Diarrhoea in horses

Question 1

What are the different mechanisms of diarrhoea?

Answer 1

1. Malabsorption - loss of absorptive cells
2. Increased secretion - active/passive
3. Osmotic overload - feed, maldigestion
4. Abnormal motility - inadequate mixing (stress)

5.Extravasion of fluid (oedema) - hydrostatic, colloid osmotic

Question 2

What part of the intestine is affected with diarrhoea?

Answer 2

*Adults = LI always affected - disease of SI does not cause diarrhoea
*Foals = diarrhoea can occur with SI disease - fluid from SI overloads LI absorptive capacity (Rotavirus / Lawsonia)

Question 3

What does chronic diarrhoea affect?

Answer 3

*All ages + all breeds - rarely life threatening

Question 4

What happens with chronic diarrhoea in adult horses?

Answer 4

*Can progress from acute diarrhoea
*Many conditions of weight loss cause diarrhoea
*Only occurs with extensive colon damage
*Can have colonic pathology without diarrhoea

Question 5

What are differential diagnosis of chronic diarrhoea in adult horses?

Answer 5

• Dietary causes - abnormal fermentation
• Dental disease
• Parasitism e.g. strongylosis
• Sand ingestion
• Antimicrobial associated diarrhoea
• Non-steroidal anti-inflammatory toxicity (right dorsal colitis)
• Non-gastrointestinal causes (kidney, liver, heart)
• Infiltrative disorders (inflammatory bowel disease)
• Neoplasia (e.g. lymphoma)
• Chronic salmonellosis
• Non – intestinal conditions (Liver disease, congestive heart failure, renal disease)

Question 6

What should you find out about the horse’s history?

Answer 6

*management
*Diet + diet changes
*Exercise, travel + other causes of stress
*Deworming + other treatments
*History of recurrent episodes
*Diarrhoea in contact animals

Question 7

What are clinical signs of chronic diarrhoea?

Answer 7

*No / mild dehydration
*Bright + eating well
*+/- weight loss
*+/- polydipsia
*+/- oedema

Question 8

How would you investigate chronic diarrhoea? (tests)

Answer 8

*5 faecal samples for salmonella culture
*Faecal sample - parasites / sand
*Haematology + biochemistry
*Ultrasound
*Rectal / duodenal biopsy
-Diagnosis in <50% cases

Question 9

How is chronic diarrhoea treated?

Answer 9

*Treat underlying cause
*Deworm - fenbendazole / ivermectin
*probiotics
*Anti-diarrhoeal medicines (ineffective long term)

Question 10

Why does inflammation look black on ultrasound?

Answer 10

Oedema - fluid = black

Question 11

What are causes of acute colitis in horses >9months old?

Answer 11

*Idiopathic
*Larval cyathostominosis
*Salmonella
*Clostridium difficile
*Drug-induced = antibiotics / NSAIDs
*Carbohydrate overload
*Sand

Question 12

What are predisposing factors of acute diarrhoea?

Answer 12

*Antibiotic Tx - alters GI flora
*NSAIDs
*Transport
*Competition
*Hospitalisation
*Surgery
*ANY STRESS

Question 13

What is endotoxaemia also known as in horses?

Answer 13

*Systemic Inflammatory Response Syndrome
‘SIRS’

Question 14

What are presenting signs of SIRS?

Answer 14

*Depression
*Fever
*Tachypnoea / Tachycardia
*Purple MMs
*Slow CRT >2s
*Anorexia
*Dehydration
*Reduced GI sounds
*Colic
*Diarrhoea

Question 15

What is the pathophysiology of acute diarrhoea?

Answer 15

*GI mucosal inflammation, ischaemia + reperfusion injury
*Breakdown of GI mucosal barrier = absorption of endo/exotoxins
*Fluid loss - malabsorption, excess secretion + loss of Na

Question 16

How does SIRS occur?

Answer 16

1.Toxins = inflame colon
2.Enter hepatic portal vein
3.Overwhelm clearance mechanism of liver
4. Enter systemic circulation
5. SIRS

Question 17

What does systemic toxins cause?

Answer 17

*Fever
*Inflammation
*DIC + haemorrhage
*Oedema
Shock
**Multi organ failure

Question 18

What is the relevance of SIRS damaging extracellular matrix of laminae of the hoof?

Answer 18

Causes laminitis

Question 19

What is the most common salmonella causing diarrhoea in horses? What are sources of infection?

Answer 19

*S. typhimurium
*Asymptomatic shedders / diseased horses
*Environmental factors - stressors (Transport, hospital, GI surgery, antibiotics)

Question 20

How is salmonellosis diagnosed?

Answer 20

*Faecal culture

Question 21

How is salmonella spread reduced?

Answer 21

*Isolation
*Disinfection

Question 22

How is antibiotic induced diarrhoea treated?

Answer 22

*Withdraw antibiotics
*Supportive Tx

Question 23

How is fluid therapy carried out?

Answer 23

*Determine dehydration + ongoing losses + maintenance = administer fluids
*Boluses of isotonic crystalloids
*Severe hypovolaemia = hypertonic saline rapidly

Question 24

What are other supportive therapies?

Answer 24

*Treat SIRS = NSAIDs, Ice feet against laminitis
*Misoprostol
*Antibiotics
*Oral protectants