Bladder Sludge and Bladder Stones in Rabbits and Guinea Pigs

Both rabbits and guinea pigs may be affected by diseases of the urinary tract. Often, when rabbits and guinea pigs have disease of the urinary tract, there is a build up of large amounts of crystalline material in the bladder called “bladder sludge”. 

Bladder stones, called urinary calculi, can form when the crystals cement together to form a mineralized, oval-shaped mass inside the bladder.

What are common causes of bladder sludge and bladder stones? 

There are several factors that may contribute to this disease process: eating too many calcium-rich vegetables, underlying bacterial infections of either the kidneys or bladder, Encephalitozoon cuniculi infection, obesity, and genetic predisposition are all factors to consider as underlying causes of bladder sludge or bladder stones. 

Calcium-rich vegetables such as kale, spinach, turnip greens, and collard greens should not be given to rabbits or guinea pigs free choice and should not be given daily. These green leafy vegetables are ok in small quantities but can lead to excess calcium in the bloodstream that then must be filtered by the kidneys and may cause calcium mineral deposits in the urine. 

Bacterial infections of the kidneys or bladder are a common cause of bladder sludge. The bacteria irritate the lining of the urinary tract or bladder, which causes particles of inflammatory products to become starting blocks for minerals to connect to and form either sludge or stones.

Encephalitozoon cuniculi is a microsporidian parasite that may affect several different organs within a rabbit’s body. When this organism causes an infection in a rabbit's kidneys, it may result in bladder sludge formation. 

Obese rabbits are predisposed to bladder sludge due to lack of activity, which causes urine to settle in the bladder and not swirl around like it would in an active, agile rabbit. In addition, overweight rabbits and guinea pigs tend to have fatty tissue around the genital regions that allow bacteria to build up and potentially seep into the opening of the urinary tract and work their way up to the bladder. Obese rabbits and guinea pigs may also have improper posture when urinating, causing incomplete emptying of the bladder and setting the stage for bladder sludge and/or bladder stone formation. 

Some guinea pigs also seem to have recurring bladder stone formation, which suggests that there may be a genetic predisposition for bladder stone formation. 

What are the symptoms of bladder sludge and bladder stones? 

The most common symptoms noted by owners of rabbits and guinea pigs with bladder sludge is that the pet's urine has a very strong smell, its color is darker, and it appears to have sandy-looking material in the liquid. In addition, since the urine is thicker and has crystals in the liquid, urine often dribbles down the inside of the back legs, causing the hair to be matted and stained. In advanced cases, the skin becomes red and ulcerated from urine scald. 

Pets with bladder stones may show few to no symptoms at first. Once the stones become larger, they often cause bloody urine known as hematuria. In cases with extremely large stones, the abdomen may appear swollen. 

Male rabbits and guinea pigs are prone to blockage of the urethra (the distal end of the urinary tract) by tiny stones that are small enough to leave the bladder but too large to pass easily. In these cases, the pet may strain or vocalize when attempting to urinate. This condition is less common in female rabbits and guinea pigs. 

How are bladder sludge and bladder stones diagnosed? 

If you notice any of the above symptoms, it is absolutely necessary to visit a veterinary hospital that is knowledgeable in rabbit and guinea pig disease, as soon as possible. Your veterinarian will perform a thorough physical examination and, in some cases, they may be able to feel a bladder stone or bladder sludge when they palpate (feel) the bladder. A bladder stone feels like a hard, round mass with the consistency of a rock. Bladder sludge feels like the bladder is partially filled with sand, so the contents are gritty and doughy at the same time. 

An X-ray (radiograph) of the abdomen is always necessary. In some cases, there is more than one bladder stone, so it is critical to know that before proceeding with a treatment plan. Bladder sludge appears like part or all of the bladder is filled with a mineral dense material. In advanced cases, mineral deposits may be noted in the kidneys, and this is a sign that the case may have a poor outcome. A complete blood count (CBC) and blood chemistry profile should be performed to assess the presence of infection and to determine if kidney function has been damaged by the disease process. 

How are bladder sludge and bladder stones treated? 

The first order of business is to determine if the kidneys are functioning properly. If there has been substantial damage to kidney function, treatment outcomes become more grave. 

Rabbits with bladder sludge benefit from hospital treatment with subcutaneous or IV fluids to help dilute the urine in the bladder. In severe cases, the rabbit may need to be anesthetized and have a urinary catheter inserted into the urethra and advanced into the bladder to flush out the sludge. The underlying cause needs to be identified and corrected as well. If too many calcium rich vegetables are being fed, they must be eliminated. If the rabbit is E. cuniculi positive, it must be treated. 

Guinea pigs do not commonly get bladder sludge but will benefit from a dietary change and hospital treatment with fluids. 

If bladder stones are identified on X-rays, the only way to resolve the case is by surgical removal of the bladder stones. Abdominal surgery is best accomplished by a surgeon familiar with rabbit and guinea pig surgery. The anesthesia is different than that for dogs and cats, the post-op recovery is different than for dogs and cats, and the bladder is much smaller. Surgical outcomes are very good in most cases. Unlike dogs and cats, there is no “prescription diet” that dissolves the stones. 

In cases of both bladder sludge and bladder stones, your veterinarian may prescribe post-op or post-treatment antibiotics. 

Will the bladder sludge or bladder stones recur? 

If a guinea pig has a bladder stone, it may recur several months later if the guinea pig is genetically predisposed to stone formation. It is critical to change the diet to exclude or greatly diminish green leafy vegetables. 

If a rabbit has a bladder stone, it does not commonly recur once the stone is surgically removed. If the rabbit has an underlying bladder infection, antibiotic therapy will be necessary.