7. Diarrhea in Adult Horses and Foals

1/20/2026

Acute inflammation and mucosal injury to the colon that often precipitates and accompanies diarrhea

colitis

Colitis may include cecum (_________) and small intestine (_______)

May include cecum (TYPHLOCOLITIS) and small intestine (ENTEROCOLITIS)

what is the most common symptom of colitis?

diarrhea

Intraluminal sequestration of fluid secondary to malabsorptive or hypersecretory mechanisms and dysbiosis

Diarrhea

t/f: Acute or chronic diarrhea can present independent of colitis

true

adult horse can loss up to _____ liters/day with severe diarrhea

100

Etiologies of Acute Colitis/Diarrhea in Adult Horses

Infectious

• Salmonellosis*

• Clostridiosis

• Potomac Horse Fever

• Coronavirus

Toxicologic or other

• Antibiotic-associated

• NSAID associated*

• Carbohydrate overload

what are TWO etiologies of acute colitis/diarrhea in adult horses that we can test for?

Salmonellosis

Clostridiosis

What are Etiologies of Chronic Colitis/Diarrhea in Adult Horses

Chronic parasitism

Inflammatory Bowel Disease

Sand enteropathy

Intestinal Neoplasia

Etiologies of Acute Colitis/Diarrhea in Foals

Infectious

• Rotavirus

• Clostridiosis; Salmonellosis

• Sepsis

Parasitic or protozoal

• Cryptosporidium

Toxicologic/other

• Necrotizing enterocolitis

• Perinatal asphyxia-associated

• “Foal heat”

• Nutritional: lactose intolerance, enteral nutrition

• Antimicrobial/NSAID-associated

Etiologies of Chronic Colitis/Diarrhea in Foals

Infectious

• Lawsonia intracellularis

does systemic inflammation impact disease severity?

yes

what is systemic inflammatory response syndrome (SIRS)?

Clinical/pathological manifestation of uncontrolled systemic inflammation

in foals, what does SIRS usually progress to?

Sepsis: SIRS w/ documented systemic bacterial infection (neonatal foals)

what predisposes horses with colitis to SIRS?

Systemic exposure to circulating bacterial endotoxin (endotoxemia) from damaged GIT predisposes horses with colitis to SIRS

t/f: Prevention of endotoxemia and treatment of SIRS are not critical in management of horses with colitis/diarrhea

false! they are!

what is bacterial endotoxin?

how does endotoxin (LPS) cause inflammation?

what are clinical signs of SIRS?

Inflammation

• Fever, tachycardia, tachypnea

Alterations to perfusion

• Hyperemic/discolored mucus membranes (red, “toxic line”)

• Prolonged jugular fill; prolonged CRT

• Cool extremities, poor pulse pressure

Coagulopathy

• Thrombophlebitis, petechiation

Tissue injury (hypoxia, endothelial injury)

• Laminitis (adult horses), renal injury

• Sepsis (foals) – infection manifested elsewhere

  

Clinicopathologic abnormalities with SIRS

Inflammation

• Leukopenia with degenerative left shift & toxic changes to neutrophils OR leukocytosis

Altered perfusion & tissue injury

• Hyperlactatemia, metabolic acidosis

• Azotemia may suggest kidney injury

• Glucose or triglyceride dysregulation

• Foals: hypo or hyperglycemia

Coagulopathy:

• Thrombocytopenia, hypofibrinogenemia

Clinical signs that may accompany acute diarrhea

• Depression, lethargy, anorexia

• Colic: Ileus, intestinal inflammation, abdominal distension

• Prolonged CRT, skin tent, dry MM

  • Dehydration, hypovolemia

• Encephalopathy (rare; adults)

  • hyperammonemia

clinical presentation depends on (1) and (2)

• Clinical status of these patients can change rapidly

severity of colonic and systemic inflammation

severity of fluid and electrolyte loss

describe the Clinicopathologic findings associated with acute diarrhea

• Increased PCV, azotemia, hyperlactatemia

  • Dehydration, hypovolemia

• Electrolyte and protein derangements

• Metabolic acidosis

• Hypoglycemia (neonates)

• Hyperammonemia (rare; only adults)

  • Clostridiosis; ECoV