Todayโs path rounds are on ๐ซ๐๐๐ฎ๐ซ๐ซ๐๐ง๐ญ ๐๐ข๐ซ๐ฐ๐๐ฒ ๐จ๐๐ฌ๐ญ๐ซ๐ฎ๐๐ญ๐ข๐จ๐ง, otherwise known as heaves!
๐๐ก๐๐ญ ๐ข๐ฌ ๐ข๐ญ?
๐๐๐๐ฎ๐ซ๐ซ๐๐ง๐ญ ๐๐ข๐ซ๐ฐ๐๐ฒ ๐จ๐๐ฌ๐ญ๐ซ๐ฎ๐๐ญ๐ข๐จ๐ง is a condition of the lungs in horses, which is similar to human asthma. In this disease, the airways are sensitive to allergens, causing them to constrict and prevent airflow through the lung. In chronic cases, the airways may also become obstructed by overproduction of mucus, or thickening of the airway walls.
๐๐ก๐จ ๐ ๐๐ญ๐ฌ ๐ข๐ญ?
As mentioned previously, this is a disease seen in horses, typically mature horses. These horses typically have an โallergyโ or sensitivity to mold spores or hay dust, which triggers airway obstruction.
๐๐ก๐ฒ ๐ข๐ฌ ๐ญ๐ก๐ข๐ฌ ๐ ๐ฉ๐ซ๐จ๐๐ฅ๐๐ฆ?
At the microscopic level, the ๐๐ซ๐จ๐ง๐๐ก๐ข๐จ๐ฅ๐๐ฌ, the small airways of the lung, often contain mucus and inflammatory cells that are reacting to the allergen. Around the bronchioles, the muscle that controls their diameter is ๐ก๐ฒ๐ฉ๐๐ซ๐ญ๐ซ๐จ๐ฉ๐ก๐ข๐๐ (thicker), because every time the allergen is encountered, they contract. Ultimately, both of these factors prevents adequate airflow through the lungs.
Due to inadequate airflow, horses often present with ๐ข๐ง๐๐ซ๐๐๐ฌ๐๐ ๐ซ๐๐ฌ๐ฉ๐ข๐ซ๐๐ญ๐จ๐ซ๐ฒ ๐๐๐๐จ๐ซ๐ญ, because they are trying desperately to get as much airflow in and out of their closed off lungs as they can. Horses will often wheeze, be unwilling to exercise, and may develop a cough or nasal discharge. These clinical signs can be seasonal, depending on dust exposure.
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐๐ข๐๐ ๐ง๐จ๐ฌ๐๐?
Heaves is typically diagnosed based on the clinical signs and history of the animal. A classic โsignโ of heaves is a ๐ก๐๐๐ฏ๐ ๐ฅ๐ข๐ง๐, where the abdomen has a deeply indented line caused by increased abdominal muscle use as the horse tries to breathe. If a veterinarian wants to confirm the diagnosis, they can do a ๐๐ซ๐จ๐ง๐๐ก๐จ๐๐ฅ๐ฏ๐๐จ๐ฅ๐๐ซ ๐ฅ๐๐ฏ๐๐ ๐, which is where they introduce sterile saline into the lungs and then retrieve it. The saline that comes back will contain inflammatory cells from the lungs that can then be used to diagnose the disease. Neat!
At necropsy, there arenโt too many interesting findings. Sometimes, the mucus accumulations in the small airways can be seen as small, grey dots throughout the lungs. In chronic, very severe cases, we may see thickening of the ๐๐ข๐๐ฉ๐ก๐ซ๐๐ ๐ฆ, the muscle that allows for your lungs to inflate, because it is having to work extra hard to allow breathing. We may also see ๐ฉ๐๐ฌ๐ฌ๐ข๐ฏ๐ ๐๐จ๐ง๐ ๐๐ฌ๐ญ๐ข๐จ๐ง (low blood flow) in the liver, because of downstream effects that improper airflow through the lungs can cause for the heart.
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐ญ๐ซ๐๐๐ญ๐๐?
The most important treatment is to reduce allergen exposure. Horses should be kept outdoors as much as possible, and eat soaked hay or hay cubes to reduce dust. Sometimes medications like ๐๐ซ๐จ๐ง๐๐ก๐จ๐๐ข๐ฅ๐๐ญ๐ข๐ง๐ ๐๐ ๐๐ง๐ญ๐ฌ (expand the small airways) are used to counteract the constriction in response to allergens. ๐๐จ๐ซ๐ญ๐ข๐๐จ๐ฌ๐ญ๐๐ซ๐จ๐ข๐๐ฌ (anti-inflammatory medications) can also be used to reduce the inflammation within the airways.
๐๐ก๐จ๐ญ๐จ๐ฌ
1) A horse with a โheave lineโ.
2) Little grey spots throughout the lungs due to mucus accumulation.
3) Thickening of the diaphragm due to heaves.
4) Passive congestion of the liver due to heaves.
5) Mucus and inflammatory cells in the airway due to heaves.
๐๐จ๐ฎ๐ซ๐๐๐ฌ
Maxie, G. Jubb, Kennedy and Palmerโs Pathology of Domestic Animals, Volume 2. Sixth Edition.
Rush, B.R. Recurrent Airway Obstruction in Horses. Merck Veterinary Manual 2014.
Photo 1 courtesy of Deben Valley Vet.
Photos 2-5 courtesy of Noahโs Arkive.
