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Bladder Stones And Sludge

Bladder stone. Bladder stones (also called uroliths or urinary calculi) are hard, stone-like structures usually composed of calcium carbonate which form in the bladder.

Bladder sludge is a term used to describe gritty calcium-based particles that collect in the bladder.

Kidney stones can also form in the kidneys and ureters but this is less frequent and may not be treatable.

Stones can become lodged in the urethra slowing or completely blocking urination. This is especially dangerous for boars, as their urethra is narrower than that of a sow.


Any guinea pig with stones should be treated promptly.

X-ray of bladder stones and ureter stones

Stone photo contributed by Trisha. Stone is about 3/4" wide (2cm).

X-ray contributed by Sef (Sandra).

SIGNS OF STONES X-ray of guinea pig with bladder stone.

  • Blood in urine
  • Squeaking while urinating
  • Squeaking while passing fecal pellets

Your guinea pig may be hunched or strain while urinating or passing feces or may show general signs of illness like changes in appetite, depression, or decreased activity. Stones can sometimes cause so much pain that they interfere with mobility. The only change a few pet owners noticed was heavy breathing, most likely indicating pain. So if something seems "off", stones may be a possibility.

Photo contributed by Piggielove.

Differential Diagnoses (other possible conditions)

Sometimes no stones and no infection are found.

If the diagnosis is interstitial cystitis, following the prevention guidelines on this page and providing pain medication (like Meloxicam) may help. Go Up

What Your Vet Will Do X-ray of bladder stone and sludge.

Your vet will examine your guinea pig and palpate the lower abdomen. Stones cannot always be felt by palpation.

An x-ray (two views) must be taken to determine if bladder stones are present.

An ultrasound can also be used to check for the presence of stones.

Your vet may test for a UTI by collecting urine or drawing it directly from the bladder using a needle (cystocentesis). Urine is checked for bacteria and blood. If there is no visible blood, the urine may be tested for the presence of blood. Go Up Photo contributed by Sef (Sandra).


Most guinea pigs cannot pass bladder stones on their own and require surgery to remove them. Bladder stones in the urethra can sometimes be plucked from the urethra if close to the opening. A page at Maryland Veterinary Surgical Services website describes a typical cystotomy.

If your veterinarian does not have experience with bladder stone surgery, ask for a referral.

Occasionally a guinea pig passes a stone before surgery so a pre-surgery x-ray is recommended to locate the stone. Bladder stones that have entered the urethra are sometimes flushed back into the bladder for surgical removal. Two or more weeks of an antibiotic like Bactrim (trimethoprim/sulfamethoxazole) can help prevent infection while the bladder is healing and will treat most urinary tract infections.

Multiple Stones

Because new stones may reform within months or even weeks of surgery, it is important to monitor your pet's health after stone removal. Some pet owners report the recurrence of stones 2-3 weeks post surgery. An x-ray of AliceMcmallis' guinea pig showed it stone-free, but the following week an x-ray showed 3 stones. Nutz4pigs's Louie formed a second large stone only 3 weeks or so after his previous stone surgery. Other pet owners tell similar stories.

Susan Brown, DVM recommends routine veterinary rechecks to monitor rabbit health following stone removal: "A urinalysis should be performed several times during the first few weeks after surgery or catheterization to detect any infection or increase in mineral formation. A physical examination should be performed post-surgically to evaluate healing of the bladder and abdomen. Radiographs should be performed within six months initial treatment to look for the return of stones or sludge in the urinary tract. Please follow your veterinarian's recommendations on recheck visits." From Go Up


The cause of bladder stone formation is poorly understood. Because stones seem to run in families, it is likely there is a strong genetic component. Frequent urinary tract infections have also been implicated, as well as improper diet, inadequate water intake, and obesity.

Stone Composition

Calcium carbonate is the most common type of stone. Recent studies have shown that the composition of the majority (90%>) of urinary stones in guinea pigs is 100% calcium carbonate. A certain percentage also contain traces of calcium phosphate, oxalate or struvite (1). Pure calcium phosphate or struvite stones are extremely rare. If calcium oxalate is detected, it may be attributed to a high oxalate diet.(2) It is not uncommon for a calcium carbonate stone to be misidentified.

Stone analysis may aid in developing prevention strategies. "A high pH value and high urinary calcium concentration are crucial for calcium carbonate crystallization in urine."(2) This would suggest an overall reduction in calcium intake may be helpful.

Neiger Hesse emphasizes the importance of phosphorous in the diet. An overall ratio of between 1.5:1 and 2:1 (calcium to phosphorus) is a generally accepted standard. Magnesium, vitamin D and C along with other vitamins and minerals are also necessary for good health.

(1) Composition and Characteristics of Urinary Calculi from Guinea Pigs by Hawkins, et el, JAVMA Vol 234, No, 2, January 15, 2009

(2) Urinary Stones in Small Animal Medicine by Neiger Hesse, Manson Publishing, 2009


A good quality diet is thought to help prevent the formation and reformation of bladder stones. Poor diets consisting primarily of alfalfa pellets but low in hay and vegetables may contribute to stone formation. "Guinea pigs should be fed hay and fresh greens to minimize the risk of urolith formation...with the benefit of preventing [obesity]" [R. Jolankai, et al.; Urolithiasis in Guinea Pigs--Nutritional Aspects; 2006]

A good diet will include:

  • Unlimited high quality grass hay
  • A variety of vegetables (mostly leafy greens)
  • Limited (or no) low-calcium guinea pig timothy pellets
  • Increased fluids

Grass Hay

Grass hay should be the foundation of every guinea pig's diet. Offer the best hay you can find to encourage eating as much as possible.


Guinea pigs are herbivores. Their digestive system is designed to extract nutrients from a variety of grasses and greens. Wet, leafy greens are a good choice. Fruits, generally high in sucrose and other sugars, can be added as treats. Forages are a good supplement to your guinea pig's diet. See the information on the Calcium:Phosophorus ratio below.


Use a lower calcium timothy pellet and consider limiting or using no pellets at all. Some timothy guinea pig pellets have added calcium. Some owners report better management of bladder sludge by feeding KMS Hayloft pellets, which are lower in calcium and sodium than most commercial brands. If you severely limit or remove pellets, extra care must be paid diet by offering a wide variety of appropriate vegetables (with a few fruits) for their added vitamin and mineral content.

  • Vitamin D is required for proper absorption of calcium. For a guinea pig lacking regular exposure to sunlight, removing pellets may result in a diet devoid of vitamin D. Vitamin D is not present in hays and greens but is added to most guinea pig pellets. If you will be going pellet-free, consider a vitamin D supplement. Your vet can recommend a specific dose.

Nutrient Requirements of Laboratory Animals, Fourth Revised Edition, 1995 reports that a vitamin D requirement for guinea pigs has not been established "but currently used natural-ingredient and purified diets contain between 20 and 180 nmol/kg diet... seem to promote growth at rates that were average for the colony. The requirement for growth is set at 1,000 IU vitamin D/kg diet (65 nmol/kg diet; 0.025 mg/kg diet)." Note that their recommendations refer to the amount of vitamin D per kilo of food, not per day per animal. A guinea pig does not eat a kilo of food per day.


Take every opportunity to increase fluid intake.

  • Wet down leafy greens.
  • Keep water bottles clean and fill regularly with fresh water.
  • Use multiple water bottles to encourage drinking.
  • Offer fluids by syringe or administer subcutaneous injections of fluids twice a week (or as recommended by your veterinarian).
  • Do not add vitamin C to water (changed taste may discourage drinking).
  • Filter hard water to reduce calcium and remove impurities.


The low incidence of calcium oxalate stones may indicate that for the majority of guinea pigs, dietary oxalate is not a contributing factor in stone formation. Dietary oxalate binds with calcium. Often foods higher in oxalic acid are also higher in calcium, providing the calcium needed to bind with the oxalate.

Note: Oxalic Acid Content in Foods is an excellent list, providing sources and pointing out the discrepancies among them. For example, the USDA Agriculture Handbook No. 8-11, Vegetables and Vegetable Products, 1984 rates carrots at 1/2% oxalate while Litholink's rates carrots at 0% oxalates.

The Calcium::Phosphorus Ratio

Most studies of animal nutrition recognize the importance of a proper calcium phosphorus ratio to good health. While it is likely an overall lowering of calcium in the diet will help prevent the formation of stones, calcium is still essential to bone growth and many metabolic functions.

Check the Nutrition Chart for information on calcium and phosphorus content and Ca:P ratios. Combine a variety of vegetables (and a few fruits) low in calcium, aiming at an overall ratio of between 1.5:1 and 2:1 (calcium to phosphorus). If you wish to evaluate the diet you are providing, the Excel Calculator makes it easy. Enter the weight of foods in grams and automatically generate a calcium:phosphorus ratio for a day's worth of foods, along with Vitamin C amounts. Go Up

Read Dawn Hromanik's comments on stone formation and Ca:P ratios originally posted in the Reference Forum. The rule of thumb that I use is that all vegetative parts of plants have a higher Ca:P ratio. This is ideal, you do *not* want the inverse where the phosphorus is higher than calcium. (this can [con]tribute to phosphate stones and bone demineralization) Phosphate crystals embed themselves in the bladder wall and are very irritating. Reproductive parts of plants (seeds and roots) have a higher Ph content. This includes all fruit (apples, bananas, grapes, raisins), seeds (treat mixes, sunflowers, oatmeal etc), and carrots. Just another reason not to feed the above food. Go Up


Increased exercise may encourage more fluid intake and help keep sediment from forming in the bladder. In addition, exercise helps keep weight under control and can improve overall guinea pig health and happiness!


Keep bedding clean and dry. A guinea pig that sits in the same spot for long periods of time (which may be wet and harbor bacteria) may be more prone to develop urinary tract infections. Trim butt hairs to help limit the growth of bacteria that can be aggravated by continued wetness. Remove houses during the day to encourage more changes of location. Or change the location of sleeping areas and switch out sleeping pads frequently. Plastic grid-like tiles (see alternate bedding) allow drainage of urine to an absorbent material below.



Actigall (Ursodiol) has been used for the treatment of stones. However there may be risks to hindgut fermenters like rabbits and guinea pigs and it is not clear that Actigall helps. Tracis has compiled a thread on the use of Actigall (Ursodiol) for the treatment of stones.


Polycitra (Urocit-K) is a prescription medication used to increase urine alkalinity and bind calcium, helping to prevent the formation of calcium oxalate stones in cats and dogs. Since guinea pigs naturally have alkaline urine (8.5 pH>) and usually do not develop oxalate stones, Polycitra may not be beneficial. However, urinary tract infections, kidney diseases, and genetic predispositions can lower citrate in the urine. Although urine pH is seldom tested by vets, urine analysis may be useful in determining whether or not Polycitra is having the desired results.

An article at Marvistavet explains how oral treatment works for cats and dogs by increasing citrate levels in the urine and allowing the calcium to bind to the citrate instead of to oxalate. Since calcium citrate tends to stay dissolved, it is more likely to be passed in the urine. Calcium oxalate, on the other hand, tends to precipitate out as mineral deposits. As noted above, most guinea pig uroliths are calcium carbonate. Calcium oxalate may also be passed through the urine.


A Chinese herb called "shilintong" has reportedly helped some guinea pigs manage pain and inflammation. Shilintong's Chinese name is Guang jin qian cao; the scientific name is Desmodium Styracifolium according to a half dozen online sources. Its pharmaceutical name is Desmodii Styracifolii (only one source) and the common name is Snowbell-leaf Tickclover Herb (several sources).

GP Lover, a forum member, dissolved 1 pill in about 2.0 cc water and syringed 1.0 cc to her guinea pig Angel twice/day. Since the pills are coated and very hard, soak first for several minutes in water and then crush. Shilintong can be purchased from

"Effect of Desmodium styracifolium-triterpenoid on calcium oxalate renal stones" at Pub Med describes the effect of a drug (Desmodium styracifolium-triterpenoid [Ds-t]) extracted from Desmodium Styracifolium on stones in rats with induced calculi.

    "The incidence of urinary stone formation was 81% in the control group, which received EG and 1 alpha D3, and 29% in the Ds-t group, which received EG and 1 alpha D3 supplemented by Ds-t."

Several Pub Med articles reference shilintong. A Chinese study of the anti-inflammatory effects of two species of Lysimachia christinae Hance and Desmodium styracifolium (Osbeck) Merr. is listed in the database. Go Up

Important Side Note

Unfortunately, there are no sure-fire methods to prevent stone formation. Despite following every guideline and providing the best of care, these dreaded stones can still return. After all the hours the author has spent on this page reviewing information, she is left with more questions than answers. Perhaps one day we will understand how to keep our guinea pigs stone-free. But for now, we can only make sensible changes to try to stop their formation and recurrence.

Thanks to Sef (Sandra) for her research, contributions, and prodding!

Guinea Pigs are for Life