Diarrhea & Weight Loss

Question 1

List the most common causes of acute diarrhea in adult horses.

Answer 1

Infectious:
Salmonellosis (zoonotic)
Potomac Horse Fever / Neorickettsia risticii / Equine monocytic ehrlichiosis
Clostridium difficile
Lawsonia intracellularis - weakling age foals
Equine coronavirus

Non-infectious:
NSAIDs
Sand
Antibiotics
Hypoxia - strangulation, distention
Grain overload
Cantharadin tox

Unknown > 50% don’t have a definitive diagnosis

Question 2

Describe the most common clin path parameters in a horse with acute diarrhea, and explain why assessment of these parameters is important for management of these horses.

Answer 2

PCV, TPP - dehydration, protein loss
WBC - typically neutropenia with a left shift - any acute enteritis, endotoxemia
Venous blood gases - typically metabolic acidosis with base deficit due to loss of bicarbonate
Electrolytes - sodium/chloride, potassium - monitor loss
BUN/Creatinine - monitor kidney function

Question 3

Understand the pathophysiology and different diagnostic tests between the most common infectious causes of diarrhea in horses:

Salmonellosis
Clostridiosis
Potomac Horse Fever (Neorickettsia risticci)
Equine coronavirus

Answer 3

Salmonellosis (zoonotic)
Path: primarily an invasive organism; denudes mucosa and invades submucosal vessels; protein loss into bowel; typhlitis & colitis; +/- enterotoxin stimulating cAMP to promote secretion of electrolytes; endotoxin
Dx: 5 serial fecal cultures (negative does not rule out); PCR (x3) b/c intermittent shedding

Clostridium pefringens type A or C
Path:
Dx: Toxin assay; part of GI flora so culture questionable for dx

Clostridium difficile
Path:
Dx: Culture and toxin assay

Potomac Horse Fever (Neorickettsia risticci)
Path: infects monocytes, macrophages, enterocytes
Dx: Fecal or whole blood (monocytes) PCR

Equine Coronavirus
Path: RNA virus
Dx: Fecal PCR; shedding persists up to 25 days

Question 4

Propose a treatment plan for a horse with acute, severe diarrhea.

Answer 4

Isolate

Fluid therapy to tx hypovolemia, dehydration, ongoing losses, provide maintenance
Total Fluids = (deficit + ongoing losses + maintenance - shock dose if given)/24 h
deficit = BWkg * % hydration (10% for severe)
OL = total volume in 24 hrs from reflux/diarrhea
M = 50 mL/kg/d * BWkg

DX: PCV/TPP, Fecal samples (PCR/toxins/float) depending on hx

NSAID to decrease inflammation and provide analgesia - low dose flunixin

Analgesics as needed - xylazine/detomadine or butorphanol

Re-evaluate and adjust fluids as needed

Question 5

Outline an approach to diagnosis of a horse with chronic diarrhea with no other clinical signs or significant pathologic abnormalities, and explain how this approach would differ if the horse had concurrent weight loss or decreased serum albumin concentration.

Answer 5

Chronic diarrhea w/o other clinical signs/significant pathologic abnormalities
Diet - high concentrate, low roughage
Chronic salmonellosis - fecal culture
Parasitism - fecal float
NSAID tox - treatment hx
Inflammatory bowel disease - ventral edema, dermatitis, ocular lesions
Neoplasia - rectal exam, blood chemistry
Sand - hx, several fecal samples
Non-inflammatory: green grass pasture
Non-GIT: congestive heart failure, chronic liver disease

Chronic diarrhea with concurrent weight loss
- diet, teeth, parasites

Chronic diarrhea with decreased serum albumin concentration
Low oncotic pressure - edema in ventral abdomen, pectoral area, chin

Question 6

List the three most common causes of weight loss in horses, and explain how to confirm these problems in a patient.

Answer 6

Diet - nutrition hx

Teeth - oral exam; float teeth

Parasites - fecal float; prophylactic deworming

Question 7

Describe a diagnostic plan for a horse with weight loss.

Answer 7

History/Physical exam
Teeth - oral exam
Diet
Parasites - fecal float
CBC/Chem - specific organ involvement