Answers Sought in Treating Foal Respiratory Disease

By Andrea Lin

If you weighed a thousand pounds or more and had lung disease, your doctor would have a hard time getting a look at the problem. That's because imaging techniques have size limitations: radiographs (X rays) are limited by the beam penetration as well as by the types of views possible with large animals; ultrasound waves also can penetrate only to a certain depth; computed tomography (CT) and magnetic resonance imaging (MRI) are limited by the size of the gantry (frame) and the weight-limit of the table.

Such is the fate of horses: many imaging modalities cannot accommodate their large size.

Luckily, however, foals with lung disease are small enough to fit comfortably within the gantry of a CT machine. Foals up to 2 weeks old weigh between 100 and 160 pounds, which is easily supported by the table.

Kara Lascola, DVM, Dipl. ACVIM, an equine veterinarian at the University of Illinois Veterinary Teaching Hospital in Urbana, treats very young foals that have respiratory disease, a potentially life-threatening illness. Some respiratory problems, for example, pneumonia, originate in the lungs, while others are secondary to an infection originating elsewhere in the body. In either case, the treatment and prognosis for the foal depend on how severe the disease is and where in the lungs it is.

"Currently the main tools veterinarians use to assess foal respiratory disease are radiographs, ultrasound, blood values, and clinical signs," says Lascola. "Unfortunately, radiographs may lack sensitivity for revealing the extent of respiratory disease. In human medicine, CT has been proven more sensitive than radiographs for imaging lung disease."

To see if this holds true for foals as well, Lascola is conducting research on the value of CT imaging for diagnosing respiratory disease in young foals. Her first step is collecting data on CT imaging of healthy foals.

Although CT works well in people with lung disease, foals are definitely not the same as people. They are similar in weight to human adults, but their body mass and shape are quite different. In foals the lower areas of the lungs are compressed by gravity and by the animal's weight. These varying areas of density can be seen on a CT scan, but until now there had been no data to define what is normal and what indicates disease on a CT image of foals' lungs.

In addition to improved sensitivity, CT scans also offer greater speed. It takes only five minutes to position and scan a foal using the spiral CT machine at the University of Illinois veterinary hospital. Although longer procedures may require use of intravenous sedation to keep the patient still, in many cases a sick foal won't need any sedation to be scanned. Because sedation poses certain risks, especially in sick patients, a speedy, sedation-free CT scan is safer and causes less stress on the foal.

"Not only will CT imaging be useful for initial diagnosis of lung disease," says Lascola, "but follow-up imaging will enable veterinarians to determine whether the treatment is effective so we can alter the treatment plan, if needed."

Lascola's findings will help set standards for use of CT imaging in foals with respiratory disease so that this new imaging tool can improve diagnosis and treatment.

For more information about horse health, please contact your local equine veterinarian.

Reprinted with permission of the University of Illinois College of Veterinary Medicine Veterinary Extension/Office of Public Engagement.

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University of Illinois College of Veterinary Medicine

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