Equine pleuropneumonia—a travel sickness

Transportation of horses over long distances is a common event in the Northern Territory and is the most common factor that predisposes horses to pleuropneumonia, also known as ‘travel sickness’, or ‘transport sickness.’

Horses normally breathe in small numbers of bacteria; healthy animals expel these bacteria rapidly. Respiratory tract disease develops when the number of bacteria entering the lung is greater than normal defence mechanisms can deal with, or the respiratory defences are not working properly.

Removal of bacteria needs to be rapid as the bacteria can multiply and the infection may spread from the airways in to the lung tissue. Infection of lung tissue, (pneumonia), is associated with general illness; the animal shows an increased temperature, loss of appetite and depression. Lung dysfunction causes an increased rate or depth of breathing, coughing and a rapid involvement of the chest wall lining. The horse may show pain and further respiratory distress due to accumulation of large amounts of fluid within the chest cavity. This is difficult to treat as many antibiotics are either inactivated by large amounts of accumulated pus, or do not penetrate lung tissue well.

Taking preventative measures is a far better option!

Note that these bacteria are not spread from one horse to another, that is, the disease is not contagious, but is caused by the horse’s own bacteria waiting for an opportunity to cause disease—so called ‘opportunistic pathogens’ which are found in all horses

Predisposing factors:

• head restraint—the single most important factor predisposing to pleuropneumonia associated with transport, is head restraint in an elevated position. It has been shown that this factor alone can lead to pleuropneumonia.

Severe contamination of the lower airways can occur after as few as six hours of head restraint in an elevated position. As a result, every effort must be made to restrain horses in a manner that enables them to lower their heads during and after transportation

Cross-tying at racetracks may also have the same adverse effect on the lower respiratory tract and would only exacerbate any adverse effects of long distant transportation that may have occurred

• dehydration—many horses will not eat adequate amounts of feed during a long distant trip and are even less likely to drink adequate amounts of water. In addition, allowing horses to eat during a journey with heads tied up could conceivably increase the risk of aspiration. An ‘average’ 450 kg horse in hot conditions may increase its consumption of water to 60 litres

• air pollutants—inadequate ventilation within transport vehicles, ammonia, and the inhalation of exhaust gases and road dust may also impair mucociliary clearance.

Recommendations to help prevent pleuropneumonia:

• minimise lower respiratory tract contamination—it has been shown that accumulated bacteria and secretions from within the airways was not removed when the horse’s head was periodically lowered by feeding or watering from the ground level for 30-minute periods each six hours. Therefore, for long distant transportation, breaking the journey up into 12 hour stages, the recommendation is that there are 8-12 hour breaks between stages
• feeding horses from ground level is preferable to feeding them from raised feeding containers
• avoid cross-tying or transporting horses for long periods immediately following exercise. A journey of as few as 2–4 hours, immediately after strenuous exercise, could cause problems
• prevent extension of bacterial infection from the airways into the lungs. This is unavoidable if horses have their heads elevated for more than 12 hours during transportation.

More information:

Leadon, D.P (1999) Equine Pleuropneumonia.