ISSN 2398-2977      

Diarrhea: idiopathic



  • Cause: by its very nature the exact etiology behind idiopathic diarrhea is unknown. The diagnostic evaluation should revolve around ensuring all common differential diagnoses are ruled out.
  • Signs: often mild in nature it can range to severe. Owner will often complain about increased fecal water or diarrhea during exercise.
  • Diagnosis: this is a diagnosis of exclusion and all tests associated with other causes of diarrhea should be performed including hematology, biochemistry, fecal analysis, ultrasonography.
  • Treatment: challenging without a known etiology with efforts made towards symptomatic treatment.
  • Prognosis: good to excellent if signs are mild and will often be perceived as a more significant problem by the client.



  • See the differentials list for causes of diarrhea.
  • An etiology for idiopathic diarrhea cannot be stated due to its very nature.

Predisposing factors


  • Unknown but diarrhea is often associated with dietary changes, stress, drug administration (in particular antibiotics and nonsteroidal anti-inflammatory drugs) and in specific cases can be due to an infectious etiology.


  • Dysbiosis can lead to disruption of the normal flora of the intestine leading to:
    • Abnormal carbohydrate metabolism.
    • Decreased metabolism of bile acids.
    • Abnormal GI motility.
    • Blunting of intestinal villi.
  • Altered carbohydrate metabolism leads to reduction in the production of short-chain fatty acids (SCFA). SCFAs are intrinsically linked with fluid and electrolyte absorption and therefore a sudden drop leads to intraluminal accumulation of electrolytes and carbohydrates thus leading to an oncotic, secretory diarrhea.
  • Bile acids are colonic secretagogues and therefore, when accumulating, can lead to increased luminal fluid.
  • Rapid dietary changes can induce a change in the microbiota of the caecum leading to all of the above abnormalities.
  • Malabsorptive diarrhea: absorption is controlled by the surface epithelium cells.
  • Secretory diarrhea: the secretory role of the colon is controlled by the crypt epithelium. In normal circumstances the secretion is outweighed by the absorptive capacity of the colon:
    • Controlled by four paths: hormonal, enteric nervous system, bacterial enterotoxins and the immune system.
    • Bacterial enterotoxins increase cAMP or cGMP production leading to an increase in secretion.
    • Inflammatory mediators (histamine, prostaglandins, cytokines, etc) can directly stimulate enterocytes or activate the enteric nervous system leading to secretory responses.
  • Inflammatory cell mediators released from mast cells, monocytic or granulocytic phagocytes can induce chloride and water secretion and reduce sodium and chloride absorption.
  • Phagocyte derived reactive oxygen metabolites are released in response to inflammation, trauma or ischemia and these lead to chloride secretion.
  • Ileus can often occur as a sequalae to diarrhea and therefore gut motility should be monitored closely by auscultation and/or ultrasonography.
  • Free fecal water has no definitive cause but could be associated with diet or stress. Changes in the diet to an improved fiber quality can help.


  • No specific timecourse as the etiology is unknown.


This article is available in full to registered subscribers

Sign up now to obtain ten tokens to view any ten Vetlexicon articles, images, sounds or videos, or Login


This article is available in full to registered subscribers

Sign up now to obtain ten tokens to view any ten Vetlexicon articles, images, sounds or videos, or Login


This article is available in full to registered subscribers

Sign up now to obtain ten tokens to view any ten Vetlexicon articles, images, sounds or videos, or Login


This article is available in full to registered subscribers

Sign up now to obtain ten tokens to view any ten Vetlexicon articles, images, sounds or videos, or Login

Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Shaw S D & Stämpfli H (2018) Diagnosis and treatment of undifferentiated and infectious acute diarrhea in the adult horse. Vet Clin Equine Pract 34 (1), 39-53 PubMed.
  • Matthews J B (2014) Anthelmintic resistance in equine nematodes. Int J Parasitol Drugs Drug Resistance 4 (3), 310-315 PubMed.
  • Chapman A (2009) Acute diarrhea in hospitalized horses. Vet Clin North Am Equine Pract 25 (2), 363-380 PubMed.
  • Hassel D M, Smith P A, Nieto J E, Beldomenico P & Spier S J (2009) Di-tri-octahedral smectite for the prevention of post-operative diarrhea in equids with surgical disease of the large intestine: results of a randomized clinical trial. Vet J 182, 210-214 PubMed.
  • McGorum B C & Pirie R S (2009) Antimicrobial associated diarrhea in the horse. Part 1: Overview, pathogenesis and risk factors. Equine Vet Educ 21 (11), 610-616 VetMedResource.
  • Hillyer M (2004) A practical approach to diarrhea in the adult horse. In Pract 26 (1), 2-11 VetMedResource.

Other sources of information

  • Reed S, Bayly W & Sellon D (2010) Equine Internal Medicine. 3rd edn. Saunders Elsevier, USA.


Abdomen: distention

Abdomen: pain - adult

Abdomen: peritonitis

Acid-base imbalance


Blood: biochemistry - albumin

Blood: biochemistry - bile acids

Blood: biochemistry - creatinine

Blood: biochemistry - gamma glutamyl transferase (gGT)

Blood: biochemistry - glutamate dehydrogenase

Blood: biochemistry - iron

Blood: biochemistry - overview

Blood: biochemistry - urea

Blood: overview

Blood: transfusion

Chronic inflammatory bowel disease

Clostridia spp

Codeine phosphate

Colon: colitis

Diarrhea: antimicrobial associated

Diarrhea: parasitic

Disseminated intravascular coagulation

Endotoxemia: overview

Enzyme linked immunosorbent assay (ELISA)

Equine coronavirus infection

Feces: bacteriology

Feces: parasitology - McMaster worm egg count

Fluid therapy: diarrhea

Foot: laminitis

Gastrointestinal: clostridiosis

Gastrointestinal: neoplasia

Gastrointestinal: sand colic

Heart: failure - overview





Hypovolemic shock

Intestine: salmonellosis


Kidney: disease - overview

Large colon: intussusception


Liver disease: overview

Muscle: myopathy - atypical

Nutrition: probiotics

Plasma: fibrinogen

Polymerase chain reaction (PCR)

Potomac Horse Fever

Pyrexia: overview

Radiography: overview

Rectum: biopsy


Salmonella spp

Serum amyloid A


Strongyle infestation: large

Teeth: dental disease - overview

Therapeutics: anti-inflammatory drugs

Therapeutics: antimicrobials

Therapeutics: gastrointestinal system

Therapeutics: glucocorticoids

Therapeutics: parasiticides

Toxicity: non-steroidal anti-inflammatory (NSAID)

Ultrasonography: abdomen

Want more related items, why not
contact us

Can’t find what you’re looking for?

We have an ever growing content library on Vetlexicon so if you ever find we haven't covered something that you need please fill in the form below and let us know!


To show you are not a Bot please can you enter the number showing adjacent to this field

 Security code