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Foal diarrhea: causes, diagnosis and treatment (Proceedings)

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Aug 01, 2011

Diarrhea is a significant cause of morbidity and mortality in foals. Numerous noninfectious and infectious agents are responsible for enterocolitis and enteritis in the newborn foal. Altered fecal consistency may be associated with uncomplicated diarrhea which often does not require treatment, to life threatening enteritis or enterocolitis with endotoxemia and clinical signs associated with systemic inflammation. Associated metabolic complications include acidosis, hypovolemic shock, hypotension, and bacteremia. Therapy is dependent on the severity, suspected etiology and concomitant complications. Supportive care and rehydration to prevent hypovolemic shock and renal damage can be life threatening. Antibiotic therapy is only required if bacterial enteritis is suspected or if there is the possibility for bacterial translocation across the compromised gastrointestinal tract.

"Foal heat" diarrhea

Mild diarrhea without signs of systemic disease or inflammation is commonly observed in foals between 5 and 15 days of age. Foals remain bright and alert, continue to nurse and no abnormalities are present on hematology and biochemistry results. The term "foal heat" is a misnomer, as diarrhea also occurs in orphan foals raised on milk replacement formulas.

Although not proven, it is postulated that maturational changes of the gastrointestinal (GI) tract associated with initiation of feed ingestion and inoculation of microflora by coprophagy resulting in the establishment of normal GI flora, are responsible for the altered fecal consistency. Foals should be monitored closely for any signs of systemic disease, including depression, dehydration, fever or reduced appetite, as early enteritis can mimic foal heat diarrhea. No treatment is required for foal heat diarrhea, however cleaning the perineum and topical application of Vaseline, or a Zinc Oxide preparation can help prevent scalding.

Mechanical irritation by sand or foreign material

Ingestion of sand, dirt, shavings, rice or almond hulls can cause mechanical irritation to the GI tract and subsequent diarrhea. Colic and abdominal distention are commonly present with these forms of diarrhea. Diagnosis is easily made evaluation of the feces. Abdominal radiography can be used to definitively diagnose radio-dense material such as sand, and with practice ultrasonography can also be used.

Treatment of foals with sand accumulation includes supportive care with intravenous fluid therapy and enteral laxatives, including mineral oil and psyllium. Occasionally, foals with sand impactions require surgical evacuation.

Hypoxic gastrointestinal damage

Peripartum asphyxia syndrome, also referred to as hypoxic-ischemic encephalopathy or "Dummy foal syndrome" can result in ischemic damage to the GI tract, kidneys, heart and brain. Any cause of poor oxygen delivery in the peripartum period resulting from dystocia, cesarean section, umbilical cord problems, or abnormal oxygenation in the immediate postpartum period can result in hypoxic gut injury secondary to hypoperfusion, ischemia-reperfusion injury, and inflammatory mediators. Clinical signs associated with ischemic gastro or enterocolitis include gastroduodenal reflux, ileus, intolerance to enteral feeding, colic, abdominal distention, and diarrhea.

These foals often require intensive care due to renal, cerebral and cardiac dysfunction. Foals with asphyxia-associated diarrhea should be monitored for nasogastric reflux, bloating (bloat-tape) and gastrointestinal distension and motility by ultrasonographic examination. They should be fed very conservatively through the enteral route (initially only 3-5 % of their body weight in mare's milk divided into hourly feedings: ie ~ 100mls/hr). For the initial 24 hours, nutrition can be supplemented by the addition of 5-10% dextrose to balanced electrolyte solutions administered at 60-120 mls/kg/hr, depending on the degree of dehydration and on-going gastrointestinal losses. Parenteral nutrition, with only small volumes of enteral milk to provide local nutrients to enterocytes is beneficial in severely affected foals. Partial gastrointestinal rest can prevent reflux, bloating and diarrhea. These neonates are at high risk of developing sepsis, and broad-spectrum systemic antimicrobial therapy is recommended.

Nutritional causes of diarrhea

Foals fed with milk replacer develop loose feces more frequently often than those fed mare's or goat's milk, especially if erroneously made either too concentrated or too dilute.

Lactose intolerance

Lactase is made by the cells in the tips of the small intestinal mucosal brush border. Primary lactase deficiency is rare in foals, but lactase deficiency secondary to damaged intestinal villi tip cells by infectious agents such as rotavirus and Clostridium difficile is not uncommon.

Supplementation with a lactase is indicated in foals with suspected lactase deficiency. Although lactose intolerance can be confirmed with a lactose tolerance test, as supplementation is inexpensive, practical and safe, testing is not usually performed.