Page 696 - The Veterinary Care of the Horse

Causes

The cause is thought to be a hypersensitivity of the lungs to inhaled pollens and moulds. The
VetBooks.ir symptoms are often worse when conditions are hot and dusty. Once the airways become

hyper-responsive, non-specific triggers such as cold or dry air, irritant dust and exercise may
exacerbate the condition. Harvesting of crops in nearby fields is a common trigger.

Clinical signs

These include:

• severe respiratory distress with fast, shallow breathing
• breathing out is particularly laboured as the airways are obstructed

• there is a marked abdominal lift on expiration as the muscles are used to help force air

out of the lungs
• a ‘heave line’ develops in the muscles on each side of the ventral abdomen

• coughing

• flared nostrils

• nasal discharge
• anal movements in time with respiration due to extra abdominal effort

• crackling and wheezing sounds if the condition is severe.

Mildly affected horses and ponies have a normal appetite and demeanour. In a severe case the
animal will have a bluish tinge to the mucous membranes due to receiving insufficient
oxygen. If the condition is chronic and severe, the affected animal is likely to experience

some weight loss. If left untreated, SPAOPD can be life-threatening.

WHY DOES THE HORSE DEVELOP THESE SIGNS?

As with RAO, the respiratory tract is hyper-responsive to inhaled allergens. The end result is

inflammation and swelling of the airway walls, excessive production of mucus and
bronchospasm, all of which cause narrowing of the airways.

Diagnosis

Diagnosis is made on the history and the clinical signs. If bronchial secretions are examined
under the microscope they have an abnormally high percentage of neutrophils.