Congenital intestinal aganglionosis in white foals.

The research study examines a congenital neurological defect found in the intestines of foals born from overo horses. Symptoms of the defect include white hair, pink skin, and early onset colic, with a post-mortem examination revealing an absence of nerve cell clusters in the foals’ large and small intestines.

Objective and Methodology

• The research was conducted to study an apparent hereditary neurological defect in the intestines of foals, born from overo horses. The identified defect is thought to be congenital, meaning it is present at birth.
• These abnormalities were observed in six foals, all of which displayed the same physical characteristics and symptoms, including white hair, pink skin, and instances of colic within hours of birth.
• Post-mortem examination was conducted on the foals to uncover the anatomical root of the symptoms.

Findings

• The researchers found that all the foals showed physical attributes of a specific type of spotting pattern known as overo. This includes having white hair and pink skin, with occasional pigmented spots around the muzzle, ventral abdomen, and hindquarters.
• On the onset of symptoms, the foals appeared normal but soon showed signs of colic, a common digestive disorder in horses that can vary from mild to severe.
• Post-mortem examination revealed that the foals had a narrow and pale segment of large intestine. The issue was either confined to the small colon and rectum or involved the entire colon and rectum.
• Upon microscopic analysis, the research concluded that both myenteric and submucosal neuronal plexuses were absent in the large intestine and major parts of the small intestine. A neuronal plexus in these areas is crucial for control over intestinal muscle movement and fluid flow.
• The foals also showed an absence of melanin in the skin, which is the cause of their white hair and pink skin.

Implications

• This research helps in understanding that the spotting pattern, overo, might be associated with a congenital and hereditary neurological defect in foals. The association might allow breeders to perform genetic testing or prevent breeding of overo parent horses to avoid the occurrence of this fatal condition.
• The study also suggests that the observed phenotype of white hair and pink skin can potentially be used as an early identifier of this neurological defect.