Initial treatment and determining the underlying cause
One way to stop the aspiration of milk is to temporarily muzzle the foal, place an indwelling stomach tube and feed the foal
this way for a few days while re-evaluating its condition. "If it does regain its ability to swallow, then it's on its way
and can do well," Palmer says. "If it doesn't and continues to aspirate, then I've been most successful managing this by weaning
the foal from the mare and feeding it from a bucket on the ground. As long as its head is below its lungs so that the fluid
drains out its nose instead of down its trachea, it does all right." Once affected foals are able to eat solid food, the problem
Photo 3: A lateral skull radiograph with the soft palate displaced above the epiglottis. (PHOTOS: COURTESY OF DR. MARY ROSE
Determining the cause of the dysfunction is essential to guiding treatment. "There are two diagnostic tests that I find important
— upper airway endoscopy and radiography," says Paradis. Endoscopy of the upper airway allows you to observe the function
of the larynx and soft palate. Radiographic evaluation should include a lateral radiograph of the head, looking at the epiglottis
in relationship to the soft palate to tell whether it's displaced (Photo 3), as well as radiographs of the chest to determine
the extent of the aspiration pneumonia. Aspiration pneumonia tends to produce a distinctive radiographic pattern in the caudal
ventral lung lobe (Photo 4).
Photo 4: A lateral radiograph of a foal with aspiration pneumonia. Note the bronchoalveolar pattern in the caudal ventral
lung field. (PHOTOS: COURTESY OF DR. MARY ROSE PARADIS)
Most foals with dysphagia have a weakness in their soft palate causing dorsal displacement of the soft palate (DDSP) and sometimes
a collapse of the pharyngeal walls. DDSP in foals may be due to prematurity or muscular weakness due to vitamin E or selenium
deficiency, or it may be idiopathic. In severe cases, the foal will have difficulty breathing. In this situation, "it may
be difficult to visualize the larynx due to the collapse of the pharyngeal walls. It is almost as if they're breathing through
a space the size of a straw," Paradis says.
Since both dysphagia and aspiration pneumonia may be accompanied by increased respiratory effort, it is necessary to diagnose
the cause. Endoscopic evaluation will help determine whether the respiratory difficulty is due to laryngeal or pharyngeal
conditions such as DDSP and collapse of the pharynx or not.
Other conditions resulting in dysphagia and milk aspiration include pharyngeal or laryngeal cysts, laryngeal paralysis and
arytenoiditis. A cyst can develop off the dorsal pharyngeal wall or underneath the soft palate. This causes a break in the
seal of the larynx when the foal nurses. "Foals with laryngeal paralysis or arytenoiditis generally present in respiratory
distress and often need an emergency tracheotomy," Paradis says.
Lastly, another differential diagnosis to consider is a congenital esophageal stricture. "This will prevent them from clearing
their esophagus of milk," Palmer says. This is an uncommon cause of dysphagia that carries a poor prognosis.
The treatment and prognosis for milk aspiration depend on the cause. "The first step in treatment is to muzzle the foal and
begin feeding through an indwelling stomach tube," says Paradis. "Next, broad-spectrum antibiotics are important to treat
the pneumonia. For cases of DDSP, it is necessary to determine the cause. For example, if the DDSP is secondary to a vitamin
E and selenium deficiency — also known as white muscle disease — and is confirmed by detection of elevated serum creatine kinase (CK) activity, you would treat with vitamin E and selenium.
If you think the muscle weakness is due to prematurity, you should tube feed for a number of days, rechecking endoscopically
or radiographically to see if there is resolution as the foal matures."
If a pharyngeal cyst is the cause of the dysphagia, then it needs to be removed. This can be accomplished easily with a laser.
Be sure to continue to tube feed the foal until it heals. If laryngeal paralysis or arytenoiditis is the problem, the prognosis
is poor. "You then need to be thinking about surgical intervention such as a tie-back surgery or arytenoidectomy with the
knowledge that you may be creating a problem that can worsen the aspiration," says Paradis.
Most foals with aspiration pneumonia do well with proper treatment. "It's surprising how well neonatal foals recover from
pulmonary disease." Palmer adds.
Ed Kane, PhD, is a researcher and consultant in animal nutrition. He is an author and editor on nutrition, physiology and veterinary medicine
with a background in horses, pets and livestock. He is based in Seattle.