Equine urolithiasis is the formation of urinary calculi otherwise known as (urinary tract stones) in horses. It is an uncommon disease process in horses, despite the alkalinity of horse urine, coupled with the high levels of calcium that are excreted in horse urine. Male horses are more at risk of developing this condition then females, due to the length of their urethra, which impedes passage of calculi. The most common location that uroliths develop in horses is the bladder.

There are two main types of uroliths that occur in horses, that are designated type I and type II.

• Type I uroliths: Type I uroliths are a yellow-greenish color with a spiculated surface, and made up of a variety of hydrated calcium carbonate salts. These are the easiest to break down for removal in surgery. Type I uroliths are the most common uroliths found in horses.
• Type II uroliths: Type II uroliths are white with a smooth surface and composed of calcium carbonate salts along with magnesium and phosphorus (making them harder than type I uroliths). These are less commonly found in horses.

Urinary calculi very in size and occur when the urine becomes supersaturated with salt and minerals, such as calcium oxalate, struvite, uric acid and cystine.

Clinical signs
The main clinical signs observed in horses with urolithiasis are:

• Presence of blood in the urine (hematuria).
• Horse keeps appearing to need to or inclined to evacuate the bowels (tenesmus)
• Frequent, abnormal urination (pollakiuria)
• Loss of bladder control, often presenting as occasional leaking of urine (incontinence)
• Slow, painful urination that is passed drop by drop (stranguria)
• Horse looks uncomfortable or in pain when urinating (dysuria)
• If calculi develops in the kidneys and ureters, horses often also show signs of weight loss and colic signs.

In chronic cases of horses with urolithiasis, they will often develop urine scalding of the hindlegs and perineum.

Treatment
Surgery is usually required for horses with urolithiasis. Currently, laparocystotomy in combination with laparoscopy is the preferred treatment for urolithiasis in male horses. In female horses, manual extraction or lithotripsy techniques performed via the urethra are the currently preferred techniques.