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Hypercalciuria and Bladder Sludge in Rabbits, From Diet to Cystotomy

PublishedOctober 16, 2026Reading time7 minExoticRx Editorial

Editorially reviewed against published veterinary references. Awaiting credentialed clinical reviewer — our editorial process.

Cloudy, chalky urine in a rabbit is normal, which is exactly why bladder sludge gets missed. The owner of a rabbit with a bladder full of calcium paste often describes nothing more specific than a wet bottom, a rabbit that "sits funny," or droppings that have become smaller. By the time stranguria or obvious hematuria appears, the sediment has usually been accumulating for a long time.

This article walks through the pathophysiology, workup and management of hypercalciuria and sludge in the domestic rabbit. Drug doses are kept on the source-cited drug pages; the rabbit calculator handles weight-based math.

Why rabbit urine is full of calcium

Rabbits handle calcium differently from dogs and cats. Intestinal absorption is high and largely proportional to dietary intake rather than tightly regulated, so serum calcium tracks the diet and runs higher and more variably than in most mammals. The kidney is the main route of excretion, and the excess precipitates in alkaline rabbit urine as calcium carbonate. That's the creamy, opaque appearance owners notice, and in a healthy, active rabbit that drinks well and urinates frequently it causes no harm.

Trouble starts when excretion outpaces clearance. Crystals that would normally be voided settle in the dependent bladder, aggregate, and eventually form a thick paste that the rabbit can't empty. The same chemistry produces discrete calculi, most of them calcium carbonate, although calcium oxalate and mixed stones are also reported.

Sludge and stones are different problems

It helps to treat these as two related conditions rather than one. Sludge is a mobilizable sediment, and the core problem is that the rabbit isn't voiding it. Uroliths are discrete structures that can obstruct the urethra or ureters and won't flush out once they're of any size. Sludge responds to flushing, diuresis and husbandry changes. Stones usually need surgery or retrieval. Rabbits can have both, and a cystic calculus sitting in sludge is easy to miss on a single radiograph.

Causes: diet is only part of it

The usual dietary culprits are alfalfa hay, alfalfa-based pellets fed in large amounts, mineral or calcium supplements, and heavy use of high-calcium greens. Correcting these matters, but most rabbits with clinical sludge have a second problem that stops them from emptying the bladder properly:

The practical point is that changing the hay without addressing why an arthritic, overweight rabbit isn't moving will produce a short-lived improvement at best.

Clinical signs and differentials

Typical signs include urine scald and perineal dermatitis, a urine-soaked hindquarters, dysuria and stranguria, frequent small voidings, urinating outside the litter box, hunched posture and bruxism, hematuria, and reduced appetite progressing to gut stasis. Flystrike is a real risk in a rabbit with a wet perineum in warm weather.

Red urine needs sorting out before anyone reaches for an antibiotic. Porphyrin and plant pigments color rabbit urine orange to deep red and are harmless; a urine dipstick or sediment examination quickly separates them from blood. In an intact doe, blood seen at the end of urination may be uterine rather than urinary, and uterine adenocarcinoma or endometrial disease belongs on the list.

Radiographs, ultrasound and laboratory work

Radiographs are the workhorse. Sludge appears as diffuse, ground-glass to dense radiopacity filling the dependent part of the bladder, sometimes so dense that it looks like a single large stone. Discrete uroliths have defined margins. Image the whole tract, because nephroliths, ureteroliths and urethral stones in bucks change the plan, and look at the spine and joints for the reason the rabbit isn't moving.

Ultrasound is useful for distinguishing sediment from stones. Sludge is hyperechoic material that resuspends and swirls when the bladder is balloted, while a calculus casts a clean acoustic shadow and stays put. Ultrasound also assesses bladder wall thickness, the kidneys and hydronephrosis.

Urinalysis via cystocentesis gives sediment, specific gravity and culture. A positive culture should be treated, but don't assume one. Bloodwork should include renal values and calcium, interpreted with the understanding that rabbit serum calcium is naturally high and diet-dependent.

Flushing the bladder under sedation

For sludge, bladder flushing is the procedure that makes the biggest difference. It's done under sedation or light anesthesia, which most rabbits need anyway for adequate abdominal relaxation and analgesia. A urinary catheter is placed (the doe's urethral opening lies on the floor of the vagina, and bucks are catheterized as in other species), warmed sterile isotonic saline is instilled, and the bladder is gently agitated through the abdominal wall to resuspend the sediment before aspirating or expressing it. This is repeated until the returning fluid runs close to clear.

Be gentle. A distended, inflamed bladder wall is fragile, and aggressive manual expression of an overfilled bladder risks rupture. Some severe cases need more than one session.

Parenteral fluid therapy to promote diuresis supports the flush and keeps sediment moving afterward. Subcutaneous fluids are often adequate for outpatients. Some clinicians prefer saline to calcium-containing lactated Ringer's solution in these patients; the clinical significance of the small calcium content is debated.

When cystotomy is needed

Discrete cystic calculi too large to pass the urethra need removal, usually by cystotomy. The rabbit bladder wall is thin, so a careful closure and leak testing matter. Urethral stones in bucks can sometimes be retropulsed into the bladder and removed there. Ureteroliths and nephroliths are a different level of difficulty and are best referred. Submit stones for quantitative analysis, because a non-carbonate stone changes the dietary advice.

Sludge that has formed a dense, adherent cake sometimes can't be flushed and is removed at cystotomy as well. Don't treat surgery as the cure, though. Without the husbandry changes below, sludge and stones commonly return.

Analgesia and supportive care

Painful urination and a sore bladder stop rabbits eating. An NSAID such as meloxicam suits most patients, used with attention to hydration and renal values, and buprenorphine covers the more painful procedures. Managing the underlying musculoskeletal pain often does more for long-term bladder emptying than anything targeted at the bladder. Some cases with chronic osteoarthritis benefit from adding gabapentin, an extra-label use in rabbits.

Start assisted feeding early in any rabbit whose intake has dropped. If urinary tract infection is confirmed, choose antibiotics with the rabbit's hindgut in mind. Trimethoprim-sulfamethoxazole and enrofloxacin are common choices; oral penicillins, oral cephalosporins, clindamycin and lincomycin can cause fatal enterotoxemia and should not be used. Clean and dry the scalded perineum and keep it that way.

Hydrochlorothiazide is described in some references as an aid to reducing urinary calcium in recurrent cases. Evidence in rabbits is thin, and it doesn't replace diet and mobility changes. Doses and the supporting citations, where they exist, are on the drug pages, and the dosage disclaimer applies to all of them.

Diet, water and husbandry

The goal is a lower calcium load, not a calcium-free diet. Rabbits still need calcium, and dental and skeletal health suffer when owners overcorrect. The usual changes are to make grass hay such as timothy or orchard grass the bulk of the diet, switch from alfalfa to a timothy-based pellet and reduce the quantity, feed a variety of leafy greens while rotating away from the highest-calcium items, and stop mineral supplements and treats fortified with calcium.

Water intake is the change owners most often underestimate. A heavy ceramic bowl usually beats a sipper bottle, fresh water should be offered several times a day, and washed greens served wet add a surprising amount of fluid. More space, more exercise and gradual weight loss help the bladder empty.

Recurrence and follow-up

Recheck radiographs after flushing give a baseline, and repeat imaging at intervals catches recurrence before the rabbit is sick again. Many rabbits that have had sludge once will form it again, particularly if pain or obesity remains. The most common mistake is to flush the bladder, send the rabbit home on the same alfalfa and the same small hutch, and see it again with the same problem. Spend the discharge conversation on why the rabbit wasn't emptying its bladder, because that's the part owners can fix. Related urinary and reproductive presentations are on the conditions hub.

Hypercalciuria and Bladder Sludge in Rabbits, From Diet to Cystotomy | ExoticRx