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. 
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. 
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. 
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. 
Signs of Chronic Renal Failure
- Poor performance
- Loss of appetite
- Excessive urination (polyuria)
- Excessive thirst (polydipsia)
- Poor hair coat
- Swelling at the lowest part of the horse’s stomach (ventral edema)
Your veterinarian will diagnose chronic kidney disease in your horse by taking blood and urine samples to assess kidney function.
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: 
- 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)
Your veterinarian will also perform a urine analysis to check for high levels of protein in your horse’s urine (proteinuria). 
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. 
A horse with chronic kidney disease will produce urine with the same concentration as protein-free blood plasma.
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. 
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. 
Since many of the symptoms of CKD are non-specific, it is likely that the actual prevalence is much higher.
Kidneys undergo structural and physiological changes as they age, reducing their glomerular filtration rate (GFR).  Kidneys may accumulate damage over time, making older animals more susceptible to chronic kidney disease. 
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. 
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.
More commonly, CKD disease is seen in horses born with healthy kidneys that developed a kidney disorder later in their lifetime.  This is referred to as an acquired kidney disease.
Congenital Causes of CKD
- 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: 
- 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
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. 
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.  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. 
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.
If the horse is reluctant to consume dried hay, turnout on good-quality pasture is recommended. 
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.
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, 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. 
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 
- Fresh, clean water must be provided at all times
- Feed smaller meals more frequently to stimulate appetite and support digestive health
- Vitamin E supplementation can help reduce oxidative damage in the kidneys 
- Depending on the horse’s fitness, mild and regular exercise is recommended to stimulate appetite and maintain fitness 
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.
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. 
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.
Any horse can develop chronic kidney disease regardless of age or breed. Thankfully, renal failure is relatively rare in horses.
Your veterinarian will monitor the progression of kidney disease through regular blood testing to assess the filtration capacity of the kidneys.
So long as your horse’s appetite and body condition remain healthy, the short-term prognosis is good. A well-managed horse diagnosed with early-stage chronic kidney disease can have a good quality of life for several months or years.
Managing a horse with chronic kidney disease involves feeding a palatable diet with adequate calories and restricted intake of protein and calcium.
Working with an equine nutritionist can help you ensure that your horse’s diet is balanced and optimized to support kidney function. Submit your horse’s information online for a free diet evaluation from our qualified nutritionists.
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