Colitis: What the Research Says
Evidence from 20 peer-reviewed studies
What Professionals Should Know
- •Recognize that antibiotic use is a major dysbiosis risk factor—consider microbiota-sparing alternatives and use fecal microbiota transplantation or probiotics as preventive/therapeutic options for colitis cases
- •Understand that individual variation in microbiota composition is normal; baseline characterization may help detect clinically relevant dysbiosis in problem cases
- •Diet and management factors significantly influence microbiota—dietary adjustments and environmental consistency should be primary interventions before considering microbial modulation therapies
- •FMT appears effective for treating colitis in hospitalized horses, producing clinically meaningful improvements in diarrhea scores and manure consistency
- •Consider FMT as part of standard care protocols for moderate to severe colitis, as treated horses show faster day-to-day improvement trajectories
- •Microbiota diversity correlates with clinical improvement—horses with better manure consistency show healthier fecal microbiomes, supporting the biological rationale for microbiota-modulating therapies
- •Both traditional and selective NSAIDs cause temporary but significant disruption to the hindgut microbiota—minimize treatment duration when possible and monitor for GI signs during and after therapy
- •NSAID dysbiosis resolves within 2 weeks of stopping treatment, but timing matters if the horse is already at risk for colic or colitis
- •Consider probiotic or prebiotic support during NSAID courses, particularly in horses with prior GI disease, to help maintain microbial stability
- •Machine learning-based prognostic tools using readily available clinical data plus viscoelastic testing may help identify horses with colic at highest mortality risk earlier in treatment
- •L-lactate concentration should remain a critical component of prognostic assessment in acute colic cases, as it provides strong predictive value across multiple model types
- •Viscoelastic coagulation testing adds predictive value when combined with clinical variables in ML models, but coagulopathy diagnosis alone is insufficient for survival prediction and should not be used as a standalone prognostic indicator
- •Microbiota composition differs significantly between healthy and colitic horses, but these differences have limited predictive value for laminitis development or survival during hospitalization
- •While certain bacterial taxa (particularly Enterobacteriaceae) are associated with adverse outcomes in colitis, microbiota analysis alone appears insufficient as a prognostic indicator for individual cases
- •Therapeutic strategies targeting microbiota restoration in colitic horses may focus on restoring beneficial taxa (Faecalibacterium, Ruminococcaceae, Lachnospiraceae) rather than preventing laminitis or improving survival
- •Dietary grain content moderately influences equine fecal microbiota, but disease state (particularly antimicrobial-associated colitis) has substantially greater impact on microbial composition and diversity
- •Horses treated with antimicrobials causing diarrhea develop more severe dysbiosis than those with Salmonella infection, suggesting different therapeutic or management approaches may be warranted
- •Microbiome analysis could help differentiate between antimicrobial-associated diarrhea and infectious causes like Salmonella, potentially guiding treatment decisions
- •Horses receiving NSAIDs for >4 days should be monitored closely for signs of colitis (depression, reduced appetite, unstructured feces, abdominal pain) starting from day 2 of treatment, as colon pathology develops early and may be subclinical
- •Ultrasonographic measurement of right dorsal colon wall thickness is a useful noninvasive monitoring tool during NSAID treatment, with significant thickening indicating pathology before clinical signs appear
- •Consider implementing routine monitoring protocols (clinical examination, ultrasonography, fecal occult blood testing) for hospitalized horses receiving NSAIDs to detect early colon changes and allow timely intervention
- •A positive fecal or blood test for a single enteric pathogen in a colitis case may carry worse prognostic implications than multiple detections or negative results; interpret single-agent positives cautiously
- •Multiple pathogen detection should not be used to predict prolonged hospitalization or increased costs in colitis cases
- •Testing laboratory choice and methodology significantly impact detection rates; compare results cautiously across different diagnostic facilities
- •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
- •Implement prophylactic digital cryotherapy in colitis cases as a cost-effective, evidence-based strategy to reduce clinical laminitis incidence by approximately 70%
- •Use systemic inflammatory markers (respiratory rate, blood lactate) to identify high-risk colitis patients who would most benefit from ICE protocols
- •Recognize that laminitis development in colitis cases dramatically worsens prognosis; early intervention with cryotherapy is justified as a preventive measure
- •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
- •Test faecal samples from horses with acute diarrhoea for C. difficile toxins and enterotoxigenic C. perfringens, as these pathogens are strongly associated with equine colitis and may guide treatment decisions
- •Presence of C. difficile toxins in diarrhoeic horses indicates a more serious prognosis; affected animals require closer monitoring and potentially more aggressive supportive care
- •Culture of C. perfringens alone is insufficient for diagnosis—toxin testing is essential as only 60-64% of isolated C. perfringens strains produce enterotoxin
- •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
- •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
- •Horses with colitis develop delayed neutrophil apoptosis that may perpetuate systemic inflammation; monitoring neutrophil counts and inflammatory markers may help identify and manage SIRS development
- •Understanding that neutrophil lifespan is prolonged in colitis cases suggests that anti-inflammatory interventions targeting apoptosis pathways could be therapeutic targets in managing equine colitis-associated SIRS
- •The concentration-dependent delay in apoptosis implies that neutrophilia itself may exacerbate the inflammatory cascade in colitis, reinforcing the need for aggressive management of the primary colitis lesion
- •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
- •Intestinal hyperammonaemia should be considered in horses and foals presenting with colic, diarrhoea, or neurological signs; blood ammonium concentration at admission is the most reliable prognostic indicator
- •Affected horses commonly show tachycardia, elevated PCV, and metabolic derangements (hyperlactataemia, hyperglycaemia) that guide supportive care decisions
- •Survivors have excellent long-term prognosis with complete recovery and return to function, justifying aggressive treatment despite severe initial presentation
- •Misoprostol, already used clinically as a gastroprotectant in horses, may have additional anti-inflammatory benefits through neutrophil modulation in inflammatory conditions like laminitis and colitis
- •These in vitro findings suggest misoprostol could potentially reduce tissue damage from dysregulated neutrophil activity when NSAIDs alone are insufficient, though in vivo clinical trials are needed
- •Further research is required before misoprostol can be recommended as a novel anti-inflammatory therapy, but this work provides a mechanistic rationale for investigating its use beyond GI protection
- •Foals are uniquely susceptible to severe jejunal involvement with C. difficile; consider this diagnosis in antibiotic-treated foals with diarrhea involving the small intestine
- •Age and species dramatically influence disease presentation and severity—young horses show different lesion patterns than other species, requiring species-specific diagnostic and treatment approaches
- •Antibiotic administration remains a primary risk factor; minimize unnecessary antibiotic use in horses, particularly neonates, to reduce C. difficile-associated disease risk
- •Selective COX-2 inhibitors (e.g. etodolac) may be safer than nonselective NSAIDs for horses with colonic disease or at risk of colitis, as they preserve COX-1 activity without increasing mucosal permeability
- •Nonselective COX inhibitors like flunixin can increase intestinal permeability in normal tissue, which may predispose to colitis in susceptible horses
- •While NSAID use does not directly impair colonic repair after bile injury, the increased permeability with nonselective inhibitors warrants careful patient selection and monitoring
Key Research Findings
Age, diet, antibiotic administration, and geographic location significantly affect equine gut microbiota composition
High intra- and inter-individual variability in equine fecal microbiota complicates dysbiosis interpretation and establishment of clear diagnostic criteria
Dysbiosis may play a role in pathogenesis of colitis and asthma, though definitive causal relationships remain unclear
Prebiotics, probiotics, and fecal microbiota transplantation show potential for preventing or treating dysbiosis-related diseases such as antibiotic-induced colitis
FMT-treated horses showed greater reduction in diarrhea score (4±3 grades) compared to untreated controls (1.5±3 grades, P=0.021)
FMT recipients demonstrated higher day-over-day improvement incidence (61% vs 36%, P=0.011)
FMT-treated horses showed greater microbiota normalization with lower UniFrac distance to healthy controls (0.53±0.27 vs 0.62±0.26, P<0.001)
Improved manure consistency was associated with greater alpha-diversity in colitic horses at both locations (r=-0.385 to -0.479, P<0.01)
Both phenylbutazone (non-selective COX inhibitor) and firocoxib (COX-2-selective) decreased fecal microbiota diversity in horses over 10 days of treatment
Microbiota alterations were most pronounced at day 10 of NSAID administration, with partial recovery by day 25
Both drug classes caused similar dysbiotic effects despite different COX selectivity profiles
NSAID-induced dysbiosis may contribute to colic, colitis, enteric infections, and laminitis in horses
Random forest machine learning models achieved 91% sensitivity and 83% specificity for survival prediction compared to GLM at 65% sensitivity and 42% specificity
L-lactate remains a key independent predictor of survival in horses with acute abdominal pain
Coagulopathy diagnosis alone performed poorly for survival prediction (AUC = 0.515) with 81% sensitivity but only 31% specificity
Evidence Base
Current Understanding of Equine Gut Dysbiosis and Microbiota Manipulation Techniques: Comparison with Current Knowledge in Other Species.
Boucher Laurie, Leduc Laurence, Leclère Mathilde et al. (2024) — Animals : an open access journal from MDPI
Assessment of clinical and microbiota responses to fecal microbial transplantation in adult horses with diarrhea.
McKinney Caroline A, Bedenice Daniela, Pacheco Ana P et al. (2021) — PloS one
Differential effects of selective and non-selective cyclooxygenase inhibitors on fecal microbiota in adult horses.
Whitfield-Cargile Canaan M, Chamoun-Emanuelli Ana M, Cohen Noah D et al. (2018) — PloS one
Integration of machine learning and viscoelastic testing to improve survival prediction in horses experiencing acute abdominal pain at a veterinary teaching hospital.
Macleod, Wilkins, McCoy et al. (2025) — Equine veterinary journal
Fecal microbiota of horses with colitis and its association with laminitis and survival during hospitalization.
Ayoub Cosette, Arroyo Luis G, MacNicol Jennifer L et al. (2022) — Journal of veterinary internal medicine
The effects of signalment, diet, geographic location, season, and colitis associated with antimicrobial use or Salmonella infection on the fecal microbiome of horses.
Arnold Carolyn E, Pilla Rachel, Chaffin M Keith et al. (2021) — Journal of veterinary internal medicine
Colonic Health in Hospitalized Horses Treated with Non-Steroidal Anti-Inflammatory Drugs - A Preliminary Study.
van Galen G, Saegerman C, Hyldahl Laursen S et al. (2021) — Journal of equine veterinary science
Detection of pathogens in blood or feces of adult horses with enteric disease and association with outcome of colitis.
Kopper Jamie J, Willette Jaclyn A, Kogan Clark J et al. (2021) — Journal of veterinary internal medicine
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
Prophylactic digital cryotherapy is associated with decreased incidence of laminitis in horses diagnosed with colitis.
Kullmann, Holcombe, Hurcombe et al. (2015) — Equine veterinary journal
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
A prospective study of the roles of clostridium difficile and enterotoxigenic Clostridium perfringens in equine diarrhoea.
Weese J S, Staempfli H R, Prescott J F (2001) — Equine veterinary journal
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
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
Neutrophil apoptosis is delayed in an equine model of colitis: Implications for the development of systemic inflammatory response syndrome.
Anderson S L, Singh B (2017) — Equine veterinary journal
Pathology and diagnostic criteria of Clostridium difficile enteric infection in horses.
Diab S S, Rodriguez-Bertos A, Uzal F A (2013) — Veterinary pathology
Putative intestinal hyperammonaemia in horses: 36 cases.
Dunkel B, Chaney K P, Dallap-Schaer B L et al. (2011) — Equine veterinary journal
Martin Emily Medlin, Till Rebecca Louise, Sheats Mary Katherine et al. (2017) — Frontiers in veterinary science
The comparative pathology of Clostridium difficile-associated disease.
Keel M K, Songer J G (2006) — Veterinary pathology
The effects of cyclo-oxygenase inhibitors on bile-injured and normal equine colon.
Campbell N B, Jones S L, Blikslager A T (2002) — Equine veterinary journal