Airway Disease Studies

Researchers at Michigan State University are into their third year of a 10-year study of the pathogenesis and most efficacious treatments for chronic obstructive pulmonary disease (COPD). Explains Ed Robinson, MRCVS, PhD (respiratory physiology), Matilda R. Wilson Professor of Large Animal Clinical Sciences, "We’re interested in the lesser form of the disease, where horses at the racetrack and elsewhere have inflammation of their air passages that veterinarians can’t ascribe to a virus or to a bacterial infection."

During the past several years, researchers had been concentrating on the causes of airway obstruction in seriously affected horses and the accompanying muscle spasms in the wall of the airways. "But we’re moving away from that aspect, now," says Robinson, "and we are looking at mucous accumulation."

Questions being investigated include these:

  • Is the mucus produced in a horse affected with airway disease similar or different to the type produced in normal horses?
  • Is it more or less viscous?
  • Is it more or less difficult to clear from the air passages?
  • Why is it being produced?
  • If inflammation is relieved, will the mucus return to normal?
  • If the horses get repeated bouts of inflammation, will the mucus eventually change permanently so that it’s more difficult to clear?

Researchers have learned that horses seriously afflicted with heaves appear fairly normal when turned out to pasture, and although they have increased amounts of mucus in their air passages, its viscosity is normal and thus easy to clear. "But 24 hours after you put that horse in the stable, the mucus becomes viscous and very difficult to clear," Robinson explains. "We’re beginning to think that it has differences in the sugars that are associated with the mucus that make it more sticky.

"The question then is what’s going on with these less-affected horses? We have to look at this problem like we would in people: Many of us get extra mucus in our air passages when we go into a dirty environment, if we smoke, or if we get an infectious disease. But most of us survive those challenges for years without becoming respiratory cripples."

Robinson says that researchers think there probably is some sort of genetic tendency that places certain individuals—both humans and horses—at increased risk for developing serious respiratory disease when exposed to dirty or dusty environments.

Until recently, the tools needed to study mucus did not exist. "What we’ve done in the past three years is develop a method known as an ELISA (enzyme-linked immunosorbent assay) to quantify the mucus in the air passages," explains Robinson. "We’ve also worked with a laboratory in Canada where they measure the viscosity of mucus using very small samples."

By analyzing and compiling data from a large number of samples, Robinson hopes to determine if there always are changes that occur in mucus associated with inflammation. "If there are," he says, "then you can probably modify the inflammatory response in some way, either by modifying the horse’s environment or by using a corticosteroid or a more specific drug. This might prevent the mucous problem just by regulating the inflammation. If we know what’s happening to the mucus, maybe we can use specific drugs to modify the mucus to make it more clearable."—Marcia King

The horses participating in the study primarily will be those referred to MSU for poor performance, in addition to those coming in for non-respiratory problems (for control population purposes). The tools needed to gather mucus samples are too specialized for general veterinary use.

Additionally, researchers hope to investigate the families of horses which have a high incidence of heaves. Says Robinson, "If we knew a stallion threw a lot of horses with heaves and we could get some blood samples from those animals, it would be a great help. If we could find the target genes, we might be able to identify horses that have a susceptibility to airway inflammation."

"We’re just at the beginning of really studying mucus," Robinson reports. "We’ve got the tools, we’ve got some preliminary data, we’ve got a grant funded by the USDA to pursue this in more depth." A multi-million dollar endowment from the Matilda Wilson Fund covered the cost of the first three years of research.

About the Author

Marcia King

Marcia King is an award-winning freelance writer based in Ohio who specializes in equine, canine, and feline veterinary topics. She's schooled in hunt seat, dressage, and Western pleasure.

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