Diarrhea: What the Research Says
Evidence from 28 peer-reviewed studies
1 Systematic Review
11 Cohort Study
11 Case Report
5 Expert Opinion
What Professionals Should Know
- •Do not routinely recommend probiotic supplements to improve digestive efficiency or prevent common gastrointestinal conditions like colic or salmonellosis in horses
- •Exercise caution with high-dose novel probiotic products, as they may worsen diarrhea rather than improve it
- •Consider multistrain probiotic formulations for performance horses where improved stamina and aerobic fitness are goals, though evidence remains limited
- •Camels and donkeys in the Nigeria-Sahel region should be considered potential reservoirs for Schmallenberg virus; monitor these species during livestock trading and migration to prevent transboundary spread to domestic ruminant herds
- •Older animals show higher infection rates; prioritize surveillance and biosecurity measures for older camels and donkeys, particularly in high-risk geographic areas
- •Geographic hotspots exist for SBV exposure; implement targeted disease monitoring and movement restrictions in identified clustering areas (Zangon Daura for camels, Sule Tankarkar for donkeys) to reduce regional transmission risk
- •Rabbits can harbor and shed L. intracellularis; consider them a potential disease reservoir when managing multi-species farms with horses or pigs
- •Diarrhea outbreaks in rabbit populations warrant investigation for L. intracellularis as a potential zoonotic or cross-species transmission risk
- •Biosecurity protocols on farms with both rabbits and horses/pigs should account for L. intracellularis as a cross-species pathogen
- •Diarrhea in horses involves fundamental disruption of gut bacterial communities, suggesting microbiota-targeted interventions (probiotics, prebiotics, dietary management) may have therapeutic potential beyond treating secondary causes.
- •Monitoring or manipulating specific bacterial populations could become part of future diarrhea prevention and treatment protocols in equine practice.
- •Horses recovering from diarrhea may require extended management to restore normal microbial diversity and function, not just resolution of clinical signs.
- •Gut fungal dysbiosis is a significant marker of diarrhea in horses; monitoring fungal community composition may help identify disease states early
- •The dramatic reduction and loss of fungal diversity during diarrhea suggests that restoring fungal community diversity could be a therapeutic target for managing equine diarrhea
- •Understanding the specific fungi that disappear during diarrhea may lead to targeted probiotic or prebiotic interventions to prevent or treat the condition
- •Ensure unbroken horses receive proper fitness-for-transport assessment before long journeys; the low injury/disease rates here reflect good baseline selection and handling by experienced staff
- •Maintain adequate temperature control, space allowance (loose housing in small groups), and water/feed access during transport—these directly impact arrival condition in unhandled animals
- •Plan regular breaks during long transits (average 34 hours here included resting stops); experienced drivers with well-maintained, ventilated vehicles are essential for welfare outcomes in unbroken stock
- •Pregnant mares presenting with colic carry significant mortality and morbidity risk; elevated lactate and packed cell volume at admission are strong warning signs that warrant aggressive intervention and close monitoring
- •Nearly half of discharged pregnant colic patients develop recurrent colic—close post-discharge monitoring is essential, particularly for Thoroughbreds; consider preventive management protocols
- •Development of diarrhea or SIRS during hospitalization carries very high risk for pregnancy loss—early recognition and intervention (including altrenogest therapy if indicated) may improve outcomes
- •ICU foals maintain relatively neutral intragastric pH for >80% of the time, suggesting routine acid suppression therapy may not be necessary for all neonates
- •Placentitis-exposed foals paradoxically show higher gastric pH and less acidic time, questioning common preventive acid-suppressive protocols in this group
- •Diarrheal foals show increased gastric acidity and may benefit more from targeted acid suppression, but pH management alone does not guarantee survival
- •Diarrhea in horses involves dysbiosis affecting both the mucus layer and intestinal lumen differently—sampling location matters for diagnostic microbiota analysis
- •Monitoring changes in Escherichia, Fusobacterium, and Lactobacillus populations may help identify colitis cases earlier and guide targeted probiotic or antimicrobial interventions
- •Understanding mucosal versus luminal microbiota differences could improve treatment strategies by allowing practitioners to target specific microbial niches in the cecum and colon
- •Recently hospitalized horses should be segregated after discharge and managed with rigorous hygiene practices, regardless of Salmonella status, to prevent transmission to stablemates
- •The presence of diarrhea during hospitalization is a risk factor for Salmonella shedding; implement appropriate biosecurity measures for these horses
- •Owner-implemented biosecurity precautions appear effective at preventing adverse health outcomes from Salmonella shedding in the post-discharge period
- •Early recognition of equine neorickettsiosis severity through bloodwork (hemoglobin, electrolytes, azotemia) helps identify high-risk non-survivors; treat promptly with oxytetracycline
- •Expect laminitis in roughly one-third of cases, often affecting all four feet simultaneously—implement preventive farriery and intensive laminitis management protocols immediately upon diagnosis
- •Monitor electrolyte balance and hydration status closely during hospitalization, as electrolyte loss and hemoconcentration are markers of severe colitis and poor prognosis
- •Monitor hospitalized horses for signs of endotoxemia, particularly those with gastrointestinal or respiratory disease, as early recognition and treatment may prevent secondary laminitis development.
- •Include laminitis prevention protocols when treating conditions associated with endotoxemia (diarrhea, colic surgery, pneumonia) in hospitalized horses.
- •Consider laminitis risk assessment as part of routine monitoring in hospitalized horses, especially those showing evidence of systemic inflammation or gastrointestinal compromise.
- •N. risticii should be considered as a differential diagnosis in mares presenting with abortion, particularly in fetuses showing colitis; seasonal monitoring (May-December) may help identify at-risk pregnancies
- •Fecal PCR testing can detect N. risticii in clinically affected horses during spring-summer months, enabling earlier diagnosis and potential management of pregnant mares exposed to infected animals
- •Genomic characterization shows this pathogen has strain variation; understanding these differences may eventually help predict virulence and abortion risk in future cases
- •Wound infections in Arabian horses are increasingly caused by multidrug-resistant bacteria; conventional antibiotics alone may be ineffective and combination therapies should be considered
- •Bacteriophage therapy shows promise as a practical adjunct to antibiotic treatment for resistant bacterial wound infections, with topical application improving healing timelines
- •Practitioners should maintain awareness of resistance patterns in their region and consider phage-antibiotic combinations when standard antimicrobial protocols fail
- •Fecal microbiota composition and diversity serve as useful biomarkers for monitoring gastrointestinal health in reintroduced wild equines during adaptation periods
- •Elevated stress hormones (cortisol) and immune markers (IgA) alongside dysbiosis may indicate subclinical or clinical diarrhea requiring intervention
- •Supporting beneficial short-chain fatty acid-producing bacteria through dietary management may help prevent or resolve diarrhea in recently released wild horses
- •Reduced microbial diversity in the cecum may be a marker of typhlocolitis; understanding this dysbiosis could inform probiotic or dietary interventions for colitis cases
- •Culture-enriched sequencing offers a viable complementary method to direct sequencing for studying equine gut microbiota in clinical research and diagnostics
- •Fusobacteriota warrants further investigation as a potential pathogenic or indicator organism in equine colitis cases
- •During summer months (July-September) in endemic areas, include PHF in your differential diagnosis for foals presenting with fever, depression, anorexia, diarrhea, and ileus—not just adult horses
- •Submit both blood and feces for PCR testing of Neorickettsia spp. to confirm diagnosis, as clinical signs alone are non-specific
- •PHF in foals is responsive to treatment with appropriate hospitalization and intensive care, so early diagnosis and supportive therapy are warranted
- •NSAIDs are frequently overdosed in horses with RDC; verify dosing protocols and monitor serum albumin concentrations during prolonged NSAID therapy to detect early protein loss
- •Horses presenting with elevated heart rate, high packed cell volume, or abnormal mucous membranes have significantly worse prognosis; consider early aggressive intervention and close monitoring in these cases
- •RDC carries substantial mortality risk (43%); maintain high clinical suspicion in horses with diarrhea, colic, and hypoproteinemia that test negative for infectious causes
- •Salmonella ser. Typhimurium in hospitalized horses may represent zoonotic strains circulating across multiple species; implement strict biosecurity and hygiene protocols to prevent human and other animal exposure
- •Multidrug-resistant Salmonella with extended-spectrum β-lactamase production is emerging in equine practice; routine local antimicrobial susceptibility testing is essential to guide empiric treatment decisions rather than relying on standard protocols
- •Consider Salmonella as a differential diagnosis in hospitalized horses with diarrhea and implement appropriate infection control measures, especially given the public health implications of resistant strains
- •Not applicable to equine practice—this study concerns swine pathology and viral infection in piglets, with no direct translation to horse health or management
- •The hoof lesion presentation (blisters progressing to scabs) differs fundamentally from equine conditions and reflects species-specific viral pathogenesis in pigs
- •No findings or recommendations relevant to equine farriery, veterinary, or performance management disciplines
- •FMT represents an emerging treatment option for geriatric horses with diarrhea, particularly when dysbiosis is suspected, though evidence base is still developing
- •Microbiota profiling can help identify dysbiosis and monitor treatment response, potentially improving outcomes in chronic colitis cases
- •Healthy donor horses can be screened and used as FMT sources, but careful donor selection and microbiota analysis should guide clinical application
- •Gross and microscopic lesions of C. difficile colitis in horses are non-specific and resemble other enteric infections; toxin detection (ELISA) is essential for definitive diagnosis
- •Expect severe hemorrhagic colitis with marked edema and thrombosis on necropsy or biopsy of horses suspected of CDAD
- •Diagnosis cannot be made on pathology alone—always pair histology with C. difficile toxin detection in intestinal samples for accurate diagnosis
- •Recognize that severe, treatment-resistant neonatal diarrhea with hypothermia may indicate congenital neuronal dysplasia rather than infectious colitis alone.
- •This rare developmental condition currently has no clinical diagnostic test available in live horses; diagnosis requires post-mortem histopathology.
- •Understanding this pathology helps explain why some foals with apparent bacterial colitis do not respond to antimicrobial therapy—the primary defect is neuronal architecture, not infection.
- •Transport horses in groups rather than singly when possible, as this significantly reduces behavioral problems during transit
- •Implement hay feeding during transport and ensure proper management practices and safety equipment to minimize health complications like diarrhea and injuries
- •Short journeys (<2 hours) are common in Germany; prioritize stress-reduction strategies during transport regardless of duration, as behavioral issues are reported in one-third of cases
- •IgY passive immunotherapy may offer a non-antibiotic alternative for treating salmonellosis in horses, particularly relevant as multidrug-resistant strains become more common
- •Montanide adjuvant appears effective for producing specific IgY antibodies, potentially offering a more practical production method than traditional Freund's adjuvant
- •While in vitro results are promising, further in vivo clinical trials in horses are needed before implementing this therapy in practice
- •Implement strict biosecurity measures including feed and water sanitation during ECoV outbreaks, as the virus spreads via feco-oral contamination in adult horses
- •Recognize the non-specific clinical presentation (fever, lethargy, anorexia) and request fecal testing via PCR when ECoV is suspected, particularly during known outbreaks
- •Provide supportive care as most cases resolve self-limitingly, but monitor closely for rare but serious complications such as endotoxemia or encephalopathy that indicate compromised intestinal barrier function
- •Current colitis management remains largely symptomatic (fluid/electrolyte balance, laminitis and sepsis prevention) with limited pathogen-specific therapies available
- •Identifying the specific pathogenic cause of colitis is important since different organisms manipulate ion channels differently, potentially allowing future targeted treatments
- •Future research into equine colonic ion channel function may enable development of novel anti-diarrheal treatments beyond current supportive care
- •Use strong ion gap (SIG) analysis in addition to traditional anion gap (AG) assessment when managing horses with acute colitis to better understand acid-base disturbances and guide fluid therapy
- •Monitor plasma electrolytes, protein concentration, and pCO2 concurrently as all three factors directly influence acid-base status and treatment decisions
- •The physicochemical approach provides more detailed interpretation of acid-base abnormalities than traditional methods, potentially improving management of severely colitic horses
Key Research Findings
No clear benefits for probiotic supplementation to improve starch and fiber digestion in horses
No evidence supporting probiotics for colic treatment or salmonellosis prevention
Conflicting results observed for management of scouring in neonatal foals
High doses of novel probiotic species may exacerbate diarrhea and cause adverse events
Multistrain probiotic formulations showed promise for improving aerobic fitness and stamina in exercising horses
Seroprevalence of SBV was 56.5% in camels and 11.3% in donkeys, indicating substantial exposure in both species
Older age was significantly associated with higher SBV seropositivity in both camels (OR=2.3) and donkeys (OR=3.41)
Geographic clustering showed significantly higher odds of seropositivity in camels from Zangon Daura (OR=4.73) and donkeys from Sule Tankarkar (OR=4.46)
Sex, management system, and mixed species rearing did not significantly influence SBV seropositivity
L. intracellularis antibodies detected in 6.3% of rabbits (49/774) and 12.3% of farms (20/163)
L. intracellularis DNA detected in 1.2% of rabbits (8/667) and 3.8% of farms (6/156)
Presence of pigs or horses on farm or neighboring farm significantly increased seropositivity risk (p < 0.05)
History of diarrhea on farm in preceding 3 months significantly increased odds of L. intracellularis positivity (p < 0.05)
Alpha diversity of gut microbiota in diarrheic horses was significantly reduced compared to healthy horses.
Diarrheic horses showed dramatic increases in Bacteroidetes, Verrucomicrobia, and Fibrobacteres phyla, with decreases in Firmicutes, Proteobacteria, and Patescibacteria.
Evidence Base
The Safety, Tolerability and Efficacy of Probiotic Bacteria for Equine Use.
Cooke C Giselle, Gibb Zamira, Harnett Joanna E (2021) — Journal of equine veterinary science
Systematic Review
Schmallenberg virus exposure in camels and donkeys: Potential reservoirs for trans-border spread in the Nigeria-Sahel region.
Adikwu Alex A, Emeto Theophilus I, Horwood Paul F et al. (2025) — Veterinary journal (London, England : 1997)
Cohort Study
Yeh Jung-Yong (2023) — Frontiers in veterinary science
Cohort Study
Comparative Analysis of Gut Microbiota Between Healthy and Diarrheic Horses.
Li Yaonan, Lan Yanfang, Zhang Shuang et al. (2022) — Frontiers in veterinary science
Cohort Study
Dynamic changes of gut fungal community in horse at different health states.
Lan Yanfang, Li Yaonan, Yu Gang et al. (2022) — Frontiers in veterinary science
Cohort Study
Journeys, Journey Conditions, and Welfare Assessment of Unbroken (Unhandled) Horses on Arrival at a Slaughterhouse in Italy.
Zappaterra Martina, Nanni Costa Leonardo, Felici Martina et al. (2022) — Animals : an open access journal from MDPI
Cohort Study
Outcomes of pregnant broodmares treated for colic at a tertiary care facility.
Douglas Hope F, Stefanovski Darko, Southwood Louise L (2021) — Veterinary surgery : VS
Cohort Study
Intragastric pH of foals admitted to the intensive care unit.
Wise Jessica C, Raidal Sharanne L, Wilkes Edwina J A et al. (2020) — Journal of veterinary internal medicine
Cohort Study
Luminal and Mucosal Microbiota of the Cecum and Large Colon of Healthy and Diarrheic Horses.
Arroyo Luis G, Rossi Laura, Santos Bruna P et al. (2020) — Animals : an open access journal from MDPI
Cohort Study
Factors associated with equine shedding of multi-drug-resistant Salmonella enterica and its impact on health outcomes.
Burgess B A, Bauknecht K, Slovis N M et al. (2018) — Equine veterinary journal
Cohort Study
Clinical and clinicopathological factors associated with survival in 44 horses with equine neorickettsiosis (Potomac horse Fever).
Bertin F R, Reising A, Slovis N M et al. (2013) — Journal of veterinary internal medicine
Cohort Study
Risk factors for development of acute laminitis in horses during hospitalization: 73 cases (1997-2004).
Parsons, Orsini, Krafty et al. (2007) — Journal of the American Veterinary Medical Association
Cohort Study
Detection of Neorickettsia risticii in antemortem fecal and postmortem fetal samples, with genomic insights from complete genome sequencing of a strain recovered from an aborted equine fetus.
Tirth Uprety, Jacob Durazo, Litty Paul et al. (2025) — Veterinary microbiology
Case Report
Controlling drug-resistant bacteria in Arabian horses: bacteriophage cocktails for treating wound infections.
Khalid Esraa, Tartor Yasmine H, Ammar Ahmed M et al. (2025) — Frontiers in veterinary science
Case Report
Li Zhenghao, Luo Zhengwei, Hu Defu (2024) — Animals : an open access journal from MDPI
Case Report
Direct and culture-enriched 16S rRNA sequencing of cecal content of healthy horses and horses with typhlocolitis.
Zakia Luiza S, Gomez Diego E, Caddey Benjamin B et al. (2023) — PloS one
Case Report
Diagnosis of Potomac horse fever (syn. equine neorickettsiosis) in 2 foals in southwestern Ontario.
Rosalie Fortin-Trahan, E. Sjolin, A. Lack et al. (2023) — The Canadian veterinary journal = La revue veterinaire canadienne
Case Report
Right dorsal colitis in horses: A multicenter retrospective study of 35 cases.
Flood Jordan, Byrne David, Bauquier Jennifer et al. (2023) — Journal of veterinary internal medicine
Case Report
Bustos Carla P, Dominguez Johana E, Garda Daniela et al. (2021) — Journal of equine veterinary science
Case Report
Pathogenicity Analysis of Weaned Piglets Challenged With Novel Emerging Senecavirus A in Fujian, China.
Liu Cun, Liu Yanhan, Li Xiubo et al. (2021) — Frontiers in veterinary science
Case Report
Show 8 more references
The fecal microbiota of healthy donor horses and geriatric recipients undergoing fecal microbial transplantation for the treatment of diarrhea.
McKinney Caroline A, Oliveira Bruno C M, Bedenice Daniela et al. (2020) — PloS one
Case Report
Pathology and diagnostic criteria of Clostridium difficile enteric infection in horses.
Diab S S, Rodriguez-Bertos A, Uzal F A (2013) — Veterinary pathology
Case Report
Enteric dysganglionosis resembling intestinal neuronal dysplasia in a foal with bacterial colitis.
Giri D K, Quist E M, Ambrus A et al. (2010) — Veterinary pathology
Case Report
A survey of welfare problems associated with transporting horses by road in Germany (2022-2024).
May Anna, Riley Christopher B, Scharre Annabel et al. (2025) — Veterinary journal (London, England : 1997)
Expert Opinion
In vitro Inhibitory Activity of IgY Antibodies Against Salmonella Ser. Newport Isolated from Horses.
Bustos Carla P, Leiva Carlos L, Gambarotta Mariana et al. (2021) — Journal of equine veterinary science
Expert Opinion
Enteric coronavirus infection in adult horses.
Pusterla N, Vin R, Leutenegger C M et al. (2018) — Veterinary journal (London, England : 1997)
Expert Opinion
Equine Laminitis : A Review -
R. H. Bhatt, N. Kelawala, D. Suthar et al. (2014) — Journal of Veterinary Advances
Expert Opinion
Physicochemical interpretation of acid-base abnormalities in 54 adult horses with acute severe colitis and diarrhea.
Gomez D E, Arroyo L G, Stämpfli H R et al. (2013) — Journal of veterinary internal medicine
Expert Opinion