The equine respiritory system
There are a number of respiratory diseases and airway conditions that affect horses.
Respiratory disease is responsible for over 20% of all lost training days. Only lameness causes a greater number of last training days, compared with respiratory disease.
The respiratory system of the horse is well adapted to athletic exercise, with unrestricted upper airway diameters, and a large lung capacity afforded by 18 ribs. These combine to enable air intakes of up to 1800 litres per minute in a galloping horse. Volumes of up to 300 litres of blood are pumped at high pressure through small lung capillaries surrounding 10 million air sacs to take up and deliver over 70 litres of oxygen per minute to the working muscles at the gallop.
As a result, any restriction in upper airway diameter, obstruction of the airways, diseases or stress related conditions that reduce efficiency of oxygen uptake from the air sacs, can have a great influence on athletic capacity.
The large lung surface and high blood flow rates also provide the additional function of heat loss during and after exercise, with up to 20% of the muscle heat generated during exercise being exchanged across the lung surface to supplement sweating and other skin surface heat loss mechanisms.
The respiratory system is continually challenged by a large amount of foreign material, including viruses, bacteria and fungi inhaled in air from the arena surfaces during exercise, or from dusty bedding, feed and stable environments.
Horses can be susceptible to a number of conditions that affect the respiratory tract. Some of the most common invaders or ailments include viral Infections such as Equine Influenza and Equine Herpes Virus, parasitic infections such as the lung worm Dictyocaulus arnfieldi, allergies like COPD and exercise induced ailments pulmonary haemorrhage EIPH.
If the horse is coughing during exercise, when eating or at rest he may have a respiratory infection . If the condition is infectious your horse may have a temperature (normal 99.5-100.5F) and may appear depressed. Nasal discharge may be present; it may be clear initially, later becoming white and purulent. Other symptoms include an increased respiratory rate, wheeziness, exercise intolerance and depressed appetite.
What to do if you suspect your horse is affected
If an infectious cause is suspected isolate your horse from other horses, as it may be contagious. Phone your vet. Do not exercise your horse until it has been examined. If an allergy is suspected discuss the environmental changes that may be necessary with your vet. Only use the best quality bedding materials, preferably shavings or shredded paper. Feed the best quality hay available, soak over night with water. Or use a hay alternative such as haylage. Ensure the stable ventilation is adequate. Keep the stable very clean, paying particular attention to the walls and feed bowl. Remove any uneaten feed from the feed bowl as amounts left may grow moulds. If the allergy problem persists, samples and swabs may be taken from your horses' environment to identify the specific agent your horse may be allergic to.
Ensure good stable management. Vaccination is available for equine influenza, and is recommended under most circumstances. Implement a regular and effective worming program. Remember if you have donkeys in the same field as your horse they can carry lungworm and show no signs. If new horses are coming into the yard, isolate them if possible for the first ten days as they may be incubating a respiratory disease. The use of supplements can also help to assist the horse in breathing, paricularly in dusty environments.