Equestrian Days - Kidney Failure in Horses

From Your First Horse to Your First Foal

In many cases, renal failure is identified while a horse is receiving treatment for another illness, such as colic or diarrhea, that reduces blood pressure or otherwise distresses the function of all of the internal organs. When blood pressure drops or the body's vital support systems are stressed, the kidneys cannot remove nitrogen and other waste products from the blood; nor can they maintain adequate levels and balances of water and electrolytes. Kidney disease also occurs when the organ is damaged. Conditions and substances that can harm the kidneys include:

Dehydration due to diarrhea, excessive sweating or simply a lack of sufficient water to drink. As the body's fluid level declines so does blood pressure. The kidneys lose the driving pressure necessary to separate water from the blood solids. Kidney damage can occur within hours of the initial stage of dehydration.
Heatstroke, which has the same effect on the kidneys as dehydration. Marked by a cessation of sweating and an extremely high body temperature, heatstroke often results from physical exertion. During strenuous exercise, blood flow is deflected from the kidneys to serve the hardworking muscles. During ensuing heat stroke, blood is deflected to the skin and lungs.
Natural toxins found in certain plants, such as wild and cultivated onions, bracken fern, white snakeroot and withered red maple leaves. The toxic substances damage the cells that retrieve or reject the constituents routed through the kidneys. When the cells are disabled, the loop of Henle cannot distinguish what to absorb or excrete. As a result, wastes remain in the body or are washed out with valuable substances in a flood of unsorted blood fluids. Just a few ounces of leaves or root are enough to cause serious illness, but cases of such poisoning are rare since most horses will avoid these plants if they have other grasses to eat.
Aminoglycoside antibiotics, nonsteroidal anti-inflammatory drugs (NSAIDs), vitamin D and vitamin K. Usually beneficial to horses, these substances are toxic in high doses, but incidents of such poisoning are rare. Dangerously high doses of vitamins D and K are possible only through injection.
Mercury. Highly toxic to horses, mercury was once used as a skin-blistering agent, and horses would ingest it by licking it off of their inflamed legs. The substance is no longer routinely used, so horses have little opportunity to come into contact with it.
Massive blood loss from a serious wound or other injury that causes an immediate and drastic drop in blood pressure, which, in turn, diverts critical blood flow from the kidneys.
Shock, which depresses blood flow to the kidneys, slowing the filtration process.
Colic, which stresses all of the body's vital organs and can result in the formation of clots in the blood. These clots may clog the kidneys, trapping toxins in the body.
Bacterial infection, which can damage the kidney cells. The resultant inflammation may affect the tubules to the point where plasma water can no longer pass through.
Chronic urinary obstruction, which can damage the kidneys over time, but is very rare; a kidney stone or tumor can block urination without damaging the organs.

Diagnosis and treatment

The kidneys' obscure position within the body makes it difficult to view them with X-rays, ultrasound or an endoscope, but testing their condition is relatively easy. By taking a blood sample and a urine sample at the same time, a veterinarian can compare the levels of creatinine (a muscle-energy waste product), electrolytes and enzymes. An excessive amount of waste products in the blood or nutrients in the urine may point to irregular kidney activity. Elevated creatinine levels do not occur until 70 percent of the nephrons in both kidneys are severely damaged. The range of a normal creatinine level is less than 1.8 to 2.0 mg/dL. Severe kidney dysfunction is marked by levels as high as 15 or 20 mg/dL.

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"If we can maintain it at a level that is less than 5.0, the horse may do well for several years," Schott says. "When it starts to get above 5.0, and we can't get it lower, that is usually an indication that the horse has only a few months to live."

The blood test of a horse with some degree of kidney dysfunction may also reveal signs of anemia, due to the destruction of red blood cells. Excess calcium may also appear in blood samples if the kidneys are unable to excrete the mineral.

Recovery from the condition generally depends on the underlying cause, the length of time the kidneys have suffered and the horse's response to treatment. At all stages of kidney disease the goal of treatment is to lighten the kidney's workload. In the case of acute renal failure, the first order of business is to treat the cause whether it's colic, shock or dehydration. Chronic renal failure, however, creeps up over months or years at a time, without detection, and is extremely difficult to treat.

Surgery is rarely performed due to the difficulty in reaching the kidney through the ribs and diaphragm. It is attempted only in cases of extreme cases, such as cancer, and on only one kidney.

The most important step in improving kidney condition is to replenish fluids, and some affected horses may require the administration of intravenous fluids. Any horse with kidney damage needs an unlimited supply of fresh water, as well as access to salt and electrolytes. If the horse shows signs of anemia or insufficient production of red blood cells, vitamin B complex and anabolic steroids may help boost cell production and prevent muscles from wasting away.

Since reducing stress on the kidneys is paramount, supplying an easily digested diet with low protein and low starch will help to ward off further damage. Replace grain with a soluble fiber, such as bran, beet pulp or low-protein corn. Steer clear of stemmy, coarse hays like alfalfa and clover, which tax the digestive system. For roughage, try a grass hay, such as timothy, which is low in calcium.

Studies show that horses who are able to eat well and overcome the weight loss associated with kidney disease have a better chance of recovering. With nutritional changes and a well-planned exercise schedule, a horse can continue performing despite a kidney disorder.

Perhaps if they were less resilient and whole lot less dependable, your horse's kidneys might capture a bit more of your attention. As it stands, they work without notice or recognition--and we're grateful: That's the way it should be.

This article originally appeared in EQUUS Magazine in March 2000