do some of them get sick. The question is this: Why don’t they all get sick?

That’s because some cattle have stronger immune systems and less illness; disease resistance is partly genetic. Genetic research is giving us tools to select for (and against) certain traits in cattle, and several studies have been looking into genetic approaches to select for cattle that are less susceptible to disease.

One extensive project included researchers at Texas A&M, Washington State University, University of California-Davis, New Mexico State University, Colorado State University, USDA Agricultural Research Service and Geneseek.

This research utilized large populations of animals that got sick with BRD, and control groups that had the same exposure and did not get sick says Alison Van Eenennaam, professor of animal genomics and biotechnology at UC-Davis.

Genetic connection

“We genotyped those animals, looking at DNA markers in the genomes of those two groups. We wanted to see if some markers only show up (or more frequently show up) in the group that didn’t get sick, or in the group that got sick—looking for the ones that are less susceptible to BRD. Eventually breeders might be able to incorporate this knowledge into selection decisions, raising animals that won’t get sick as often.”

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It would still be necessary to use management strategies to minimize incidence of BRD (vaccinate cattle, handle them with less stress, etc.) but genetic knowledge would provide one more tool to decrease problems and reduce antibiotic use.

Genetic selection starts with seedstock breeders and cow-calf producers. Feedlots are affected most dramatically by BRD, but the cattle coming in—whether they are disease resistant or not—were selected and bred by the cow-calf sector. 

“BRD is a big problem; about 1% of feedlot animals don’t make it to finish. This is a huge loss. These cattle have lived through birth, calfhood stresses, etc. and should not be perishing at feedlot age. If we can make BRD a less prominent disease, this would be very beneficial for the industry,” she says.

Research challenges

The genetic project involved both beef and dairy cattle. The beef side is more challenging, with more breeds involved. 

“We found that if you develop a test that works well in one breed, like the Angus 50K that Zoetis has, the Angus prediction equation doesn’t work well in a different breed.  We’re hoping, since we are using the high-density 770,000 chip, that it will help identify markers that work well across breeds, but this will be more difficult,” Van Eenennaam says.

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“There are also multiple genes involved. The success we’ve had as it relates to selecting animals has been more of a genomic selection approach, with very large data sets in one breed, such as Holstein.” 

There are many beef breeds, however, and it’s difficult to get sufficient data—even in Angus, the largest breed—to develop accurate predictions for diseases. That’s especially true for something like BRD, since you may not know how the animals you selected and raised perform in the feedlot if you don’t retain ownership.

“We don’t have a silver bullet for producers. The research was done, and various small-effect gene locations identified, but none are sufficient to create a commercial genetic test,” says Van Eenennaam. Through this process, however, researchers learned more about the inheritance of disease susceptibility or resistance.

“The trait of getting sick with BRD is heritable. Just like mastitis, there is a genetic element. It’s not hugely heritable, but if we had some good indicator traits we could select animals that are less susceptible to disease. We need records in the database of each breed association,” she says.  Some breeds are working on this.

“Simplot has their own cattle population, owned from birth to slaughter, and record how those animals perform in the feedlot. They incorporated BRD into their selection index and are now selecting animals whose offspring are less susceptible to this disease. 

“In a situation like that, with a single breed (in this case, use of a terminal breed, with Charolais sires), and records, you can match genomics and records to make your selections, and make it work,” she says.

Production challenges

The challenge with making it work across the entire beef industry is the many breeds and individual operations involved, and lack of information coming back from the feedlot to breed associations.

This is a problem with many traits in beef cattle because we don’t have records coming back to the producer on feed efficiency or anything else. “It’s not impossible to select for animals that are less susceptible to disease; it’s just that you need these records.”

Commercial cattlemen can gain genetic resistance to disease by crossbreeding. This is the simplest way to genetically improve cattle health, creating animals with stronger immune systems.

Heterosis is the best tool we currently have for improving fertility, health, and longevity in cattle.  “There are still many commercial operations utilizing just one breed and not taking advantage of crossbreeding,” she says.

 Feedlots bear the brunt of BRD problems but don’t have much control over genetic selection unless they own the animals from start to finish. “There is a lot we can do to improve the health of feedlot cattle in the absence of accurate genetic tests, however,” she says.

“We can crossbreed, vaccinate, wean before they get on the truck, and background those cattle. Those four things would probably do more to take care of the BRD problems than anything we can do with a genetic marker!” 

Smith Thomas is a rancher and freelance writer based in Salmon, Idaho. The opinions of the author are not necessarily those of beefmagazine.com or Farm Progress.