Dysphagia in the neonatal foal manifests itself as the presence of milk in the foal's nares after nursing. Milk reflux in
a foal should not be ignored. Aspiration pneumonia is the usual secondary consequence.
Foals with mild dysphagia can appear normal at birth except for the presence of milk at the nose. As aspiration pneumonia
develops, wheezes and crackles may be heard on auscultation of the lungs. A rattle in the trachea from the aspirated milk
often can be felt after the foal suckles. If obstruction of the upper airways occurs as part of the dysphagia, stridor, heightened
upper respiratory noise and increased inspiratory effort can be prominent clinical signs (Table 1).
Table 1: Causes of upper airway dysfunction in foals categorized by presenting sign of stridor
Differential diagnosis for dysphagia
The differential diagnoses for dysphagia in the foal are many and can include: dorsal displacement of the soft palate, rostral
displacement of the palatopharyngeal arch, cleft palate, subepiglottic and pharyngeal cysts, bilateral laryngeal paralysis
and arytenoid chondritis.
In a study of 38 foals with milk regurgitation/upper airway problems, 34 percent presented with dorsal displacement of the
soft palate (DDSP). DDSP can be seen alone or in conjunction with rostral displacement of palatopharyngeal arch, redundancy
of the soft palate or a persistent epiglottal frenulum. Prematurity, perinatal asphyxia and white muscle disease (nutritional
myodegeneration, NMD) can be risk factors for the development of DDSP. In a review of 29 cases of NMD in foals, 52 percent
of the foals presented with dysphagia as one of the clinical signs. Cerebral or brain stem disease may also influence the
ability to swallow.
Unlike in humans where orofacial clefts, congenital fissures in the median line of the palate, are a common birth defect,
cleft palate in the foal is very rare. The heritability of the cleft palate in the horse is unknown. The milk regurgitation
is noted during the first nursing bout.
Subepiglottic and dorsal pharyngeal cysts also can interfere with the swallowing mechanism in the foal and cause upper-airway
obstruction. These cysts are thought to originate from the thyroglossal and craniopharyngeal ducts, respectively.
Bilateral laryngeal paralysis and arytenoid chondritis have also been recognized in the newborn foal. Clinically these foals
presented with respiratory distress. Laryngeal paralysis has been associated with cerebral diseases, such as congenital hydrocephalus.
Arytenoid chondritis appears as an enlargement of the arytenoid cartilage and may mimic laryngeal paralysis.
Upper-airway endoscopy is the most rewarding diagnostic test for finding the origin of the milk regurgitation. It is best
performed with manual restraint of the foal because sedation might affect the findings. A 1-meter, 1-1.5 cm diameter endoscope
can be passed easily in a foal less than 40 kg. Milk in the trachea is evidence that aspiration is occurring.
Figure 1: Endoscopic view of a foal with DDSP. Note the displacement of the soft palate over the epiglottis and the mild rostral
displacement of the palatopharyngeal arch (Equine Neonatal Medicine: A Case Based Approach, Spring 2006, Elsevier).