• The Guinea Pig Vet


The Guinea Pig Vet on : Calcium phosphorous ratios and Bladder Stones in Guinea Pigs.

I’ve been asked many times about medical and dietary management of bladder stones in guinea pigs and especially Calcium:Phosphorous ratios. I thought I would write this blog to try to explain more of the detail and follow up on previous posts on my facebook page.


Unfortunately, bladder stones (urolithiasis) are very common in the guinea pig. Stones in guinea pigs appear to universally be calcium containing salts; these can include calcium oxalate, calcium phosphate or calcium carbonate. In my experience calcium oxalate seems to be the most prevalent.


Efforts have been made to reduce the occurrence of bladder stones by dietary management. At the moment there appears to be no diet that will dissolve bladder stones in guinea pigs (as can be the case for some stones in dogs). However, it may be possible to reduce occurrence or reoccurrence rates by reducing dietary calcium, more specifically paying attention to the Calcium:Phosphorous (Ca:P) ratio of foods.


Calcium is found in three compartments in the body, the blood and extracellular fluid (ECF), within cells, and in teeth and bones. Calcium plays a role in many important processes in the body including muscle contractions, nerve impulses and blood clotting. As a result, the levels of calcium in the body are under tight control and should not be restricted completely. Excessive restriction can cause problems with these processes or the development of weak teeth and bones. The hormones that are involved in calcium homeostasis include parathyroid hormone (PTH), calcitonin and Vitamin D.


PTH is produced by the parathyroid glands, levels of PTH increase in the body in response to high phosphorous or low calcium levels in the blood. PTH acts on the skeleton to cause the release of Calcium, the kidneys to increase calcium reabsorption from the urine (and increase Vitamin D production), and the intestines to increase Calcium absorption from food. This has the effect of increasing blood calcium levels.


Calcitonin is produced in the thyroid glands; it opposes the action of PTH. Therefore, levels of calcitonin increase with high levels of calcium in the blood. Its actions reduce blood calcium. It inhibits osteoclasts (reducing calcium release from bones) and reduces calcium reabsorption by the kidneys (therefore increasing urinary calcium).


Vitamin D plays a role in regulating calcium absorption from the intestines, as well as urinary calcium excretion and bone metabolism.


The absorption, metabolism and excretion of Calcium and Phosphorous are intimately related; with other elements such as potassium and magnesium also playing a role.

The take home message is that there isn’t a simple answer. It isn’t the case that if you feed less than ‘X’ grams of calcium per day bladder stones are less likely. It is true that Ca:P is more important, it is generally thought that a ratio of 1.5:1 (Ca:P) or less is beneficial. (Veg that fulfils this criteria can be found on the guinealynx website).


If bladder stones are Calcium Oxalate then reducing dietary oxalate sources can also benefit. Oxalate content is high in things such as spinach, parsley, celery and strawberries. Vitamin C can contribute to urinary oxalate levels. Vitamin C is important in the diet of guinea pigs as they cannot produce their own however high levels should be avoided in guinea pigs prone to calcium oxalate stones.



Other factors can contribute to stone formation for example infections, inflammation and bleeding in the bladder, very concentrated urine, and stress. So, attention should also be paid into addressing these issues.

  • The Guinea Pig Vet

I thought I would talk about cystic ovaries since elective neutering has been a contentious issue.


It is not yet routine in the UK to neuter female guinea pigs. However, cystic ovaries occur in around 80% of adult females (over 4 years if age). Cystic ovaries may or may not produce hormones. Those that do will cause clinical signs such as increased sexual or aggressive behaviour, hair-loss, sometimes mild weightloss and blood in the urine. Those that are non-hormone producing, if small, may have no clinical signs. If they become very large  (5cm or more in diameter) they may cause gut motility issues and increased respiratory effort, due to pressure on the diaphragm.


Treatments that have been attempted include drainage of the cyst, hormone treatment or surgical removal.

  • Drainage is via a needle inserted through the skin in a conscious or mildly sedated animal. Risks include leakage of fluid into the abdomen which can result in adhesions forming between organs, affecting gut motility. It would not improve symptoms if the cyst was hormone producing.

  • Hormone treatment involves the use of a medication called chorulon (human chorionic gonadotrophin) but it's efficacy is probably only 50% and it is expensive.

  • The treatment of choice is surgical removal of the ovaries. Ideally this is performed via a surgery called a bilateral flank ovariectomy. Where the ovaries only are removed through 2 small incisions. This type of surgery has much lower impact on gut motility post operatively than a midline spey.

So why don't vets routinely remove ovaries pre-emptively as in dogs and cats?

The surgery in guinea pigs is technically more challenging with risks of post-op gut stasis. In addition, general anaesthetic in guinea pigs still carries greater risks than in dogs and cats. Some studies suggest anaesthetic deaths in otherwise healthy guinea pigs averages 1 in 75. So there is a weigh up between the anaesthetic risk and the prevention of possible future symptoms resulting from cystic ovaries. The debate over the right decision to make will likely continue for some time.


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  • The Guinea Pig Vet

Guinea pigs, like rabbits, can be prone to teeth and jaw problems. This is mainly due to the fact that their teeth grow constantly. Signs that indicate a teeth or jaw problem include a change in eating habits (i.e. eating less, choosing to eat soft vegetables, not eating hay), increased salivation and a change in the angle of the occlusal surface of the incisors (the surface where the incisors meet). If you notice any of these signs, you should consult a vet.

Normally, the incisors teeth will wear completely horizontally. If this starts to become a slope (as in Myrtle's case as seen on Facebook), it is a sign there is a problem with the way your guinea pig is eating. This problem could be mouth pain (caused by wounds or molar spurs) or jaw pain (most commonly caused by abscesses).

Slanted guinea pig incisorsSlanted guinea pig incisors
Myrtle's slanted incisors