Bit & Bridle

Equine Urolithiasis (Bladder Stones)

Other Names

  • Bladder stones in horses
  • Cystoliths (bladder stones)
  • Nephroliths (kidney stones)
  • Ureteroliths (stones in the ureters)
  • Urethroliths (stones in the urethra)
  • Urinary calculi

What is Equine Urolithiasis?

Equine urolithiasis refers to the formation of mineralised concretions — commonly called stones or calculi — anywhere within the urinary tract, including the kidneys (nephrolithiasis), ureters (ureterolithiasis), urinary bladder (cystolithiasis), or urethra (urethral calculi). The most common and clinically significant form in horses is cystolithiasis — the presence of one or more stones within the urinary bladder.

Unlike in small animals and humans, where urinary stones can be diverse in composition, equine uroliths are predominantly composed of calcium carbonate, reflecting the alkaline nature of horse urine and the high dietary calcium intake typical in horses fed forage. Stones can range from small, gritty, sand-like deposits to large, irregular concretions weighing several kilograms.

Urolithiasis occurs across all breeds and ages but is most commonly diagnosed in middle-aged to older horses and is more frequently reported in males due to the longer, narrower urethra. Geldings and stallions are at greater anatomical risk of urethral obstruction than mares.

Causes

The exact cause of urinary stone formation in horses is not fully understood, but several contributing factors have been identified:

  • Alkaline urine pH: Horses naturally produce alkaline urine, which favours calcium carbonate precipitation and crystal formation
  • High dietary calcium: Horses on calcium-rich diets (particularly those consuming large quantities of alfalfa/lucerne hay) excrete high urinary calcium concentrations, increasing crystallisation risk
  • Reduced water intake: Inadequate water consumption increases urine concentration, raising the likelihood of mineral precipitation
  • Urinary stasis: Incomplete bladder emptying — whether due to neurological dysfunction, urethral conformation, or positioning — allows minerals more time to accumulate
  • Urinary tract infection: Bacterial infection increases urinary pH and alters the chemical environment in ways that can promote stone formation
  • Sabulous cystitis: Accumulation of sandy sediment in the bladder (sabulous material) may act as a nidus around which a calculus forms

Symptoms and Signs

Signs vary depending on the location and size of the calculus and whether obstruction is present:

  • Frequent urination (pollakiuria): The horse postures to urinate more frequently than normal
  • Straining to urinate (stranguria): Visible effort and discomfort during urination
  • Haematuria: Blood in the urine, appearing pink to red. Often most obvious at the end of urination in horses with cystoliths.
  • Dribbling of urine
  • Urinary incontinence
  • Perineal scalding: Skin irritation in the perineal area from chronic urine dribbling
  • Recurrent mild colic: Particularly after exercise, as movement shifts the stone and irritates the bladder wall
  • Abnormal gait: Some horses adopt a wide-based hindlimb stance or appear stilted behind due to discomfort
  • In cases of urethral obstruction: Complete inability to urinate, severe colic, and rapid deterioration — a genuine emergency

Diagnosis

  • History and clinical signs: Dysuria, haematuria, and frequent urination in a horse are sufficient to prompt urinary tract investigation
  • Rectal palpation: In mares and many geldings, a cystolith in the bladder can often be detected by rectal palpation as a firm, moveable mass within the bladder
  • Urethroscopy and cystoscopy: Endoscopic examination of the urethra and bladder allows direct visualisation of stones and assessment of mucosal damage
  • Ultrasonography: Transrectal or transabdominal ultrasound can identify calculi as hyperechoic structures casting acoustic shadows within the bladder
  • Urinalysis: May reveal haematuria, pyuria (white blood cells), crystalluria, and elevated protein
  • Urine culture: To identify concurrent bacterial infection
  • Radiography: Plain abdominal radiographs can detect calculi in foals and small ponies; in adult horses the stones are often too large and the abdomen too deep for standard radiography to be useful

Treatment

Medical management alone is rarely successful for established calculi — stones cannot be dissolved in horses the way they can in cats and dogs. Definitive treatment requires removal of the stone:

  • Urethrotomy: Surgical incision of the urethra under standing sedation (in males) to allow extraction of smaller cystoliths or urethral calculi. Recovery is generally good.
  • Cystotomy (perineal approach or flank approach): Surgical entry into the bladder under general anaesthesia or, in mares, through the perineal region under standing sedation, to remove bladder stones. Mares are generally easier to treat than males due to broader urethral anatomy.
  • Laser lithotripsy: Available at referral centres — an endoscopic laser fragments the stone into smaller pieces that can be flushed from the bladder. Minimally invasive and growing in availability.
  • Urethral dilatation or catheterisation: For urethral obstruction — urgent relief of obstruction is the priority, followed by definitive stone removal
  • Antibiotic therapy: Where concurrent urinary tract infection is identified
  • Increased water intake: Encouraged through provision of fresh water, electrolyte supplementation, and access to saline water alongside fresh water post-operatively to dilute urine and reduce recurrence risk

Prevention

  • Ensure continuous access to clean, fresh water — horses drink more and produce more dilute urine when water is readily available
  • Avoid diets excessively high in calcium — moderate alfalfa/lucerne intake in horses with a history of urolithiasis
  • Regular urinalysis in horses with a history of calculi to detect recurrence early
  • Manage concurrent urinary tract infections promptly
  • Encourage exercise and movement, which promotes normal bladder emptying

Prognosis

Prognosis is generally good following successful surgical removal of a bladder stone in an otherwise healthy horse. Most horses return to full work. Recurrence is possible — reported in up to 20–30% of horses — and requires ongoing dietary and management attention. Horses with concurrent neurological dysfunction affecting bladder emptying have a less favourable long-term prognosis. Urethral obstruction that is not treated promptly carries a serious prognosis due to the risk of bladder rupture and uroperitoneum.

When to Call the Vet

  • Any horse that is straining repeatedly to urinate without producing a normal stream
  • Blood in the urine — particularly if frequent or persistent
  • A horse posturing to urinate frequently but producing little urine — this may indicate urethral obstruction and is an emergency
  • Recurrent colic, particularly if it seems to worsen after exercise
  • Scalding or skin irritation in the perineal area

Frequently Asked Questions

Are bladder stones in horses painful?

Yes. Even when not causing complete obstruction, bladder stones cause irritation of the bladder mucosa, painful urination, and can produce recurrent colic — particularly when movement shifts the stone against the bladder wall. Most horses with undiagnosed bladder stones have been experiencing low-grade discomfort for some time before diagnosis.

Can a horse urinate normally with bladder stones?

In many cases, yes — especially with smaller stones that do not obstruct the bladder neck or urethra. However, urination is typically painful and the horse may strain, dribble, or pass blood-tinged urine. Larger stones or those lodged in the urethra can cause complete obstruction, which is a veterinary emergency.

Why are male horses more at risk of urethral obstruction from urolithiasis?

Geldings and stallions have a longer, narrower, and more tortuous urethra than mares, with an S-shaped flexure (the sigmoid flexure) that creates a natural anatomical narrowing. Stones that pass from the bladder into the urethra can become lodged at this point or at the urethral process at the tip of the penis, causing partial or complete obstruction.

What diet changes help prevent recurrence?

The most evidence-based recommendations include ensuring good water intake (electrolyte supplementation can help), reducing dietary calcium by limiting alfalfa/lucerne and high-calcium hays, and providing a grass hay-based diet with a balanced mineral supplement. Some veterinarians also recommend adding ammonium chloride to the diet to acidify the urine, though this should only be done under veterinary supervision. See relevant discussion in BEVA clinical resources.