If your vet suspects an issue with your horse’s airways, or if your horse is not performing as expected, he or she can perform a tracheal wash using an endoscope – a long tube through which a small amount of liquid is flushed into the trachea and then sucked back into a syringe, which is then submitted to our lab. This liquid now contains cells from the trachea (the tube that leads to the horse’s lungs), as well as any bacteria that are present.
In the lab, we use our cell-counting machine to determine the number of nucleated cells in the sample. These nucleated cells include cells from the surface of the trachea (epithelial cells) as well as macrophages and neutrophils, which are present at different stages of a bacterial infection. A high nucleated cell count is often suggestive of an active infection, especially if coupled with a high percentage of neutrophils on the resultant smear. This slide is made in a similar way to a blood smear, and is stained and read under the microscope. The percentages of each type of cell are noted, along with the presence of any blood or mucus, and this result is given to the vet who can then decide if treatment is necessary at this point.
We also culture tracheal washes on agar plates, which are then incubated for 24 hours. This encourages any bacteria present in the tracheal wash fluid to grow and allows our staff to identify them. If your horse has a relatively heavy bacterial growth, an antibiotic sensitivity will be carried out to allow the vet to prescribe the most effective antibiotic to get rid of the infection.