This exciting new field will eventually provide tools for selecting breeding stock. It also may help answer questions breeders have regarding the tendency for certain animals to be hardier and more disease-resistant than others.

There may be breed differences, variations within a breed, and some appreciable differences in crossbred animals. Heterosis tends to boost hardiness and decrease susceptibility to disease.

The gene pool is diminished when a breed is established, selecting animals for certain traits and then breeding those animals to one another with no outcrosses. This is done to “stack” genetics so the animals always breed true, but it also narrows the genetic possibilities — including possibilities for maximum disease resistance.

Crossbreeding is a way to maximize not only feed efficiency, fertility, cow longevity, etc., but also disease resistance.

“We know disease resistance [and fertility] has relatively low heritability — around 10%,” Van Eenennaam explains. “When a trait has low heritability, it’s hard to improve on it from within-breed selections. Low-heritability traits are the ones that benefit most from heterosis. Thus, it stands to reason that crossbreeding would be beneficial for improving disease resistance. We certainly see this in terms of the overall health of crossbred animals,” she says.

Womack says the group’s studies will allow it to get closer to the reasons. “We’ve known for a long time that there is some heritability to disease resistance, but it’s been hard to get a finger on where and what the genes are,” he says.

Allison Van Eenennaam, BRD genetic researchVan Eenennaam says genetic selection starts with the cow-calf producer. While the feedlot industry is most dramatically affected by BRD, the cattle coming in are selected and bred by the cow-calf sector. It makes sense that ranches with a good track record for health will have a better market for their calves.

“If we can identify markers, and people start putting this into their selection decisions when breeding cattle, feedlots will prefer to buy those animals,” she says.  

Better diagnosis and treatment

Another component of the project consists of studying the pathogens — both bacteria and viruses — that researchers find in the test cattle, Womack says.

“There are six major pathogens associated with BRD. We don’t know which cause the disease and which tag along as opportunists to make things worse. We’re looking at these, and for unknown pathogens that may be hiding there somewhere,” he says.

Researchers want to determine if BRD in different parts of the country and different environments might originate with a different pathogen or set of pathogens. “Hopefully, we’ll come up with ways to help diagnose sick animals early, to determine which pathogens are there, and how they should be treated,” Womack says. Such information may lessen the dependence on antibiotic use in food animals.

The researchers emphasize that feedlot death losses from BRD, and its treatment costs, are huge expenses. It’s estimated that 10% of animals in feedlots will acquire BRD. “All those cattle — not just those that die — become a liability. They go off feed and have reduced weight gain,” Womack says. Profit on those animals drops dramatically; they take longer to get to finish weight, plus the treatment expense.

“If we can do more prevention, we won’t have to worry as much about antibiotic resistance, nor the high costs of treating the animals,” Neibergs says.

Genetic tests

The ultimate goal of the Bovine Respiratory Disease Complex Coordinated Agricultural Project is to develop genetic tests to enable producers to determine which animals might have more (or less) disease resistance. “We first need to validate these tests and make sure they actually work. We don’t know if these will be powerful enough to work well in multiple breeds, but that is our ultimate goal,” says Allison Van Eenennaam, University of California, Davis.

The beef project will be more challenging than dairy because there are more breeds involved, she says.

“We’ve found that a test that works well in one breed, like the Angus 50K from Zoetis, doesn’t work well in Herefords, for example. We’re hoping, since we are using the high-density 770,000 chip, that it will help with this, and identify markers that work well across breeds,” she adds.

Van Eenennaam is confident DNA testing is coming, and the price will drop. “It will probably be done on a larger scale because it can give us multiple pieces of information. If we can include disease resistance information, this would be an additional value from a DNA test besides parentage, genetic defects, genetic merit estimates for various production traits, etc.,” she says. 

Van Eenennaam says the project is looking to develop education materials for different sectors of the industry, with recommended management approaches to help minimize disease.

“The cow-calf producer plays a huge role in delivering animals to the feedlot to maximize their chances of a disease-free stint. There are usually some financial rewards, if the feedlot recognizes a producer is doing a good job,” she says.

Sifting the data

The project is generating millions of pieces of information. “We’re looking for genome-wide association studies. We look for consistent associations of a particular part of a genome. Hopefully, this will lead us to the genes responsible for the disease,” says Texas A&M University’s Jim Womack.

“The chips themselves may be useful for selective breeding of disease-resistant animals. These single-nucleotide polymorphisms [SNPs] are markers, and we can get as many as 800,000 of these on a single chip. The goal is to be able to tell from the markers which animals are resistant and which are susceptible to disease.

“Right now, we’re just looking at sick animals and comparing them with healthy animals, looking to find variances consistently associated with the sick or the well animals. Our preliminary data looks very promising, though it will be awhile before we start releasing data to the public,” Womack says.

Heather Smith Thomas is a rancher and freelance writer based in Salmon, ID.

 

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