Urolithiasis in Horses: Urinary Stones, Straining, and Blood in Urine

Urolithiasis is the formation of urinary stones, also called uroliths or calculi, in the horse's urinary tract. These stones most often develop in the bladder, but they can also occur in the urethra, ureters, or kidneys. In horses, the most common stone type is calcium carbonate, which fits with the naturally alkaline, mineral-rich urine horses produce.

Some horses show subtle signs at first. A pet parent may notice blood in the urine after exercise, repeated posturing to urinate, dribbling, or mild colic-like behavior. Others become much more uncomfortable if a stone irritates the bladder lining or blocks urine flow.

Although urinary stones are considered relatively uncommon in horses, they matter because they can cause pain, inflammation, infection, urine retention, and in severe cases kidney damage. The good news is that many horses do well once the stone is identified and removed, especially before a complete obstruction develops.

Urinary stones form when minerals collect around an organic core and gradually build into a solid mass. Horses are somewhat predisposed because their urine normally contains mucoprotein, is usually alkaline, and often carries calcium carbonate crystals. That combination can make it easier for minerals to stick together over time.

Most equine stones are made of calcium carbonate, though calcium phosphate, struvite, and sabulous stones can also occur. Stones may stay in the bladder, move into the urethra and obstruct urine flow, or less commonly form in the kidneys and then affect the ureters.

Risk does not come from one single cause in every horse. Older horses are affected more often, and males, especially geldings, are overrepresented. Diet may also matter. High-calcium feeds such as alfalfa and other legumes may contribute in some horses, particularly when paired with urine chemistry that favors stone formation. Your vet may also consider whether prior urinary tract inflammation, incomplete bladder emptying, or kidney changes played a role.

In some cases, long-term NSAID-related renal papillary injury may predispose a horse to kidney or ureteral stones. That does not mean NSAIDs should never be used. It means medication history is one more piece of the puzzle your vet may review.

Diagnosis starts with a careful history and physical exam. Your vet will want to know when the urinary changes started, whether blood in the urine happens after exercise, how much urine your horse is producing, and whether there are signs of colic, dribbling, or urine scalding. In some horses, a bladder stone can be felt on rectal exam, and an obstructed bladder may feel enlarged.

Ultrasound is one of the most useful tests for confirming a stone in the urinary tract. Depending on where the stone is located, your vet may also pass a urinary catheter to check urethral patency or use endoscopy to directly visualize a urethral or bladder stone. Kidney and ureter stones are usually assessed with ultrasound as well.

Urinalysis and bloodwork help your vet look for blood, inflammation, infection, and kidney involvement. If a stone is removed, urine culture and stone analysis are especially helpful because they can guide prevention planning and help your vet decide whether diet or other management changes make sense for your horse.

Because blood in the urine can also be caused by cystitis, kidney disease, trauma, or other urinary problems, diagnosis should not stop at the symptom alone. The goal is to identify the stone's location, whether there is obstruction, and whether the kidneys are also affected.

Prevention focuses on lowering the conditions that allow stones to form again. That usually means reviewing the whole picture with your vet: diet, forage type, mineral intake, water source, exercise level, and whether your horse has had previous urinary tract disease. If a stone was removed, stone analysis is one of the most useful tools because prevention works best when it matches the stone's mineral makeup.

For many horses, your vet may recommend reducing high-calcium feeds such as alfalfa and other legumes, especially if the stone contains calcium. Balanced nutrition matters more than one ingredient alone, so feed changes should be made thoughtfully rather than by guesswork.

Good hydration also matters. Horses that drink well generally flush the urinary tract more effectively. Clean, palatable water, routine dental care, sensible salt use when appropriate, and management that supports regular drinking can all be part of a prevention plan.

Urinary acidification is sometimes discussed, but it is not easy to maintain in horses on hay diets, and long-term acidifying salts can have downsides. That is why prevention should be individualized with your vet instead of copied from another horse's plan. Recheck exams, urinalysis, and follow-up ultrasound may be recommended for horses with a history of stones.