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Urolithiasis is a rare condition in horses that involves the formation of bladder stones within the horse’s urinary tract. These urinary stones or uroliths are hard collections of crystals or mineral deposits, which can lead to various health complications. [1][2][3]

The most common type of urinary stone in horses is calcium carbonate crystals found within the bladder. Bladder infections often trigger the formation of these stones. [1][2][3]

Symptoms of urolithiasis vary based on where the stones form in the urinary tract. Horses may exhibit subtle signs such as weight loss and reduced appetite, or more overt symptoms such as difficulty urinating and the presence of blood in the urine. [1][2][3]

Veterinarians will typically diagnose urinary stones with a physical examination, including rectal palpation. In certain cases, other diagnostic tools may be needed. [2][3]

Urolithiasis is a condition that requires prompt attention and appropriate management to ensure the well-being of the affected horse. The goal of treatment is to eliminate the stones from the urinary tract and prevent recurrence of this condition. [2][3]

Urolithiasis in Horses

Urolithiasis in horses typically results from the accumulation of mineral salts, primarily calcium, in the urinary tract. [1][3]

Bladder stones typically affect horses that are at least 10 years old, but they can also affect younger horses. Male horses, especially geldings, are the most susceptible to developing urinary stones. [5][6]

Some horses can also have uroliths in their kidneys, which are harder to detect. If stones enter the bladder and continue into the narrow tube known as the urethra, they can get stuck and obstruct the normal flow of urine. [2][3]

Urinary blockages are more common in other species of animals. In horses, males, specifically geldings, are more commonly affected by this issue than females. [2]

Usually, there is only one stone present in the urinary tract at a time. However, if a stone has one smooth side and one rough side, it indicates the presence of more than one stone rubbing together. [3]

Risk Factors

Several factors can contribute to the development of urinary tract stones in equines:

  • Diet: An imbalanced diet with excessive levels of certain minerals, particularly calcium and phosphorus, can predispose horses to urolithiasis. Diets that are high in alfalfa hay or legumes may contribute to bladder stone formation.
  • Dehydration: Insufficient water intake can lead to higher mineral concentrations in urine, which increases the risk of stone formation. Horses that do not have access to clean, fresh water are more susceptible to urolithiasis.
  • Age and Gender: Urolithiasis is more commonly seen in male horses, particularly geldings. This is because geldings have narrower urethras, making it easier for the stones to become lodged in the urinary tract.
  • Breed Predisposition: Certain horse breeds, such as Miniature Horses, are presumed to be more prone to urolithiasis due to differences in conformation. However, genetics are not a known risk factor for uroliths in horses. [3]
  • NSAID Use: Prolonged anti-inflammatory (NSAID) administration can lead to kidney damage, which may contribute to the formation of kidney and bladder stones. [2][6]

Types of Bladder Stones

Uroliths in horses can be made of different minerals that form crystals in the urinary tract. These mineral compositions can vary depending on the specific conditions and dietary factors influencing stone formation.

The most common bladder stones in horses are made of calcium carbonate, a combination of calcium and carbonate ions. [1][2] Stones formed from this type of crystal typically have a rough surface and can crumble when touched. [3]

In some cases the bladder fails to completely empty of urine, typically due to neurological disorders. This type is known as “sabulous” urolithiasis, and is characterized by sandy sediment in a distended bladder. [1][3]

In rare cases, stones may be formed of calcium phosphate, which consists of calcium and phosphate ions. These stones are typically grey-white, smooth, and are not easy to break apart. [1]

Stones made of struvite crystals are even less common in horses. These bladder stones are more common in cats and dogs. [2][7]

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Clinical Signs

Recognizing the signs of urolithiasis in horses is crucial for early diagnosis and treatment. Common symptoms include: [1][3][6][8][9]

  • Weight loss
  • Fever
  • Red, bloody urine
  • Straining to urinate
  • Frequent urination
  • Dribbling urine
  • Only passing small amounts of urine
  • Grunting during urination
  • Colic
  • Sweating
  • Restlessness
  • Decreased appetite
  • Anorexia
  • Difficulty passing manure
  • Hindlimb weakness

The severity of clinical signs varies depending on the location of the stones within the urinary tract. Some symptoms may also be more noticeable after exercise or towards the end of the urination. [3][4][9]

Horses that dribble urine can develop skin sores, also called urine scald. [2] Signs associated with urine scald include redness and wetness of the skin around the perineum of females or hindlimbs in males.

Causes of Urinary Stones

Urinary stones form in horses due to a combination of factors related to urinary tract function and mineral balance.

  1. Minerals in Urine: Horses normally excrete large amounts of minerals, such as calcium carbonate, in their urine. When the concentration of minerals in the urine becomes too high, calcium and other minerals can precipitate out of the urine and form tiny crystals. These crystals serve as the initial building blocks for bladder stones. [1][2][3]
  2. Crystal Aggregation: Over time, these tiny crystals can aggregate and stick together to form larger, solid structures within the bladder. This process is facilitated by the presence of organic materials and proteins in the urine, which can act as a matrix for crystal aggregation. [1][2][3]
  3. Inflammatory Cells: Damaged tissue and inflammatory cells in the urinary tract also provide suitable surfaces for crystals to attach to and start forming stones. Urinary tract infections increase the presence of damaged tissue and cells within the urinary tract, raising the risk of urolithiasis. [3][6]
  4. Stone Growth: Once crystals start to grow in the urinary tract, the alkaline (high pH) urine of horses favors the continued formation of these stones. If urine remains in the bladder for too long, there is a higher likelihood of crystals coming into contact with each other, promoting further aggregation. [3]

If stones are not removed from the bladder, they can result in a persistent cycle of urolithiasis. Rough-surfaced stones can damage the bladder tissue, creating new surfaces for additional stone formation. The presence of bacteria in stones may indicate a concurrent bladder infection. [1]

Secondary Conditions

Urolithiasis can pose a significant health risk to horses, potentially causing discomfort, pain, and severe complications if left untreated.

Secondary conditions associated with bladder stones include urinary obstruction, chronic kidney failure and bladder rupture.

Urinary Obstruction

The most common secondary condition associated with urolithiasis is urinary obstruction. This can occur when a stone becomes lodged in the narrow urethra on its way out of the bladder, resulting in a blockage. Stones that become stuck can partially or completely obstruct the flow of urine. [3]

Male horses are at a higher risk