Page 728 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Respir atory system: 3.4 Medical conditions of the lower respir atory tr act 703

VetBooks.ir are no controlled studies evaluating this treatment Diagnosis
Clinical signs and history of seasonality are sug-
and efficacy is unknown.
Prognosis gestive. Radiography can be useful. An interstitial
pattern is present, with pulmonary over-inflation
Heaves is generally a life-long disease in affected in chronic cases (Fig. 3.163). Increased mucus is
horses, with progression in severity of signs and evident in the upper airways on bronchoscopy;
development of chronic airway remodelling occur- however, this is not diagnostic. BAL is a useful tool.
ring in animals with unregulated airway inflamma- Cytological examination of the fluid should be per-
tion. The prognosis for achieving and maintaining formed. An increased cell count with an increase in
remission from clinical signs is variable and is non-degenerative neutrophils is diagnostic.
highly dependent on the owner’s ability to institute
aggressive management changes that are successful Management
in reducing exposure to inhaled allergens all year Management factors are critical. Indoor housing in a
round. barn with minimal dust during the summer months
is important. Drug therapy as described for heaves
SUMMER PASTURE-ASSOCIATED is an important adjunctive measure (Table 3.4), but
OBSTRUCTIVE PULMONARY DISEASE response may be limited if environmental modifica-
tion is not feasible. Horses refractory to medical and
Definition/overview local environmental management may benefit from
This is a recurrent disease of adult horses that are relocation to a different climate.
kept on pasture. It is most common in the warm and
humid months of June to September in the south- Prognosis
eastern USA and in the UK. Animals gradually Although the prognosis for resolution of the disease
recover during the winter and spring months but is poor, careful environmental and medical man-
may experience a return of clinical signs the follow- agement may induce remission of clinical signs in
ing summer. affected animals.

Aetiology/pathophysiology
The pathophysiology of airway inflammation in this
condition is poorly understood, although it is pre- 3.163
sumed to represent an inflammatory response to
environmental allergens that are encountered at pas-
ture. Airway hyperresponsiveness has been linked
to increased bronchial smooth-muscle sensitivity to
5-hydroxytryptamine in affected horses.

Clinical presentation
The presentation is similar to heaves. Signs may
include nasal discharge, nostril flaring, coughing,
tachypnoea, laboured expiratory effort, expanded
lung field on chest percussion and crackles and
wheezes throughout the lung fields on thoracic
auscultation.
Fig. 3.163 Thoracic radiograph of a horse with
Differential diagnoses equine asthma. Findings include a diffuse interstitial
Heaves and viral or bacterial pneumonia are the pattern and mild concavity of the diaphragm due to
most common differential diagnoses. hyperinflation.