Bladder sediment and bladder stones

Urolithiasis: Bladder sediment, bladder stones, urinary sediment, and more.

Warning! Urine-soaked fur poses an extreme risk of flystrike! Protect your rabbit!

Concrete deposits in the urinary tract are a condition frequently diagnosed in rabbits kept indoors, even though they appear to affect only about 0.3–1.3% of rabbits overall.

A distinction is made between bladder sludge (urinary crystals in the bladder or urine) and urinary stones, which are classified based on their location: kidney stones, ureter stones, bladder stones, or urethral stones. Female rabbits are only affected by bladder stones, whereas male rabbits may also develop urethral stones.

Bladder stones are composed of:

• Calcium carbonate

• Calcium phosphate

• Calcium oxalate

• Rarely, struvite

Symptoms: How does it present?

The symptoms vary depending on the severity of the condition. The following signs may occur with bladder sludge, often presenting as just one symptom:

• Bloody urine (red drops in normal urine; completely red urine is not blood!)

• Difficulty urinating

• Sludge in the urine (sandy deposits in the urine)

• Increased frequency of urination

• Pain during urination

• Incontinence or lack of cleanliness

• Coarse, dull fur

• Weight loss

• (Chronic) bladder infections

• Wet, urine-soaked fur due to bladder infections, sometimes leading to inflamed skin

• Diarrhea

• Reduced general condition, lethargy

• Decreased or ceased food intake in cases of severe pain

• Emergency: Constant straining without urination often indicates a ureter stone. This can lead to a backup into the kidneys, which is life-threatening. Seek emergency veterinary care immediately!

• Rare symptoms include bloating, cramps, and paralysis or movement disorders in the hind legs.

Causes: How Do Bladder Stones and Sludge Develop?

Urinary tract diseases, alongside dental and digestive problems, are among the most common conditions caused or exacerbated by dietary errors. While hereditary factors influence the development of sludge and stones, even rabbits with a strong predisposition to such conditions rarely fall ill if they are kept and fed optimally. If they do, it is often in conjunction with other underlying conditions, such as pain leading to reduced activity levels or infections that stress the urinary tract.

Nearly all diseases of the urinary tract are diet-related. Rabbits have a unique calcium metabolism, absorbing calcium from their food not based on need but in large quantities. This excess calcium is then excreted through the kidneys. If it is not flushed out with ample water (provided by a diet rich in fresh foods) or if kidney function is impaired, the calcium can deposit in the kidneys or bladder, forming sludge or even stones.

Additionally, the formation of these concretions is promoted by the alkaline pH of rabbit urine.

The development of bladder sludge and stones is usually not attributable to a single cause but rather to the interaction of multiple factors:

• Hereditary predisposition

• Dry or improper diet:
  Lack of water intake: Caused by dry feeding (e.g., pellets, hay, dried herbs) or insufficient water availability, such as the use of nipple drinkers (rabbits tend to drink more from bowls than from nipple drinkers).
  Unbalanced diet: Excessive consumption of dry, calcium-rich, or oxalic-acid-rich foods.

• Other Contributing Factors:
  Lack of movement, housing errors: Reduced movement (due to painful conditions or cramped living space) leads to less agitation of sediment before urination, and the rabbit may visit the litter box less frequently.Indoor rabbits are particularly affected, while outdoor rabbits are less likely to develop these issues (due to more movement, exposure to sunlight for vitamin D production, less frequent urination, and higher rates of neutering). Less frequent urination: Neutered rabbits mark less, and indoor rabbits often have fewer litter box options, which can contribute to infrequent urination. Obesity: This leads to less movement and can exacerbate the risk of urinary tract issues. Older age (seniors): Senior rabbits are more prone to these conditions due to general aging factors and reduced physical activity.

• Other Diseases & Infections:
  Any condition leading to reduced movement: Painful conditions such as spondylosis, arthritis, or other joint issues can limit a rabbit’s mobility, which may contribute to urinary tract problems. Urinary tract infections: These can occur, for example, due to poor hygiene or unsanitary living conditions. Other systemic inflammation: Inflammatory conditions in the body can affect overall health and may influence the formation of bladder sludge or stones. Kidney diseases: Diseases such as those caused by the E. Cuniculi parasite, as well as other kidney issues, are significant contributors. Since 80% of calcium is excreted through the kidneys, impaired kidney function can lead to calcium buildup and the formation of sludge or stones.

• Less frequent urination: Neutered rabbits mark less, and indoor rabbits often have fewer litter box options, which can result in infrequent urination, increasing the likelihood of sludge or stone formation.

• Vitamin D deficiency: Rabbits kept indoors are at higher risk of vitamin D deficiency, as glass windows block UVB rays necessary for vitamin D synthesis. This deficiency can contribute to calcium metabolism imbalances, promoting the development of urinary tract issues.

„Triggering causes, aside from the excess calcium, are primarily improper feeding, lack of exercise, and insufficient water intake. Because improper feeding often coincides with obesity and lack of movement, the term ‚fat lazy rabbit syndrome‘ has emerged, which describes the development of urinary tract diseases in overweight and sedentary animals.“

— Dr. med. vet. Stefan Gabriel

Rabbits are herbivores that naturally feed almost exclusively on fresh plants, which consist of about 80% water. This water is automatically ingested along with the plants. Feeding trials have shown that rabbits consume significantly more water when their primary diet consists of fresh food and they have access to water freely, compared to when they are fed a largely dry diet with free access to drinking water.

The water they consume has a strong diluting effect, meaning that even with high calcium intake, a high water intake can keep the calcium concentration in the urine and urinary tract low. In contrast, if calcium intake is high and water intake is insufficient due to a lack of fresh food, the calcium concentration in the urine rises, leading to the formation of sludge (bladder grit). Over time, this can lead to stone formation. A fresh-food-based diet helps flush and excrete calcium from the organs efficiently. The more calcium is consumed relative to water intake, the higher the likelihood of deposits forming.

„With limited water intake and simultaneously high calcium intake, the risk of urinary stone formation increases. However, this risk remains low as long as the urine volume is high enough. The urine volume is directly dependent on the amount of water consumed […]. Increased water intake helps reduce the concentration of waste substances in the urine, which plays an important role in calcium excretion and potential stone formation. In other words, the more water that is consumed, the lower the risk of urinary stones forming.“

— Dr. med. vet. Natalie Dillitzer: Kaninchen; in: Ernährungsberatung in der Kleintierpraxis: Hund, Katze, Reptilien, Meerschweinchen, Kaninchen. Urban&Fischer, 2009

Another factor that promotes urinary tract diseases is a lack of movement, unsanitary living conditions (such as sitting in bedding soaked with feces/urine), obesity, lack of exercise, and the calcium-to-phosphorus ratio in the diet. Additionally, using a nipple drinker instead of offering water in a bowl leads to reduced water intake.

„Feeding juice-based foods significantly increases water intake and thus dilutes the urine. […] A dietary correction from concentrated commercial feed to a bulky, fiber-rich green food ration not only boosts water turnover but also encourages extensive chewing activity and ensures proper wear of the continuously growing teeth. […] Plenty of free-range activity is a very important additional measure against obesity and helps prevent urinary stones by promoting more movement and more frequent urination.“

— Dr. med. vet. St. Gabriel

Many indoor rabbits suffer from vitamin D deficiency, which can also have significant effects. This can be addressed and prevented with a UVB lamp or vitamin D-enriched food (e.g., JR Farm Grainless Herbs available in pet stores). Additionally, metabolic disorders, kidney diseases, and systemic inflammation can be contributing factors. Therefore, it is important to rule out all possibilities when the cause is unclear.

The kidneys are often affected by the E. Cuniculi parasite, which is carried by nearly every second rabbit in Germany. This parasite impairs kidney function and can lead to the formation of sludge and stones. The presence of E. Cuniculi should always be tested in the blood when bladder sludge or stone formation occurs and, if necessary, treated with Panacur. Even well-nourished and well-cared-for rabbits can develop urinary sludge due to this infection.

„Significantly less water was consumed from the nipple drinker compared to open bowls. Water should always be available ad libitum to prevent compensatory mechanisms, especially in the kidneys, from being activated (TSCHUDIN 2010). These mechanisms reduce water intake, which can lead to urolithiasis in the long term, especially when there are high calcium levels in the diet (KAMPHUES 1991). This is particularly important to consider when providing calcium in excess of the rabbit’s needs (FEHR 1999a).“

A., K. Korn (2016): Dental and Jaw Changes in Rabbits: Diagnostics, Occurrence, and Heritability.

„When rabbits and guinea pigs are fed almost exclusively with fresh greens as recommended, they ingest a large amount of water through their food. This is the best way to prevent urinary sludge and stones. Animals with urinary sludge or stone problems should not be given any dry food – including hay.“

— Dr. med. vet. Diana Ruf, Source

Diagnosis: How Can It Be Determined?

Urine test strips can detect blood in the urine (though this can also be caused by a bladder infection).

Evaluating Urine Test Strips:

• pH value: In healthy rabbits, a pH of 8-9 is normal. A lowered pH value indicates a bacterial bladder or kidney infection or metabolic disturbance (e.g., ketoacidosis).

• Erythrocytes: Positive results show blood (associated with bladder or uterine diseases), but blood can also be introduced during urine collection (spontaneous urine is free of blood, while expressing the bladder can show 1+ to 4+; cystocentesis and catheterization usually show 1+).

• Protein: Normally negative in healthy rabbits. A positive result could indicate a range of underlying conditions, including urinary tract issues, kidney diseases, heart conditions (including thymoma), shock, etc.

• Nitrite: Negative in healthy rabbits. A positive result suggests urinary tract diseases, though false positives can occur due to contamination (bacteria) or nitrate-rich food.

• Bilirubin: Negative in healthy rabbits. Positive values often indicate liver coccidiosis.
  Leukocytes: Not significant in rabbits.

Urine Examination Methods:

• Microscopic Urine Analysis: Used to determine the type of urinary stone and to identify signs of inflammation. Non-radiopaque stones are also visible under the microscope.

• X-ray Imaging: A reliable diagnostic tool for detecting sludge and stones. X-rays should be taken from multiple angles, as some urinary stones may not be visible from just one position.

• Ultrasound Examination: Used to detect urinary issues, including sludge and stones, and to assess the kidneys and bladder.

• Blood Test: Particularly for kidney values and the E. Cuniculi titer (to rule out or treat kidney dysfunction as a potential cause of urinary sludge).

Acidifying the urine, for example with vitamin C, does not work against bladder sludge and stones in rabbits!

Treatment: How is it treated?

• Bladder sludge is flushed out by the veterinarian through bladder lavage (swishing or massaging to loosen the sludge, infusions, and subsequent emptying of the bladder, but caution is needed, as improper handling can cause bladder rupture).

• Depending on the healing process, the veterinarian may demonstrate how to perform this procedure at home, so that it can be done daily. The bladder is shaken and then flushed out with infusions to remove the debris. Bladder expression is generally not performed by the owner but only by the vet.

• At the same time, an antibiotic (e.g., Baytril) is used to treat bladder inflammation. In cases of chronic bladder infections, Angocin is a good option (wash off the protective coating so it can be ingested, or grind it and administer it).

• Painkillers (e.g., Metacam) are very important for managing chronic pain, as the animal may become less mobile and, consequently, worsen or not eliminate the sludge.

• Very small bladder stones can be treated like urine sludge, but larger bladder stones require surgical removal since they would otherwise block the urethra. The stone can be tested for its composition.

• To achieve long-term success, dietary changes are essential. The diet should consist of mostly fresh food, with at least 70% leafy greens and no more than 30% non-leafy vegetables. All dry foods (dry herbs, dry food, hay) contain a very high calcium concentration with low water content, leading to elevated calcium levels in the urine, causing the calcium to precipitate and form sludge.

• Herb-rich hay is unsuitable; ideal hay is Timothy hay.

• The fresh food should not be dried after washing, as this increases water intake. Regularly spray fresh food with a clean flower sprayer or submerge it in water before feeding.

• Water intake can be increased by offering diluted fruit and vegetable juices (without added sugars) in addition to water. Dandelion juice (from a health food store) can also be helpful. Many animals also voluntarily drink kidney and bladder tea.

• Water should be offered in a bowl or bird bowl (hung on a wire), not from a nipple drinker (which leads to reduced water intake).

• Supportive treatments such as RodiCare Uro (alfavet), Uroplex, and Urologist can be administered. These generally help flush the bladder more effectively by having a diuretic effect.

• Many herbs are also diuretic (e.g., nettle, mint, parsley, horsetail, birch, dandelion…) and can serve as an effective alternative to the above-mentioned products when given fresh daily.

• In some animals (though not all), Eurologist and Lysium for bladder stones have led to very good results.

• It may also help to properly „mix“ the bladder so that the sludge does not settle at the bottom but is stirred up and excreted. This can be done by swishing the rabbit („swish grip“ – ask the vet to demonstrate) or tapping the bladder (while the rabbit is normally sitting, gently tap the bladder area to stir up the sludge) and increasing food intake (field hay) or hanging it on ropes.

• Additionally, regular gentle bladder massages can help stir up the sludge.

• More movement also helps mix the bladder contents: Provide your rabbit with a large enclosure and plenty of exercise and variety. Rearranging the items in the enclosure regularly is also beneficial.

• If your rabbit remains relatively inactive, the cause should be identified. Often, single housing, insufficient space, or pain (due to other conditions such as ear infections, joint diseases, uterine issues, or adhesions from abdominal surgeries) is the cause. In these cases, extensive diagnostics may be required by the veterinarian!

• In cases of obesity, weight loss is strongly recommended!

• In indoor housing, ensure sufficient vitamin D supply (without vitamin supplements) via UVB lamps or direct daylight (without window glass).

• If a bladder infection is present concurrently, this can create a vicious cycle, so it should be treated intensively at the same time!

• If E. Cuniculi (EC) is detected, Panacur should be administered as a course in addition to infusions, as EC can impair kidney function.

• If bladder sludge is untreated or treated insufficiently, the bladder will quickly become overstretched, resulting in chronic issues. Therefore, it is crucial to implement a thorough approach from the beginning, including proper diet, veterinary treatment, care, and housing, to prevent an overstretched bladder with chronic bladder problems.

• In severe cases, the bladder may already be overstretched, and it may never fully empty, leading to persistent bladder sludge. In such cases, intensive long-term treatment is necessary (the vet will demonstrate how to stir the sludge in the bladder and administer infusions, see above). Healing is no longer possible at this stage!

• If bladder emptying is impaired, specific medications may help (e.g., bethanechol 1.25–5mg/kg body weight, 3x daily).

• If regular treatment does not work, diuretic treatment, such as Hydrochlorothiazide at a dose of 1mg/kg once or twice daily over 23–25 months, preferably accompanied by infusions, can be used as a last resort after urinary stone surgery.

• In very severe cases, adding salt can increase water intake (0.5g NaCl/kg body weight), for example, on a piece of cucumber (not in the drinking water!).

• As a final option, magnesium L-hydrogenasphartane can be administered at 20mg/kg/day for specific cases.

• For elevated kidney values: See kidney insufficiency.

Example of bladder stone surgery
Photos: Saskia Hintze

Diet and Care for Bladder Diseases

Keep in mind: Only by addressing the underlying cause of the disease in the long term can you cure and prevent urinary tract diseases. Medications alone will result in recurring bladder sludge and similar issues for your animals!

• Increase water intake: When dealing with bladder stones or sludge, it is especially important that rabbits consume a lot of water during treatment and for years afterward, as this helps flush the organs and expel calcium, preventing it from accumulating. Therefore, rabbits should have access to fresh, varied food ad libitum (in unlimited quantities, around the clock), as this provides the most water. Rabbits affected by or prone to such conditions should be fed a diverse diet of fresh food (preferably with meadow herbs in summer, and leafy vegetables and herbs in winter). It is also important to offer water in a clean bowl at all times (water intake is noticeably lower from nipple drinkers). To increase water intake, in addition to fresh food and regular water, diluted carrot juice, vegetable juice, or fruit juice can be offered. Pure herbal tea (if liked) is also beneficial. A medical kidney and bladder tea, such as HEUMANN Bladder and Kidney Tea SOLUBITRAT®, is a good option. These drinks should always be offered in addition to water, not as a substitute.

• Good Calcium-Phosphorus Ratio: Ensure a balanced calcium-phosphorus ratio in the diet of 1.5-2 : 1 (Ca : P) – this corresponds to a value of 1.5-2, or feed the rabbits exclusively with meadow plants (available day and night) or other fresh greens, without other types of food. Meadow plants, the natural food of rabbits, have an even higher calcium-phosphorus ratio. Make sure that the entire diet maintains this balance. You need to pay particular attention to the calcium-phosphorus ratio if you don’t feed the rabbits only fresh greens but supplement their diet with vegetables and hay, or if, despite a purely meadow-based diet, urinary tract diseases occur (such as a strong predisposition to sludge and stones). If the phosphorus content in the food is too high, calcium will be broken down from the body to compensate, which can result in calcium being pulled from the teeth and bones. Conversely, if the phosphorus content is too low, calcium will not be properly incorporated into bones and teeth. If the calcium content of the diet is too high, stones and sludge can form. However, it is absolutely not advisable to reduce calcium (calcium-reduced diet), even though it is often recommended, because this leads to calcium deficiency, which in turn causes urinary stones and sludge, as well as soft bones and brittle teeth. Greens with a less optimal calcium-phosphorus ratio can be included in the daily green mix, but the mix should primarily consist of greens with a good calcium-phosphorus ratio. Hay should be offered in addition, but ideally, there should be enough fresh greens available that the rabbits eat little hay. Avoid using very herb-rich hay. Dried herbs are taboo for rabbits that tend to develop bladder sludge. If you still wish to use leaves and low-calcium herbs, do so only occasionally and in very small amounts. Seeds, grains, hard bread, chew sticks, snacks/treats, and dry food promote urinary tract diseases and should never be offered. Please do not make the mistake of feeding a calcium-poor diet. Unfortunately, this is still widely recommended, but it is harmful to health and does more harm than good (this does not mean that you should offer large amounts of calcium-rich foods). By increasing water intake, the food naturally becomes „calcium-poor,“ but the necessary calcium can still be absorbed from the diet, so there is no risk of damage to bones or teeth.

• Magnesium is also essential for calcium metabolism and is found in insufficient quantities in vegetables. It should be provided in adequate amounts through kitchen herbs and vegetable greens (e.g., carrot tops, fennel greens, etc.).

• Increased feeding: To help loosen and excrete the grit, it has proven effective to offer fresh food in larger amounts, so that the rabbits need to stretch and ’stand on their hind legs‘ while eating. This can be achieved by elevating the food using feeding racks or hanging it on strings.

• Wet Fresh Food: It can also be beneficial to make the fresh food wet, so the rabbits take in more water. This can be done by moistening it with a flower sprayer.

• Diuretic Herbs: The administration of diuretic herbs can be supportive: e.g., nettles (let them wilt for about an hour so they no longer sting), birch leaves and bark, horsetail (also available as juice), asparagus (if they eat it), real goldenrod or giant goldenrod, dandelion (also available as juice), parsley, parsley root, and lovage.

• Vitamin D Deficiency: Be aware that for house rabbits, ensuring adequate Vitamin D intake is crucial. Most rabbits kept indoors or in dimly lit hutches suffer from a significant deficiency. Window glass blocks UV-B rays, which rabbits need to produce Vitamin D naturally in their bodies. Use enriched food or, even better, a UVB lamp, or provide your rabbits with daily access to direct sunlight for extended periods without glass in between (open windows, balcony access, garden enclosures…).

• Exercise: Rabbits that move a lot and are active rarely suffer from urinary tract diseases. Obesity, lack of movement (due to other health issues), a slow metabolism (due to vitamin deficiencies or dry food), little variety, and limited space (keeping them confined to cages/hutches) promote urinary tract issues. Ensure that your rabbits are lively, move a lot, are curious, and have plenty of space. Very calm rabbits are often sick or incorrectly kept and fed.

„Wild rabbits naturally get a lot of physical activity, eat fresh greens throughout the day, and frequently mark their territory with urine, but never in their burrow.
In contrast, a typical ‚caged inhabitant’s‘ daily routine is vastly different: minimal movement, often improper feeding with calorie-dense and calcium-rich dry food, perhaps even ’supplemented‘ with the offering of a calcium-limestone block. Overweight neutered males often have no reason to move more than from the food dish to the toilet corner. Marking indoors is—if free roam is even provided—not desirable and is prevented by neutering. The minimal physical activity leads to the formation of small amounts of highly concentrated urine, which is rarely passed, promoting the precipitation of crystals in the bladder.“

Dr. St. Gabriel, veterinarian

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