Chronic Kidney Diseases in Horses: [Signs & Causes of Renal Failure]

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 may 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 kidneys 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: inflammation 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 supportive care, they can be kept comfortable and partake in appropriate exercise.

To monitor the progression of CKD, your vet will recommend taking regular blood samples to measure markers of kidney function. The most common marker used to evaluate changing kidney function is the level of creatinine in the blood.

Early Kidney Disease

Horses with early-stage kidney disease generally have a serum creatinine level below 5 mg/dL. These horses usually have few clinical signs of disease and a good quality of life. ^[1]

The short-term prognosis for these horses is good, so long as they maintain a healthy appetite and body condition. ^[4]

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Advanced Kidney Failure

Unfortunately, horses are not usually diagnosed with chronic renal failure until much of the kidney is already damaged or diseased.

Many signs of kidney disease are not apparent until 65 – 75% of kidney filtration capacity has already been lost. ^[4] These horses will have serum creatinine levels above 5 – 10 mg/dL.

Even a small increase in creatinine indicates a large kidney function loss. As creatinine values exceed 10 mg/dL, the prognosis worsens. ^[1]

Nutritional Support for Horses with Kidney Disease

There are two main focuses for the nutritional management of horses with kidney disease: (1) maintaining adequate body condition; and (2) avoiding excess protein in the diet.

Dietary interventions focus on managing the side effects of chronic renal failure, rather than treating the disease itself.

1. Maintain healthy body condition

Kidney disease’s most common clinical symptoms are a lack of appetite and weight loss.

To manage these symptoms, affected horses should be fed a palatable diet that supplies adequate calories for weight maintenance.

Forage Selection

Ideally, horses with CKD should be fed good-quality grass hay with less than 10-12% crude protein. A hay analysis is recommended to determine the hay’s protein and energy content.

If the horse is reluctant to consume dried hay, turnout on good-quality pasture is recommended. ^[4]

Alfalfa hay or pasture is not the ideal forage source for horses with kidney issues, but it can be used to stimulate appetite if other hays are refused and pasture is not an option.

Feeding Fats

To increase the energy density of the diet, low-protein energy sources such as fats and oils can be used. Fat sources that provide the omega-3 fatty acids DHA and EPA are recommended.

Human patients with kidney disease taking oral DHA/EPA supplements had reduced blood creatinine and proteinuria levels. ^[12][13]

DHA/EPA supplementation also promoted anti-inflammatory benefits in rats with reduced kidney function. ^[14][15]

Fibre & Cereal Grains

Rapidly fermentable fibre sources such as soybean hulls are another safe energy source for horses with kidney disease.

While beet pulp is generally considered a high-energy fibre source, it is high in calcium and should be used prudently in horses with hypercalcemia.

Cereal grains are low in protein and high in energy. Horses can be fed controlled amounts of grains to encourage appetite. However, their feeding rates should be carefully managed to prevent feeding excess starch and sugar in one meal.

2. Provide adequate but not excess protein

When high-protein diets are fed to horses, the extra protein is broken down into nitrogenous waste products. The kidneys are then responsible for clearing out these waste products.

To minimize the workload of the kidneys, horses with chronic kidney disease should be fed a lower-protein diet that produces lower levels of these waste products.

However, the horse still needs adequate protein intake to support normal weight and a healthy immune system.

Good-quality hay can meet most horses’ protein requirements without needing additional protein sources. Feeds such as alfalfa, soybean meal and high-protein complete feeds should be avoided.

BUN to Creatinine Ratio

To ensure that your horse gets the right amount of protein, your veterinarian can monitor the ratio of urea nitrogen and creatinine in their blood. The ideal ratio of blood urea nitrogen (BUN) to creatinine should be between 10:1 and 15:1. ^[4]

A lower BUN ratio indicates insufficient protein intake while a higher ratio indicates the diet is supplying excess protein.

Additional Tips for Feeding CKD Horses

Other considerations for feeding and managing horses with chronic kidney disease include:

• Provide low-calcium feedstuffs to prevent hypercalcemia
• Avoid the use of NSAIDs and other drugs (aminoglycosides, oxytetracycline, bisphosphonates), which might further impair organ function ^[2]
• Fresh, clean water must be provided at all times
• Feed smaller meals more frequently to stimulate appetite and support digestive health
• Vitamin E supplementation may help reduce oxidative damage in the kidneys ^[2][4][16]
• Depending on the horse’s fitness, mild and regular exercise is recommended to stimulate appetite and maintain fitness ^[2]

Electrolytes and Salt

The kidneys are responsible for filtering and excreting electrolytes such as sodium, chloride and potassium.

Chronic kidney disease can interfere with fluid and electrolyte balance in the horse’s body. Consult with your veterinarian and equine nutritionist to decide whether to supplement with electrolytes.

Provide free-choice salt in loose form, but do not directly supplement with salt unless advised to do so by your veterinarian. Feeding salt could increase renal damage. ^[4]

Salt supplementation may be warranted in horses with low sodium and chloride levels in the blood. Sodium bicarbonate can also be added to the diet in horses with metabolic acidosis and low sodium levels. ^[4]

Renal failure prevents the horse from producing concentrated urine to excrete excess sodium and other electrolytes. Increased intake of electrolytes usually results in increased urinary output among affected horses.

When adding sources of electrolytes to the diet, it’s important to ensure that your horse always has access to fresh water.

Frequently Asked Questions

Here are some frequently asked questions about chronic kidney disease in horses:

Summary

Chronic kidney disease can affect horses of any age or breed, but with early detection and appropriate management, many horses can maintain a good quality of life.

• Although any horse can develop kidney disease, renal failure is relatively rare in the equine population.
• Your veterinarian will monitor disease progression through regular blood testing to assess kidney filtration capacity and overall renal function.
• As long as your horse maintains a healthy appetite and body condition, the short-term prognosis is generally good, particularly in early-stage disease.
• Horses diagnosed and managed early may enjoy a good quality of life for several months or even years with appropriate care.
• Dietary management is a key component of care and typically involves feeding a palatable diet with adequate calories while restricting protein and calcium intake.
• Working with an equine nutritionist can help ensure the diet is properly balanced to support kidney function. You can submit your horse’s information online for a free diet evaluation from our qualified nutritionists.