Summer Pasture-Associated Recurrent Airway Obstruction
(SPA-RAO)
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This article is still under construction. |
Also known as: Summer Pasture-Associated Obstructive Pulmonary Disease, Summer Pasture-Associated Heaves
Description
Summer Pasture-Associated Recurrent Airway Obstruction(SPA-RAO) is an inflammatory condition of the lower airways affecting pasture-kept horses. This is in contrast to Recurrent Airway Obstruction that affects horses that are stabled and fed hay. The disease is characterised by airway inflammation, increased airway mucus production, reduced mucociliary clearance and bronchoconstriction. The disease occurs most commonly in the South of the United States.
Signalment
The average age of onset of SPA-RAO is 9 years of age. There is no reported sex predilection but Quarter Horses are overrepresented.
Pathogenesis
The pathogenesis of the disease is largely unknown but suggested hypotheses include inhaled pollens or outdoor moulds or ingestion of a pasture-derived pneumotoxin.
Clinical signs
Clinical signs are similar to those associated with RAO but occur in horses kept out at pasture during the summer months, usually for more than twelve hours a day. Signs may include exercise intolerance, cough (often productive), dyspnoea, increased expiratory effort and flared nostrils. Pyrexia is not usually a feature of SPA-RAO. In severe cases, affected horses stand with their neck arched and elbows abducted. An abdominal 'heave' line may also be visible due to hypertrophy of the external abdominal oblique muscles. Lung field auscultation reveals fine crackles and wheezes. In severe cases, wheezes may be audible without a stethoscope.
Diagnosis
Diagnosis is usually pased on the characteristic clinical signs combined with a history of seasonal occurrence and exposure to pasture during late spring or summer. If hay appears to act as a trigger to the horse, a complete pelleted diet may be fed or alternatively hay should be soaked. Alfalfa has been previously associated with less respiratory problems than grass hay and may be preferable.
Treatment and management
Affected horses should only be allowed access to pasture during late autumn, winter and early spring.
References
- McGorum, B. C., Edward Robinson, N., Dixon, P. M., Schumacher, J. (2007) Equine respiratory medicine and surgery Elsevier Health Sciences
- Orsini, J. A., Divers, T. (2007) Equine Emergencies: Treatment and Procedures Elsevier Health Sciences