Chronic kidney disease (or chronic renal failure) in horses is a rare but serious disorder that interferes with normal kidney function.

Your horse’s kidneys perform many important processes in the body including managing blood pressure, excreting waste products, and regulating electrolyte balance.

When kidney function is impaired, waste products begin to build up in the blood and affect the function of other organ systems.

Horses with reduced renal function often experience weight loss and have difficulty maintaining body condition. They may also show signs of poor coat quality, excessive thirst and increased urination.

Chronic kidney disease is incurable, but if it is caught early the progression of the disease may be slowed. Horses with renal failure benefit from nutritional interventions to reduce strain on their kidneys.

Chronic Kidney Failure in Horses

Chronic Kidney Disease (CKD) is a progressive and irreversible disease of the kidney that is characterized by reduced renal function. [1]

As a progressive condition, the kidneys experience a gradual decline in renal function over a period of months or years. This loss in function must persist for at least three months to be considered chronic. [2]

Functional loss is defined as a reduction in the glomerular filtration rate, which measures how well the kidney remove waste and fluid from the blood.

Loss of Kidney Function

Reduction in the filtration rate prevents the kidney from performing its normal jobs which include:

  • Regulating water and electrolyte balance
  • Regulation of blood pressure
  • Maintaining normal blood pH
  • Excretion of waste products
  • Production and elimination of hormones

As kidney function declines, waste products that are normally excreted in the urine can build up in the blood. [1]

The build-up of waste products in the blood can negatively impact the function of other cells and tissues, leading to the development of other disorders such as uremia or multiple organ dysfunction. [1]

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Signs of Chronic Renal Failure

The most common sign of chronic renal failure in horses is weight loss. [1] Other common symptoms include: [3][17]

  • Poor performance
  • Loss of appetite
  • Excessive urination (polyuria)
  • Excessive thirst (polydipsia)
  • Dehydration
  • Poor hair coat
  • Swelling at the lowest part of the horse’s stomach (ventral edema)
  • Colic

Diagnosis

Your veterinarian will diagnose chronic kidney disease in your horse by taking blood and urine samples to assess kidney function.

Blood Tests

Your veterinarian will order a serum chemistry profile to look at levels of several nutrients and metabolites in the blood.

A blood test from a horse with kidney disease will likely show one or more of the following abnormalities: [3]

  • Azotemia (abnormally high level of nitrogen waste – creatinine – products in the blood)
  • Hyponatremia (low levels of blood sodium)
  • Hypochloremia (low levels of blood chloride)
  • Hypophosphatemia (low levels of blood phosphorous)
  • Hypoproteinemia (low levels of blood protein)
  • Hyperkalemia (elevated blood potassium)
  • Hypercalcemia (elevated blood calcium)
  • Metabolic acidosis (excessive acidity in the body)

Urine Tests

Your veterinarian will also perform a urine analysis to check for high levels of protein in your horse’s urine (proteinuria). [3]

They will also look for indicators of isothenuria, which occurs when the kidneys are unable to make concentrated or dilute urine. This can indicate damage to other structures of the kidney such as the tubules. [3]

A horse with chronic kidney disease will produce urine with the same concentration as protein-free blood plasma.

Additional Tests

Your veterinarian will likely perform an ultrasound, rectal exam or renal biopsy to determine if there is any damage in the kidney’s tissues or structures.

Chronic kidney disease is most commonly diagnosed in horses with chronic weight loss and positive results for azotemia and isothenuria. [4]

Prevalence and Risk Factors

A study looking at 32 years of medical records between 1964 to 1996 found that only 0.12% of horses in a medical database were diagnosed with chronic kidney disease. [3]

Since many of the symptoms of CKD are non-specific, it is likely that the actual prevalence is much higher.

Any horse, regardless of age or breed, can develop kidney diseases. However, older horses are more susceptible to developing CKD. [1]

Higher rates of kidney disease are seen in older animals of many species, such as cats, dogs and humans. [5][6]

Kidneys undergo structural and physiological changes as they age, reducing their glomerular filtration rate (GFR). [7] Kidneys may accumulate damage over time, making older animals more susceptible to chronic kidney disease. [2]

One study found that stallions and Thoroughbreds were more likely to be diagnosed with CKD. However, the author also noted that these animals might have been over-represented due to their higher degree of veterinary care in these groups of animals. [3]

Causes of Equine Kidney Disease

Chronic kidney disease can be caused by structural abnormalities in the kidneys or a disease that is present at birth. These are described as congenital kidney diseases.

When a horse under 5 years of age is diagnosed with CKD, it is usually caused by congenital diseases. [4][8][9]

More commonly, CKD disease is seen in horses born with healthy kidneys that developed a kidney disorder later in their lifetime. [10] This is referred to as an acquired kidney disease.

Some horses that present with kidney failure might have both a congenital and an acquired kidney disorder. [9][12]

Congenital Causes of CKD

The congenital causes of kidney disease include: [3][11]

  • Renal dysplasia: malformed kidneys that are not properly developed before birth
  • Polycystic kidney disease: an inherited disorder that causes fluid-filled cysts to grow in the kidneys
  • Renal hypoplasia: when one or both kidneys are abnormally small
  • Renal agenesis: when one or both of the kidneys fail to develop

Acquired Causes of CKD

The acquired causes of chronic renal failure include: [3]

  • Chronic interstitial nephritis: a swelling in between the kidney tubules
  • Glomerulonephritis: inflammation of the glomeruli, tiny blood vessels that act as filters in the kidneys
  • Untreated or recurring acute kidney failure: also known as acute kidney injury, which is a sudden loss of kidney function
  • End-stage kidney disease: a general term to describe a severe case of kidney failure where the signs are too advanced to be able to determine the primary cause

Prognosis

Chronic kidney disease is irreversible and progressive, meaning that horses affected by CKD have no chance of recovery.

However, early interventions may slow the rate of progression and increase longevity and quality of life in the affected horse.

If chronic renal failure is diagnosed early and the horse is given