Necrotizing enterocolitis (damage and death of cells in small intestine and colon) is a serious disease of sudden onset in foals less than 4-6 days of age associated with a high death rate, despite therapeutic interventions. Clinical manifestations of enterocolitis in foals vary from being found dead to a spectrum of clinical manifestations.

The most common of these include failure to suckle or nurse, fever, depression, severe colic, and diarrhea. Although the association of Clostridium difficile, Neorickettsia risticii (which causes Potomac horse fever) and Salmonella infection with enterocolitis in adult horses is clearly established, many cases of fatal necrotizing enterocolitis in foals have no known risk factors.

Clostridium perfringens is the most commonly isolated clostridial species worldwide and is part of the normal intestinal flora. Following acquisition of this bacterium by the foal from the mare’s teats or the environment, the organism multiplies rapidly in the stomach and intestines. C. perfringens numbers are reduced fairly quickly, so that by the time foals are several months of age, the organism is found in relatively low numbers within the large intestine. The almost universal presence of C. perfringens type A in the intestine of healthy young animals has complicated the understanding of its role in enterocolitis. Although most strains don’t cause intestinal disease, there are two types that do so in foals.

One of these, C. perfringens type C, is a well-established but relatively uncommon cause of necrotizing enteritis. The other is C. perfringens type A, which includes a small subset that produces a novel pore-forming toxin called NetF (Necrotizing enteritis toxin, Foal). This novel toxin is related to the beta toxin of type C strains that causes severe enteric disease in foals, other species, and in humans. We found NetF-positive C. perfringens in 74% (11/15) of foals with necrotizing enteritis but not in 11 foals with undifferentiated diarrheal illness. In another study, NetF-positive C. perfringens was identified in 6 of 23 isolates from foals in Kentucky with severe enteritis. In adult horses with undifferentiated diarrhea, the detection rate of NetF among C. perfringens isolates was low (4/58). This would suggest this toxin is primarily associated with severe enteritis in neonatal foals