MSD Manual

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Professional Version

Parasitism (Gastrointestinal) in Horses


Allison J. Stewart

, BVSC (Hons), MS, DACVIM-LA, DACVECC, The University of Queensland

Last full review/revision Sep 2013 | Content last modified Jun 2016

Both large and small strongyles have been incriminated as a cause of chronic diarrhea in horses and foals. The condition associated with small strongyles in horses is termed cyathomostomiasis and has been reported to result in recurrent colic, diarrhea, and weight loss. ( See Gastrointestinal Parasites of Horses Gastrointestinal Parasites of Horses .)

Giardiasis ( see Giardiasis (Giardia) Giardiasis (Giardia) ) has been reported in a limited number of cases as a cause of intermittent diarrhea in horses. However, Giardia can also be found in the feces of a small number of healthy horses and is rarely recognized as a cause of diarrhea in horses. Cryptosporidia ( see Cryptosporidiosis Cryptosporidiosis ) have been identified in the feces of both healthy and diarrheic foals. There is evidence that Cryptosporidium spp can cause diarrhea and even death in immunocompetent foals; cryptosporidia have been described as a cause of outbreaks of foal diarrhea on some farms.

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