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.Journal of Vete… More than 50% of foals experience one or more bouts of diarrhea before 6 months of age.Veterinary Clin… 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.Journal of Vete…+1 Noninfectious causes include overfeeding and improper nutrition such as feeding orphan foals calf milk replacer.MSD Vet Manuals
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.BMC Veterinary… 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.BMC Veterinary… 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.Veterinary Clin…+1 Treatment is supportive, including fluid and electrolyte support.Veterinary Clin… Oral lactase administered every 4–6 hours aids small-intestinal digestion of lactose and reduces osmotic diarrhea.MSD Vet Manuals Prevention relies on vaccination of pregnant mares before parturition and ensuring adequate colostrum ingestion from vaccinated mares, combined with biosecurity measures.Veterinary Clin…
Equine coronavirus is an additional viral cause, though it is less prominent than rotavirus.MSD Vet Manuals+1 Treatment is supportive.
Bacterial causes require pathogen-specific antimicrobial selection. Clostridium perfringens and Clostridioides difficile are frequently detected in hospitalized foals with diarrhea.Journal of Vete… Bacterial enterocolitis in neonatal foals can be a component of neonatal septicemia, and diarrhea can occur with bacteremia of any cause.MSD Vet Manuals Salmonella is also a recognized cause in hospitalized foals.Journal of Vete…
For Lawsonia intracellularis (equine proliferative enteropathy, EPE), the clinical syndrome in weanling foals includes diarrhea, rapid weight loss, colic, lethargy, subcutaneous edema, and protein-losing enteropathy.MSD Vet Manuals A necrotizing form (N-EPE) presents with acute onset, rapid deterioration, and hemorrhagic diarrhea, and has been reported in foals as young as 5 weeks.Journal of the… Antimicrobials of choice for L. intracellularis are macrolides with or without rifampin, chloramphenicol, and tetracyclines — drugs not typically chosen as first-line therapy for a young foal with diarrhea.Journal of the… Macrolide-induced hyperthermia and tetracycline-induced nephrotoxicity are important adverse effects to anticipate, and macrolide use also carries risk of disrupting gastrointestinal flora in the dam if she is present.Journal of the… In N-EPE, broadening the antimicrobial spectrum to address secondary bacterial colonization, endotoxemia, and disseminated intravascular coagulopathy is warranted.Journal of the…
For Enterococcus durans, detection is strongly associated with diarrhea in neonatal foals; 71% of foals with diarrhea tested positive for E. durans compared with 0% of foals without diarrhea.Journal of Vete… Transmission occurs both from broodmares and laterally between foals, making enhanced biosecurity measures essential to mitigate spread.Journal of Vete… Specific antimicrobial dosing for E. durans in foals is not described in the veterinary literature.
Infectious causes should always be identified to guide therapy, prevent outbreaks, and assess zoonotic risk.Veterinary Clin… It is critical to differentiate foals manageable in field conditions from those requiring referral, based on the degree of systemic compromise.Veterinary Clin… Foals with diarrhea commonly develop enteritis associated with systemic inflammatory response syndrome, and treatment is primarily symptomatic with pathogen-specific therapy added when an agent is identified.Veterinary Clin…
| Cause | Category | Key Clinical Features | Treatment | Key Caveat |
|---|---|---|---|---|
| Foal heat diarrhea | Noninfectious | Days 5–15 of life, mild | Supportive | No pathogen; most foals unaffected behaviorally BMC Veterinary… |
| Rotavirus | Viral | Self-limiting; most common infectious cause | Supportive; oral lactase q4–6h MSD Vet Manuals | Prevent via mare vaccination + colostrum Veterinary Clin… |
| Coronavirus | Viral | Less common than rotavirus | Supportive | MSD Vet Manuals+1 |
| C. perfringens / C. difficile | Bacterial | Common in hospitalized foals | Pathogen-specific antimicrobials | Can be component of neonatal septicemia Journal of Vete…+1 |
| Salmonella | Bacterial | Hospitalized foals; hemorrhagic diarrhea | Pathogen-specific antimicrobials; biosecurity | Zoonotic risk Journal of Vete…+1 |
| L. intracellularis (EPE/N-EPE) | Bacterial | Weanlings; weight loss, edema, protein-losing enteropathy; N-EPE: acute hemorrhagic, rapid death | Macrolides ± rifampin, chloramphenicol, or tetracyclines Journal of the… | Macrolide hyperthermia; tetracycline nephrotoxicity; N-EPE reported as young as 5 weeks Journal of the… |
| E. durans | Bacterial | Neonatal; lateral + dam transmission | Enhanced biosecurity; specific dosing not established Journal of Vete… | 71% of diarrheic foals positive vs. 0% of healthy foals Journal of Vete… |
| Cryptosporidium / Strongyloides westeri | Protozoal/Parasitic | Variable age | Pathogen-specific where available | Journal of Vete… |
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