Bit & Bridle

Equine Acute Renal Failure (ARF)

Other Names

  • ARF in horses
  • Acute kidney injury (AKI)
  • Renal failure in horses

What is Equine Acute Renal Failure (ARF)?

Equine Acute Renal Failure (ARF), now more precisely termed Acute Kidney Injury (AKI), is a sudden and potentially reversible deterioration in kidney function that results in the accumulation of metabolic waste products, disruption of fluid and electrolyte balance, and in severe cases, complete loss of urine production. Unlike chronic renal failure, which develops gradually over months to years, ARF can develop within hours to days and represents a medical emergency.

The kidneys play a central role in the horse’s physiology — filtering blood, regulating fluid and electrolyte balance, producing urine, and excreting metabolic waste. When kidney function is abruptly compromised, the consequences ripple through nearly every body system. Horses with ARF are often critically unwell, and rapid diagnosis and supportive treatment are essential to prevent irreversible damage or death.

Causes

ARF in horses can be classified by the primary location of the problem:

  • Pre-renal causes (reduced blood supply to the kidneys):
    • Dehydration from prolonged diarrhoea, colic, or insufficient water intake
    • Haemorrhage or shock
    • Cardiovascular failure leading to reduced cardiac output
  • Intrinsic renal causes (damage to the kidney tissue itself):
    • Nephrotoxins — aminoglycoside antibiotics (particularly gentamicin), NSAIDs (phenylbutazone, flunixin), oxalate-containing plants, and heavy metals
    • Pigment nephropathy — haemoglobin or myoglobin from haemolysis or rhabdomyolysis (tying-up) can damage renal tubules
    • Bacterial infections and endotoxaemia
    • Immune-mediated glomerulonephritis
  • Post-renal causes (obstruction to urine flow):
    • Urolithiasis (bladder stones) — relatively uncommon in horses but can cause obstructive uropathy
    • Urethral obstruction

In practice, aminoglycoside nephrotoxicity and dehydration-associated renal injury are among the most commonly encountered causes in equine clinical settings.

Symptoms and Signs

  • Reduced or absent urine production (oliguria or anuria) — though some horses remain polyuric
  • Depression and lethargy
  • Anorexia
  • Oedema — particularly ventral oedema
  • Oral ulceration in advanced cases (uraemia)
  • Tachycardia and signs of dehydration
  • Muscle trembling or weakness
  • Colic-like discomfort
  • Neurological signs in severe uraemia — depression, seizures

Diagnosis

  • Serum biochemistry: Elevated creatinine and blood urea nitrogen (BUN) are the hallmarks of renal failure. Electrolyte abnormalities (particularly hyperkalaemia, hyponatraemia) are common.
  • Urinalysis: Increased specific gravity (dehydration/pre-renal) or inappropriately dilute urine; proteinuria; casts or granular debris indicating tubular damage. Urine dipstick and sediment examination are important components.
  • Urine gamma-glutamyltransferase to creatinine ratio (uGGT:Cr): An early marker of proximal tubular damage.
  • Urinary fractional excretion of electrolytes: Helps differentiate pre-renal from intrinsic renal causes.
  • Renal ultrasonography: Assesses kidney size, architecture, and identifies hydronephrosis or urolithiasis.
  • Renal biopsy: Rarely performed acutely but can provide definitive histopathological diagnosis in uncertain cases.

Treatment

Treatment is primarily supportive, with the goal of maintaining renal perfusion and removing the causative insult:

  • Aggressive intravenous fluid therapy: The cornerstone of treatment. Large volumes of isotonic polyionic fluids (e.g., Hartmann’s solution) are administered to restore and maintain renal blood flow and encourage diuresis.
  • Remove nephrotoxic drugs: Discontinue any aminoglycosides or NSAIDs immediately.
  • Diuretics: Furosemide or mannitol may be used to promote urine output in oliguric cases, though their benefit is debated and they should only be used once hydration is adequately restored.
  • Treat underlying cause: Antimicrobials for bacterial infection; manage haemolysis or rhabdomyolysis; relieve urinary obstruction if present.
  • Nutritional support: Adequate caloric and electrolyte intake, monitoring phosphorus levels and adjusting diet if required.
  • Monitor closely: Serial biochemistry, urine output, and clinical assessment to track response to treatment.

Management of ARF often requires hospitalisation and intensive care. Referral to an equine hospital is advised in moderate to severe cases.

Prevention

  • Ensure horses at risk of dehydration (those with diarrhoea, febrile illness, or heavy exercise in hot weather) have constant access to fresh water and receive appropriate electrolyte supplementation.
  • Use aminoglycoside antibiotics with caution in horses that are dehydrated or already compromised; maintain adequate hydration throughout treatment courses.
  • Monitor renal function (serum creatinine, urinalysis) in horses receiving prolonged NSAID or aminoglycoside therapy.
  • Ensure pastures are free from oxalate-containing plants.
  • Treat conditions predisposing to rhabdomyolysis promptly.

Prognosis

Prognosis for ARF depends on the underlying cause and severity of injury at the time of diagnosis. Pre-renal ARF with prompt fluid therapy carries a good prognosis. Intrinsic renal damage from nephrotoxins varies — mild tubular injury can resolve completely with appropriate treatment, while severe or prolonged damage may result in chronic kidney disease. Horses with anuric ARF, severe electrolyte disturbances, or advanced uraemia carry a guarded to poor prognosis.

When to Call the Vet

Seek urgent veterinary attention if your horse:

  • Has reduced or absent urine production
  • Is severely dehydrated and lethargic
  • Has recently received aminoglycoside antibiotics or high doses of NSAIDs
  • Has had an episode of severe rhabdomyolysis (tying-up) or haemolysis
  • Shows signs of uraemia — oral sores, profound depression, muscle weakness

Frequently Asked Questions

Is acute renal failure the same as chronic kidney disease?

No — ARF (or AKI) is a sudden, potentially reversible event, whereas chronic kidney disease (CKD) develops slowly over time and is generally irreversible. ARF can, however, progress to CKD if renal damage is severe and the horse survives the acute phase.

Can NSAIDs cause kidney failure in horses?

Yes — NSAIDs such as phenylbutazone and flunixin reduce prostaglandin-mediated renal blood flow. In horses that are dehydrated or have compromised cardiovascular function, this can precipitate or exacerbate renal injury. NSAIDs should always be used at the lowest effective dose and for the shortest necessary duration, with adequate hydration maintained.

How do you monitor a horse on aminoglycoside antibiotics?

Regular monitoring of serum creatinine and urinalysis (particularly urine sediment and uGGT:Cr ratio) during treatment is recommended. Therapeutic drug monitoring of gentamicin trough concentrations helps avoid accumulation to nephrotoxic levels. Ensuring adequate hydration throughout the treatment course is essential.

Can a horse return to work after ARF?

Many horses that recover from mild-to-moderate ARF can return to normal activities, provided renal function returns to baseline. Horses with residual chronic kidney disease may require dietary and management adjustments and are unlikely to return to high-intensity competition work.