Diarrhoea in horses and foals

Question 1

Function of colon - adults and foals

Answer 1

ADULT: water reabsorption and microbial digestion (carbohydrate and protein/non-protein nitrogen)
FOAL: large colon not as well developed as in adults so bacterial pipulation less and less important for fluid absorption. Milk diet.

Question 2

Where is the problem causing diarrhoea located in adults vs foals?

Answer 2

Adult - LI only

Foal - LI or SI

Question 3

How to narrow down the list of DDx for equine diarrhoea - 3

Answer 3

• Age of animal?
• Duration of clinical signs?
• History - presence of risk factors?

Question 4

DDx - neonates - commonest (4) and others (5)

Answer 4

COMMONEST: foal heat diarrhoea, viral (esp rotavirus), salmonella, clostridia
OTHERS: necrotising enterocolitis, sepsis, nutritional diarrhoea, parasitic diarrhoea (Strongyloides westeri), gastroduodenal ulceration.

Question 5

DDx - older foals (up to 10-12 months) - commonest (4) and others (7)

Answer 5

COMMONEST: parasitic (strongyloides vulgaris, cyathostomins), proliferative enteropathy (Lawsonia intracellularis), Salmonella, Clostridia

OTHERS: crytosporidiosis, Rhodococcus equi colotis, viral (especially rotavirus), sepsis, nutritional diarrhoea, gastroduodenal ulceration, parasitic (Strongyloides westeri)

Question 6

What is foal heat diarrhoea?

Answer 6

Nothing to do with the mare’s first heat cycle after parturition but an adaptation/change of the foal’s bacterial population in GIT.

Question 7

DDx - adult equine diarrhoea - common (3) and others (9)

Answer 7

COMMON: Salmonellosis and clostridiosis, or often undiagnosed
OTHERS: parasite, antimicrobial-associated, NSAID, sand enteropathy, carbohydrate overload, inflammatory or infiltrative, dietary (abnormal fementation) neoplasia (lymphoma), peritonitis, abdominal absecessation

Question 8

Differentiate acute and chronic diarrhoea

Answer 8

• ACUTE - acute onset, febrile diarrhoea, clinical signs of hypovolaemia, endotoxaemia
• CHRONIC: if more than 2 weeks duration
• The DDx for acute and chronic actually overlap quite a lot (e.g. salmonellosis, parasitism (larval cyathostominosis, strongylosis), NDSAID toxicity, sand enteropathy and carbohydrate overload can all be either acute or chronic).

Question 9

What are ‘risk factors’ for equine diarrhoea - 4

Answer 9

• NSAID treatment
• anthelmintic history?
• antibiotic treatment?
• contact with other horses/foals with diarrhoea?

Question 10

Is it important to make a definitive diagnosis?

Answer 10

Probably not but you should try because:

• contagious +/- zoonosis
• some specific treatments may work better

n.b. always test an equine diarrhoea case for salmonella

Question 11

3 principles of therapy = ?

Answer 11

• address fluid loss
• address inflammation and endotoxaemia
• address specific cause

Question 12

Principles of fluid therapy?

Answer 12

Mild dehydration seen with 5% fluid loss, sever dehydration with 10% fluid loss. For a 500kg racehorse, figures can be the following:
-deficits - 50L
-maintenance - 48L (2-4ml/kg/hr)
-ongoing losses - 50L
TOTAL = 150L. I/V fluids for this can cost £750 a day!

Question 13

What is an endotoxin?

Answer 13

Part of OM of gram - bacteria. Released during cell death or rapid growth. Horse FIT normally has large numbers of gram negative bacteria but the normal mucosal barrier prevents access to circulation. Endotoxaemia is a complicating factor in many GIT diseases.

Question 14

Why worry about endotoxaemia?

Answer 14

Endotoxin within circulation –> interacts with cells (e.g. macrophages) –> initiates systemic inflammation –> clinical signs of endotoxaemia –> CV and GIT dysfunction, shock, organ failure and death

Question 15

Clinical signs - endotoxaemia - 7

Answer 15

• depression
• tachycardia
• tachypnoea
• fever
• colic
• diarrhoea
• hyperaemic ‘toxic’ mucous membranes

Question 16

Diagnosis - endotoxaemia

Answer 16

Clinical signs

Low WBC count, low neutrophil count, immature ‘band’ neutrophils

Question 17

Treatment - endotoxaemia

Answer 17

• prevent movement of endotoxin into the circulation (hard to do)
• neutralise endotoxin before it interacts with inflammatory cells
• prevent synthesis/release/action of inflammatory cells
• Prevent endotoxin-induced cellular activation

Question 18

What drugs can be used in endotoxaemia? 4

Answer 18

Polymixin b (directly binds endotoxin)
Pentoxyfilline - less effective than polymixin b
Flunixin - blocks prostaglandin production
Hyperimmune plasma (USA) - neutralises endotoxin

Question 19

How is endotoxaemia different in foals? - 4

Answer 19

Similar effects as in adult horses but usually associated with bacteriaemia/sepsis (unlike adults).

• Large colon less well developed therefore gram negative population may be smaller?
• Concern of nephrotoxicity (foal kidney less well developed) of certain drugs (polymixin B or flunixin)
• Treatments = plasma or ABs

Question 20

Can you treat diarrhoea at home or do you need to refer? 4

Answer 20

• Most diagnostic tests/treatments don’t require hospitalisation
• Keeping up with fluids may be challenging (volume and frequency required). If a horse/foal can keep up with fluid requirements by drinking then it is probably okay to treat at home.
• best to be over cautious with foals as they can deteriorate very rapidly
• consider possibility of contagious agent? other animals nearby? (isolation facilities can be provided at a hospital)

Question 21

Considerations - foals on fluids

Answer 21

• volumes required aren’t as large a adults so may be possible to give intermittent but frequent boluses OR
• separate mare and foal for continuous fluids but this is labour intesive!