Diarrhoea: What the Research Says
Evidence from 22 peer-reviewed studies
What Professionals Should Know
- •Consider using threshold-based deworming for mares (treating only when faecal egg counts exceed 300 epg) as an effective alternative to routine prophylactic treatments, reducing anthelmintic use and selection pressure for resistance
- •In foals, less frequent deworming (2 treatments vs. monthly) may not adequately control ascarid populations—monthly or strategic deworming may still be warranted for young stock to manage parasite burdens and development
- •Monitoring bodyweight and general health indicators alongside parasite control can help identify whether reduced treatment intensity is sustainable on your farm without negative clinical outcomes
- •When treating piroplasmosis with imidocarb in horses, anticipate gastrointestinal complications including colic and diarrhoea as common adverse effects
- •Anticholinergic medications may help manage imidocarb side effects but require careful clinical monitoring to avoid paradoxical gastrointestinal motility problems
- •Consider the risk-benefit profile of anticholinergic prophylaxis or treatment in individual cases, weighing gastrointestinal benefits against potential ileus risk
- •Expect complications in approximately 1 in 6 horses undergoing MRI under general anaesthesia; pyrexia, pneumonia and colic are the most likely complications to monitor for in recovery
- •Consider peri-anaesthetic antimicrobial administration as a risk-mitigation strategy, particularly for horses at higher risk of anaesthetic complications
- •Be alert for delayed complications including pyrexia and pneumonia in the post-operative period, as these represented the majority of complications in this cohort
- •Counsel owners that approximately 2 in 3 horses will return to work by 6 months and 3 in 4 by one year, but only about half will match preoperative performance levels early on
- •Horses with previous colic surgery, orthopaedic conditions requiring stall rest, or those developing post-operative complications (hernia, diarrhoea, laminitis) have significantly reduced return-to-use prospects and require modified expectations
- •Implement targeted rehabilitation protocols and early intervention for post-operative complications (especially incisional hernioplasty) to optimize functional recovery outcomes
- •Surgical management of DPJ reduces nasogastric reflux burden but increases risk of post-operative diarrhoea and incisional complications—weigh reflux control benefits against these risks
- •Post-operative infection surveillance should be intensified in DPJ surgery cases given elevated incisional infection rates compared to other abdominal procedures
- •Medical management may be preferable for horses where minimizing post-operative complications outweighs the benefits of reduced reflux volume and duration
- •Antibiotic use is a significant risk factor for C. difficile colitis in adult horses; clinicians should use narrow-spectrum antimicrobials when possible and monitor treated horses closely for diarrhoea
- •Young foals naturally colonize with C. difficile in the first two weeks of life, but this typically self-resolves; avoid unnecessary antimicrobial treatment in neonates to prevent pathogenic overgrowth
- •Environmental contamination is higher on studfarms with foals; implement enhanced hygiene protocols during foaling season to reduce transmission risk between animals
- •SAA can aid in differentiating bacterial from non-bacterial infections in neonatal foals, particularly those presenting with weakness—normal SAA suggests non-bacterial disease and better prognosis
- •SAA normalizes faster than traditional markers (fibrinogen, WBC count) during recovery from Rhodococcus equi pneumonia, making it useful for monitoring treatment response and discharge planning
- •SAA is not reliably useful for evaluating foals with diarrhoea as the primary sign, regardless of rotavirus status, so should be combined with other diagnostic approaches for this condition
- •Reference ranges for ionised calcium in heparinised blood for normal horses are established (1.43–1.75 mmol/l), useful for clinical laboratories assessing calcium status in colic and diarrhoea cases
- •Heparinised blood samples are stable for ionised calcium analysis over extended storage periods, allowing flexibility in sample handling and transport to reference laboratories
- •A validated pH-adjustment formula is now available to standardize ionised calcium results to pH 7.4, improving comparability of results across different disease states and clinical settings
- •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
- •Cryptosporidium is a recognised cause of diarrhoea in racehorses and should be included in differential diagnoses for diarrhoeic horses in China
- •Molecular detection methods are available for diagnosis; consider testing racehorses with persistent or unexplained diarrhoea
- •Increased awareness of Cryptosporidium prevalence in racing populations may inform management and biosecurity protocols on studs and training facilities
- •IBD in horses involves pathological changes to the enteric nervous system, specifically loss of interstitial cells of Cajal that function as gastrointestinal pacemakers, which may explain motility disturbances and clinical signs
- •Understanding ICC depletion in equine IBD may guide future therapeutic strategies targeting gastrointestinal function and neurological dysfunction
- •Clinical presentations of weight loss, diarrhoea and colic in horses with IBD may be linked to structural changes in enteric pacemaker cells and supporting neural tissue
- •Surgical excision of infected or patent umbilical remnants has good outcomes (89% survival), but foals with concurrent septic arthritis/physitis require careful prognostic counseling due to significantly worse survival
- •Minimize anaesthesia time and optimize passive transfer status preoperatively to reduce post-operative complication risk
- •Be alert for concurrent infectious conditions (present in 60.6% of cases) before surgery, particularly diarrhoea and joint/bone infections, as these substantially impact prognosis
- •Grazing horses should be monitored closely during autumn months (particularly September-November) in tree-bordered or tree-containing pastures, especially in continental Europe; consider reduced grazing time or alternative management during high-risk periods
- •AM presents with variable clinical signs including muscle weakness, gastrointestinal signs, and renal dysfunction; clinicians should maintain high suspicion in autumn-affected grazing horses regardless of age or breed
- •Environmental management focused on pasture characteristics (proximity to trees) and grazing duration may help reduce AM incidence; further case-control studies needed to confirm causal relationships
- •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
- •Include proliferative enteropathy in the differential diagnosis for weanling foals presenting with rapid weight loss, diarrhoea, colic and hypoproteinaemia, particularly in outbreak situations on breeding farms.
- •Consider erythromycin estolate ± rifampin as effective treatment for suspected equine PE, with prolonged therapy (≥21 days) required for clinical recovery.
- •Use faecal PCR and serology (antibody testing) for antemortem diagnosis alongside clinical signs and biochemical findings; hypoproteinaemia is a consistent marker of the disease.
- •FMT solutions can be safely prepared and stored at 4°C for up to 3 days or frozen at -20°C for up to 28 days without losing therapeutic efficacy, providing flexibility in clinical scheduling and batch preparation
- •The stability of FMT during storage means practitioners can prepare solutions in advance or transport them to referral facilities without compromising the microbial composition
- •This in vitro data supports the practical use of FMT as a treatment option for equine diarrhoea and dysbiosis, though clinical efficacy studies are still needed
- •Establish and implement written antimicrobial protocols in your practice to align prescribing with best evidence, as this was identified as a key decision-making factor by practitioners
- •Consider that bacterial culture results and formal guidelines should drive antimicrobial selection rather than routine empirical prescribing, particularly for conditions like wound infections
- •Advocate for expanded oral antibiotic options and clearer treatment guidelines at industry and regulatory levels to improve antimicrobial stewardship in equine practice
- •Understanding antimicrobial susceptibilities of L. intracellularis is essential for effective EPE treatment protocols in equine practice
- •Cell culture isolation methods are necessary to properly test antimicrobial efficacy against this obligate intracellular pathogen
- •Early diagnosis and targeted antimicrobial therapy based on susceptibility data can improve outcomes in horses with proliferative enteropathy
- •Recognise ECoV in adult horses presenting with fever, depression, and anorexia; submit faecal samples for qPCR confirmation rather than relying on clinical signs alone
- •Implement strict biosecurity protocols including faecal-oral precautions, as no specific vaccine or immunoprophylactic measures are currently available for horses
- •Monitor for complications such as endotoxaemia and hyperammonaemia-associated encephalopathy in infected horses, as these significantly impact prognosis beyond the primary viral infection
- •Inspect alfalfa hay carefully for dodder contamination before feeding; even small amounts can cause clinical signs within 36 hours
- •Watch for sudden onset of diarrhoea, inappetence, and neurological signs in multiple horses on the same premises, and investigate feed quality immediately
- •Removing contaminated feed is the primary treatment; horses typically recover fully within 3 days without additional intervention
- •Suspect EPE in weanling foals presenting with fever, lethargy, diarrhoea and colic; use combination of ultrasound, serology and faecal PCR for diagnosis rather than relying on single diagnostic method
- •Monitor for hypoproteinaemia and intestinal wall thickening on ultrasound as key diagnostic indicators of EPE in affected foals
- •Implement biosecurity and management practices focused on weanling foal groups, as this age group is at highest risk of EPE
- •Suspect EPE in weanling foals presenting with diarrhoea, colic, lethargy and peripheral oedema; use combination of blood work, abdominal ultrasound, serology and faecal PCR for definitive diagnosis
- •Clinical management and treatment protocols for EPE are established and available, making this a manageable condition if diagnosed promptly
- •Monitor at-risk foal populations around weaning time and maintain awareness of this emerging disease in your region
Key Research Findings
Reduced-intensity deworming protocols (2 treatments vs. monthly) in foals resulted in no significant bodyweight differences between groups over 6 months
Foals receiving only 2 anthelmintic treatments (FA group) had significantly higher ascarid and strongylid egg counts than monthly-treated foals (FB group)
Mares dewormed on an as-needed basis (MB group, when egg counts exceeded 300 epg) showed no significant parasite burden differences compared to fixed-schedule protocols
Health incidents (colic and diarrhoea) were rare across all treatment groups, suggesting reduced treatment intensity did not compromise welfare over the study period
Imidocarb dipropionate causes colic and diarrhoea in horses as documented adverse effects
Atropine and glycopyrrolate are anticholinergic agents that may ameliorate imidocarb-induced gastrointestinal adverse effects
Both anticholinergic agents carry risk of inhibiting gastrointestinal motility, potentially causing iatrogenic ileus and colic
Post-anaesthetic complications occurred in 17.4% (51/293) of horses undergoing MRI under general anaesthesia, with pyrexia being most common (n=35)
Peri-anaesthetic antimicrobial administration reduced odds of post-anaesthetic complications by 71% (OR 0.29, p=0.002)
Peri-anaesthetic antimicrobials reduced odds of pyrexia by 77% (OR 0.23, p=0.005), while increased age was protective against pyrexia
At 6 months post-celiotomy, 68% of horses (133/195) returned to intended use and 54% (85/156) reached or exceeded preoperative performance levels
By one year, return to use improved to 76% (145/190) with 66% (101/153) at or above preoperative performance
Previous celiotomy, stall rest for orthopaedic conditions, nonstrangulating lesion type, incisional hernia, diarrhoea, and laminitis were significant negative prognostic factors
Overall prognosis for return to use and performance following colic surgery is fair to good despite multiple risk factors affecting outcomes
Surgically treated horses with DPJ had shorter duration, smaller volume, and slower rate of nasogastric reflux compared to medically managed cases
Evidence Base
Monitoring equine ascarid and cyathostomin parasites: Evaluating health parameters under different treatment regimens.
Nielsen Martin K, Gee Erica K, Hansen Alyse et al. (2021) — Equine veterinary journal
Comparison of glycopyrrolate and atropine in ameliorating the adverse effects of imidocarb dipropionate in horses.
Donnellan C M B, Page P C, Nurton J P et al. (2013) — Equine veterinary journal
Incidence and risk factors for complications associated with equine general anaesthesia for elective magnetic resonance imaging.
Morgan Jessica M, Aceto Helen, Manzi Timothy et al. (2024) — Equine veterinary journal
Return to use and performance following exploratory celiotomy for colic in horses: 195 cases (2003-2010).
Davis W, Fogle C A, Gerard M P et al. (2013) — Equine veterinary journal
Complications and survival associated with surgical compared with medical management of horses with duodenitis-proximal jejunitis.
Underwood C, Southwood L L, McKeown L P et al. (2008) — Equine veterinary journal
Clostridium difficile: prevalence in horses and environment, and antimicrobial susceptibility.
Båverud V, Gustafsson A, Franklin A et al. (2003) — Equine veterinary journal
Serum amyloid A (SAA) as an aid in the management of infectious disease in the foal: comparison with total leucocyte count, neutrophil count and fibrinogen.
Hultén C, Demmers S (2002) — Equine veterinary journal
Heparinised blood ionised calcium concentrations in horses with colic or diarrhoea compared to normal subjects.
van der Kolk J H, Nachreiner R F, Refsal K R et al. (2002) — Equine veterinary journal
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
Molecular detection and genetic characteristics of Cryptosporidium spp. in Chinese racehorses.
Xu Chunyan, Wei Zilin, Tan Feng et al. (2023) — Equine veterinary journal
Myenteric networks of interstitial cells of Cajal are reduced in horses with inflammatory bowel disease.
Fintl C, Lindberg R, McL Press C (2020) — Equine veterinary journal
Short-term outcome and risk factors for post-operative complications following umbilical resection in 82 foals (2004-2016).
Reig Codina L, Werre S R, Brown J A (2019) — Equine veterinary journal
European outbreaks of atypical myopathy in grazing equids (2006-2009): spatiotemporal distribution, history and clinical features.
van Galen G, Marcillaud Pitel C, Saegerman C et al. (2012) — Equine veterinary journal
Putative intestinal hyperammonaemia in horses: 36 cases.
Dunkel B, Chaney K P, Dallap-Schaer B L et al. (2011) — Equine veterinary journal
Equine proliferative enteropathy: a cause of weight loss, colic, diarrhoea and hypoproteinaemia in foals on three breeding farms in Canada.
Lavoie J P, Drolet R, Parsons D et al. (2000) — Equine veterinary journal
Storage of equine faecal microbiota transplantation solution has minimal impact on major bacterial communities and structure.
Bell J, Raidal S, Peters A et al. (2024) — Veterinary journal (London, England : 1997)
Usage of Antimicrobials in Equine Veterinary Practice in Denmark - A Case-Based Survey.
Jacobsen Alice B J E, Damborg Peter, Hopster-Iversen Charlotte (2023) — Journal of equine veterinary science
In vitro antimicrobial activity against equine Lawsonia intracellularis strains.
Pereira C E R, Resende T P, Vasquez E et al. (2019) — Equine veterinary journal
Equine coronavirus: An emerging enteric virus of adult horses.
Pusterla N, Vin R, Leutenegger C et al. (2016) — Equine veterinary education
Alfalfa dodder (Cuscuta campestris) toxicity in horses: clinical, haematological and serum biochemical findings.
Abutarbush S M (2013) — The Veterinary record