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.