Questions about the two tests initially came up when a WCVM graduate student was studying lung inflammation markers in normal horses.
"We started looking at what the expected ranges for two common tests – tracheal wash and bronchoalveolar lavage (BAL) – were supposed to be," explains Dr. Montgomery, an assistant professor in the WCVM's Department of Large Animal Clinical Sciences.
"In the course of the study, we came across several horses that looked clinically healthy, but their tracheal wash and BAL levels were — according to the current definition — not normal."
After much discussion and a review of published research, Montgomery and Lohmann concluded that although there are many expert opinions about reference ranges, there's a lack of sufficient studies done to establish those ranges.
Research has shown, for example, that similar tests in dogs show a different range of "normal" values based on the dog's age. This study will help to determine whether such age ranges are also needed in horses.
Variations due to geographic location are another unknown, so the study will help researchers establish a baseline for equine populations around the Saskatoon area.
The respiratory study, which starts in May, is funded through the WCVM's Equine Health Research Fund. The research team needs between 40 and 45 horses for the study with about 10 to 15 horses in each age group: young (one to three years), juvenile (three to seven years) and mature (seven years and up).
Horses volunteered for the study should have no history of chronic airway disease, no history of respiratory disease within the last six months and no clinical symptoms at the time of the study. To keep collected samples viable, horses must be within two to three hours' drive from the WCVM.
Montgomery says horses first undergo a basic physical examination (having their heart listened to and temperature taken) and a re-breathing test.
For the re-breathing test, clinicians have the horse breathe several breaths into a plastic bag — prompting the animal to take deeper breaths than it normally would. This allows the veterinarians to listen to the horse's lungs for signs of disease or other concerns. If any cause for concern is found at this stage, Montgomery says the research team won't proceed with further testing on the horse.
If all signs point to a normal, healthy animal, researchers will draw blood for a complete blood count and sedate the horse. With the horse sedated, a team member will insert an endoscope for the tracheal wash. Once the tube is passed into the horse's trachea, a small amount of fluid is deposited into the trachea and then sucked back up.
The BAL test is similar — a clinician inserts a tube through the horse's nose, down the airway and into the lung, where fluid is then deposited and re-collected.
Both the tracheal wash and the BAL are standard diagnostic tests regularly used by veterinarians, says Montgomery. The amount of fluid deposited is quite small and any fluid not regained in the procedure is absorbed by the horse.
"Normal horses usually do not get too distressed by the tests," says Montgomery. "But if a horse does get distressed, we will simply stop and not continue with the tests. In horses that are already suffering from, say, heaves (recurrent airway obstruction or RAO), the procedures can cause distress, which is another reason why we do a physical exam and re-breathing test before starting."
After samples are collected, team members will examine the blood work for any evidence of inflammation. Dr. Hilary Burgess, a veterinary clinical pathologist at the WCVM, is collaborating with Montgomery and Lohmann to do a cytological analysis of the tracheal wash and BAL samples. The samples will also be sent to the bacteriology lab at Prairie Diagnostic Services (Saskatchewan's provincial veterinary laboratory) to determine what types of bacteria may be present.
The study is a one-time analysis, and while the WCVM research team won't be re-testing horses at a later date, that's something researchers would like to do in future studies.
"In some ways it may be difficult to interpret results from the study," cautions Lohmann, an associate professor in the WCVM's Department of Large Animal Clinical Sciences. "On one hand, we should be able to say that all of the horses were clinically healthy, and if they fall outside of the recommended ranges, then perhaps those ranges need to be adjusted."
On the other hand, Lohmann says early disease changes are often subtle and may not be caught by clinical examinations — something that has the potential to affect results.
"There is also variability in results depending on how laboratories handle the samples and run the tests, so establishing a baseline for our collection practices and laboratory will be helpful."
Lohmann and Montgomery say their results will provide invaluable baseline information for future research projects. The study will also help them to identify the next steps for future investigations of equine airway diseases such as RAO.
More information about the study and its requirements for horses can be found on the WCVM's website.