What are the common causes of diarrhea in neonatal foals and how should each be treated?

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Foal diarrhea affects up to 80% of foals in the first 6 months of life and has both infectious and noninfectious causes that require distinct management approaches.14 More than 50% of foals experience one or more bouts of diarrhea before 6 months of age.3 The major infectious agents are equine rotavirus, equine coronavirus, Clostridioides difficile, Clostridium perfringens, Salmonella spp., Lawsonia intracellularis, Rhodococcus equi, Cryptosporidium spp., Strongyloides westeri, and Enterococcus durans.142 Noninfectious causes include overfeeding and improper nutrition such as feeding orphan foals calf milk replacer.11 --- Foal heat diarrhea is the most common noninfectious cause, occurring between days 5 and 15 of life coinciding with the dam's first postpartum estrus.1 Although most affected foals show no reduction in behavior, some suffer diarrhea for more than 20 days within the first 2 months and develop less well than foals with shorter diarrhea periods.1 Treatment is supportive; no pathogen-specific therapy is indicated. --- Rotavirus is the leading infectious cause of viral diarrhea in foals, and the infection itself is self-limiting.813 Treatment is supportive, including fluid and electrolyte support.8 Oral lactase administered every 4–6 hours aids small-intestinal digestion of lactose and reduces osmotic diarrhea.13 Prevention relies on vaccination of pregnant mares before parturition and ensuring adequate colostrum ingestion from vaccinated mares, combined with biosecurity measures.8 --- Equine coronavirus is an additional viral cause, though it is less prominent than rotavirus.1314 Treatment is supportive. --- Bacterial causes require pathogen-specific antimicrobial selection. Clostridium perfringens and Clostridioides difficile are frequently detected in hospitalized foals with diarrhea.2 Bacterial enterocolitis in neonatal foals can be a component of neonatal septicemia, and diarrhea can occur with bacteremia of any cause.4 Salmonella is also a recogniz