Page 638 - The Veterinary Care of the Horse

• Cytology The sample is examined under a microscope. It will contain epithelial cells,

macrophages, neutrophils, lymphocytes, eosinophils and possibly red blood cells. The
VetBooks.ir numbers of these are compared with those from the tracheal secretions of a normal horse.
The degree of inflammation can be assessed and graded. A high number of eosinophils

may be indicative of parasitic infection. Lungworm larvae can sometimes be seen in the
washes from infected horses.

• Bacteriology The wash may contain large numbers of pathogenic bacteria. These are

cultured in the laboratory and their sensitivity to different antibiotics is tested. This helps
the vet choose the correct antibiotic to eliminate the bacteria.

Bronchoalveolar lavage (BAL)

Bronchoalveolar lavage (BAL) is used to investigate diseases of the lower respiratory tract.
The advantage over tracheal washes is that cells from the lower airways are aspirated and

these tend to reflect more accurately the disease processes in the alveoli (air sacs) and small
airways. The technique is particularly valuable in the diagnosis of:

• small airway inflammatory disease
• recurrent airway obstruction

• summer pasture associated obstructive disease

• the diagnosis of pneumonia caused by bacteria.

PROCEDURE

The technique may be performed through a long endoscope and catheter or by insertion of a
special BAL tube into the small airways via the nostril. It is essential that the horse stays still

for this procedure, so sedation and a twitch are routinely used. A bronchodilator may be
administered to reduce coughing or more commonly local anaesthetic is instilled into the

airways before the endoscope or tube is passed to minimize coughing.
The endoscope or BAL tube is inserted until resistance is encountered. Once the BAL

tube has lodged in a small airway, an inflatable cuff just behind the tip is blown up with air to
secure it in position and prevent the escape of fluid. If an endoscope is used, a catheter is now

passed along the biopsy channel. Between 150–250 ml of warmed sterile saline is instilled
into the airway and immediately aspirated. All of the equipment used is sterile.

The aspirated samples are centrifuged and the cells obtained are smeared onto a slide and
examined under the microscope. Cultures can also be performed if infection is suspected.

Following the procedure, the horse should not be allowed to eat until the effects of the
sedation and local anaesthesia have worn off, to ensure that it can swallow safely.