Studying the airway microbiome in horses

WCVM researchers performed endoscopies to collect information and samples from horses’ respiratory tracts. Photo: Jordan Steedman.

Veterinary researchers at the Western College of Veterinary Medicine (WCVM) are investigating whether certain bacterial populations in a horse’s windpipe can contribute to a respiratory disease called recurrent airway obstruction (RAO).

More commonly known as heaves, RAO can be triggered by something as simple as feeding poor quality hay to a horse. Exposure to dust, mouldy hay, ammonia fumes and fungal spores in the environment can aggravate the condition. While owners can generally manage a horse diagnosed with RAO, it can end a high-performance animal’s career.

The common chronic inflammatory airway disease is frequently compared to asthma in humans since horses with RAO often develop the symptoms seen in asthma sufferers: wheezing, coughing, and exercise intolerance.

Motivated by human research on asthma and chronic obstructive pulmonary disease (COPD), large animal internal medicine specialist Dr. Katharina Lohmann has developed the airway microbiome project.

She and associate professor Dr. Julia Montgomery are investigating the bacterial populations (microbiomes) that inhabit the trachea (windpipe) of both healthy horses and horses with RAO.

It’s the first study of its kind and builds on an earlier research project by Montgomery in which she performed airway diagnostics in healthy horses. She was able to establish normal reference ranges for the tests currently used to diagnose equine airway disease, particularly RAO.

“This is really the first step,” says Montgomery. “No one has ever looked at these basic questions before. What kind of bacteria are there in the airway of horses? Are there different profiles that we can discern for healthy and sick horses?

“If there are distinct groups, then that might help us down the road to identify at-risk horses sooner and potentially improve their clinical outcome.”

The study includes results from 12 healthy horses and 12 horses diagnosed with RAO. To obtain samples, the WCVM researchers sedated each horse before inserting a video endoscope into the animal’s windpipe. The endoscope allowed team members to visualize the upper respiratory tract for conformation defects, grade the amount of mucus in the windpipe and facilitate sample collection.

Next, the researchers injected fluid through a small port in the endoscope and then used a syringe to collect fluid, mucus and bacteria from the windpipe. This sample is used to establish profiles of bacterial populations living in the airways for the microbiome analysis.

Finally, researchers passed a second longer tube through the horse’s nose into its lungs. They injected a larger amount of fluid into the lungs and then used multiple syringes to draw back a sample. The research team analyzed this sample for its cellular composition so they could establish or confirm a diagnosis of RAO — or determine airway health in the healthy horses that were enrolled in the study.

In her earlier project, Montgomery was intrigued to see that almost all of the samples showed the presence of bacteria in the airway. Like any other part of the body that has direct contact to the outside world, the airway is not sterile, and bacteria are part of the normal flora, just as they are in the gut.

However, no one in human or veterinary medicine has yet determined exactly how these bacteria contribute to both airway health and disease.

The researchers hope they can identify more effective treatments and management strategies by unravelling the potential role that bacteria play in airway disease and gaining a better understanding of how horses develop RAO.

“One thing that has always interested me is the different outcomes we see in horses with heaves,” says Montgomery. “Why do some respond to treatment and others do not? Why do some respond to environmental management and others do not?”

A diagnosis of RAO may seem daunting to horse owners, but Montgomery finds that most people can successfully adapt their management regimes to ensure their horses’ continued health and well-being.

“The biggest challenge that people with newly diagnosed animals face is to implement the recommendations that we give them,” says Montgomery.

“Once they can control the horse, maybe initially with drugs, and then with environmental management, most horse owners do really well. So long as it is within their means, they’re willing to do whatever is necessary to ensure the comfort of their animal.”

Jordan Steedman of Canmore, Alta., is a third-year veterinary student who was part of the WCVM’s Undergraduate Summer Research and Leadership program in 2014. Jordan’s story is part of a series of articles written by WCVM summer research students.