The conditions resulting in pain in the neonate overlap those conditions causing abdominal pain in the older foal; however, a few diseases are quite specific to the neonate. A brief description of these conditions in both the neonate and foal follows.
Table 1. Differential Diagnoses of the Foal with Abdominal Pain:
Meconium retention*
Enterocolitis
Herniation* (external and internal)
Uroperitoneum*
Small intestinal volvulus Ileus
Gastric outflow obstruction
Intussusception
Necrotizing enterocolitis
Focal infarction/necrosis
Large colon volvulus/displacement
Gastric ulceration
Peritonitis
Impaction (small bowel, large bowel,
small colon) Ovarian torsion
Fecalith
Intestinal atresia*
Ileocolonic aganglionosis*
*Indicates conditions that are more common in the neonate.
MECONIUM RETENTION- The initial passage of meconium usually begins in the first few hours after birth. Meconium passage is generally complete at 24 h of age, although it can take up to 48 h. Abdominal pain can be mild to severe. Retention may be high, in the transverse or right dorsal colon, or low, in the large colon. Contrast radiography through barium enema can be diagnostic:
ENTEROCOLITIS - Diarrhea has been reported to occur in 70 - 80% of foals, often during the first few weeks of life. Foal diarrhea is often of short duration and self-limiting. In severe cases, mortality can be high.
Causes of foal diarrhea are numerous; other than the `foal heat` diarrhea, infectious agents are the most common cause of enterocolitis. Generally, the abdominal pain is of mild degree and brief duration. Alternatively, acute enterocolitis can result in severe, progressive abdominal pain.
HERNIATION (External and Internal) - Herniation of abdominal contents can occur either externally (outside the body wall proper) or internally (through internal structures). Gastrointestinal herniation can result in abdominal pain as a result of either strangulating or non-strangulating obstructions. Herniation can be a result of acquired or congenital conditions. Inguinal and umbilical hernias are the more common external hernias, whereas diaphragmatic is the more common internal hernia.
Traumatic diaphragmatic hernias can be the result of blunt trauma, but are more frequently caused by laceration induced by fractured ribs. Other internal herniation includes rents in the gastrointestinal mesentery of small intestine, small colon, and the mesodiverticular band.
UROPERITONEUM - Ruptured bladder and urachus are the more common causes of uroperitoneum. Abdominal pain may ensue with progression of abdominal distention. In long standing cases, central nervous system signs such as uremic encephalopathy and deficits secondary to hyponatremia may be observed. Diagnosis can be based on typical electrolyte patterns in combination with peritoneal creatinine and abdominal ultrasound examination.
SMALL INTESTINAL VOLVULUS - Volvulus of the small intestine is one of the more common causes of the surgical abdomen in the foal. Presentation generally includes severe, progressive abdominal pain that is non-responsive to analgesics. When the strangulating lesions have been present for an extended period of time, these patients may present recumbent with abdominal pain and in varying degrees of cardiovascular collapse. Ultrasonographic evaluation identifies amotile loops of distended small intestine.
ILEUS - Ileus is defined as an absence of gastrointestinal motility with subsequent gastrointestinal distention. Possible causes may include electrolyte abnormalities, impaired autonomic nerve function, or inflammation caused by peritonitis or enteritis. Ileus can be particularly life threatening in the neonate or weak foal. Radiographs or abdominal ultrasound identify gas- or fluid-distended bowel.
GASTRIC OUTFLOW OBSTRUCTION- Gastric outflow obstruction can result from functional or mechanical disease. Mechanical obstruction is usually secondary to cicatrix formation subsequent to pyloric or duodenal ulceration. Functional obstruction is generally consequent to gastric or pyloric ulceration; the resultant inflammation interferes with coordinated gastric contraction and effective emptying of the stomach. Outflow obstruction of the stomach can be identified with contrast radiography performed by administering liquid barium through nasogastric tube. Surgical bypass, gastro-jejunostomy, and related procedures can be performed.
INTUSSUSCEPTION - Invagination of the small intestine into itself or into the cecum can result in edema, compromised vascular supply, and mild to severe abdominal pain. Suggested etiologies include parasitic infestation and alterations in motility secondary to enteritis. Abdominal ultrasound can be diagnostic: a target or bull`s eye sign is characteristic.
NECROTIZING ENTEROCOLITIS - Necrotizing enterocolitis is a condition resulting from hypoxemia or ischemia of the bowel wall. The disease is either diffusely or focally distributed throughout the gastrointestinal tract. The generalized condition is secondary to systematic hypoxemia and colonization of the bowel wall with micro-aerophilic gas forming bacteria or to bacterial invasion with pathogens such as clostridia.
Focal necrosing lesions can be caused by local bacterial invasion or by infarcts resulting from thromboembolism. Ultrasonographic evaluation may identify pneumatosis intestinalis (gas lucency in the wall of the bowel). Surgical resection of the affected areas may be beneficial.
LARGE COLON VOLVULUS - The strangulating lesions of the large colon are not as commonly identified in the foal as they are in the adult horse. Fermentation in the large bowel of the young foal has not reached adult capacity, and the foal is not as aggressively managed as the adult. Diagnosis is based on the degree and persistence of pain (identification of a surgical abdomen) and observations of large bowel distension through radiography or ultrasonography.
LARGE COLON DISPLACEMENT- As with large colon volvulus, displacement of the large colon is not a common cause of abdominal pain in the foal. The degree of pain in this condition is not as severe as for the strangulating lesion.
GASTRIC ULCERATION - Gastroduodenal ulceration can result in mild to severe abdominal pain in the foal. The classic clinical signs of ulcerative diseases are bruxism, ptyalism, and dorsal recumbency. The only accurate method of diagnosis is gastroscopy. Effective therapy includes proton pump inhibitors and anti-secretory drugs.
PERITONITIS - Inflammation of the peritoneal lining of the abdominal cavity can result in abdominal pain. Other clinical signs are dependent on the stage and severity of the disease.
In acute disease, signs of endotoxemic and/or hypovolemic shock typically overshadow signs of abdominal pain, whereas in chronic disease, signs of pain may be mild and intermittent. Diagnosis is based on centesis and analysis of peritoneal fluid. Ultrasonography may identify echogenic abdominal fluid.
SMALL INTESTINAL IMPACTION - Impactions of the small bowel with parasites, primarily ascarids, can occur, particularly subsequent to the use of efficacious anthelmintics in heavily infested foals. A parasite load can be visualized in the lumen of the small bowel using ultrasound. Gastric reflux may occasionally contain ascarids. Surgical correction of these impactions is usually required.
Source: W. V. Bernard (2003): Assessment of Abdominal Pain in Foals. In: Proceedings of the 49th Annual Convention of the American Association of Equine Practitioners, 2003, New Orleans, Louisiana (Ed.)
Publisher: American Association of Equine Practitioners, Lexington KY
Internet Publisher: International Veterinary Information Service, Ithaca NY (www.ivis.org), 2003; P0605.1103
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