A synonym for "kidney" is the word "renal" and is frequently the term used in medical jargon. So when you see the word "renal", think kidney. Before starting, it is important to understand the difference between renal disease and renal failure. Because of the large reserve of kidney function the kidneys can be diseased without failing and if the disease does not have other symptoms the disease may go unnoticed until it progresses to the point of kidney failure when about 2/3rds to 3/4ths of the kidney are not functioning.

Acute renal failure means a disease with a rapid onset that effects the kidney to the point where most of the kidney is not functioning and therefore the kidney cannot keep the blood free of toxins, balance fluids and electrolytes. Acute renal failure is a rare but serious disease in the horse, with the possible exception of bladder rupture in neonatal male foals. This article discusses causes of renal failure, symptoms, causes, diagnosis, treatment, and prognosis.

As discussed earlier it is always important to remember the kidneys can be diseased without failing. Until they fail there will be no symptoms directly attributable to the diseased kidney. Acute renal disease and failure is frequently a secondary condition to some other "primary disease" so the predominant symptoms present may be that of the primary disease. Acute renal disease should be suspected in those diseases known to harm the kidneys, particularly if the horse's clinical signs are worse than expected with the primary disease. Signs of the kidneys failing are due to the build up of toxins in the blood, water imbalances, and electrolyte imbalances and include:

• No or dimished urine output (acute severe insult to the kidndys)
• Excessive urine output is also possible with kidney disease. This is more common in chronic renal failure since the loss of ability to concentrate occurs before the lost of ability to remove toxins and balance electrolytes...more.
• Depression
• Loss of appetite
• Weakness

If the toxin levels become very high severe neurological signs will be exhibited: head pressing, mania, and coma may develop. Other correlating signs of ARF are dehydration, elevated heart rate, red mucous membranes, fever, colic, and laminitis. Renal failure is easily diagnosed in most cases with urinalysis and blood work, see diagnosis below.