Ca:P & POLYCITRA
Understanding the Ca/P Ratio and the Role of Polycitra
Polycitra is a prescription medication. See your vet to discuss its use.
Why a diet with a proper calcium to phosphorus ratio?
Calcium, phosphorus and magnesium are three essential minerals found in the bodies of vertebrates. These minerals are used for numerous functions, including building bones and teeth, muscle contraction, blood clotting, maintenance of cell membranes, and nerve transmission.
Basically, guinea pigs, like rabbits, absorb any and all calcium that is made available to them. Excess calcium is filtered in the kidneys, passed into the bladder and expelled. Humans, on the other hand, tend to only absorb the calcium they need at any given time.
There are two levels of calcium guinea pigs have available to them. Highly digestible calcium is the calcium that can be absorbed by the body and is not bound to another substance preventing its absorption into the GI tract. This is the type of calcium found in alfalfa and commercial pellets. Lower digestible calcium is found in plant materials. In simplest terms, most of the calcium binds to oxalates, making them more available for cellular use.
Calcium and phosphorus (and magnesium -- haven't gotten that far, so I won't address it yet) have interactions between them that affect their availability or absorption in the body.
A saying in animal science, (who are a not-very-poetic bunch and pathetically easy to amuse), is "as goes phosphorus, so goes calcium". What this means is that for every gram of phosphorus ingested in the diet, the body must match that with another gram of calcium before the phosphorus can be absorbed through the intestinal wall into the bloodstream. (1)
I won't pretend to completely understand how this interaction works, however, there is evidence (2) that a certain percentage of stones are caused by an imbalance of calcium and phosphorus in the diet. This also is the reason to avoid carbohydrates, grains and excess amounts of sugar, particularly processed sugar, in the guinea pigís diet. Grains have an inverse ratio of phosphorus to calcium and can cause stones to form. (2)
Where does Polycitra fit into all of this?
Citrate is the primary agent for removal of excess calcium in the urine.
...citrate binds to calcium ions in the urine, reducing calcium ion activity, which results in lowering the urinary supersaturation of calcium phosphate and calcium oxalate. Second, citrate has a direct inhibitory effect on the crystallization and precipitation of calcium salts. (3)
The more alkaline the urine, the more citrates are present to aid in the bonding of excess calcium. Since guinea pigs naturally have alkaline urine, many vets don't think polycitra would be beneficial. However, urinary tract infections, kidney malfunctions and diseases, and genetic predispositions can lower the amount of citrate in the urine. Since most vets don't bother to test the Ph of guinea pigs, it isn't possible to know if stone or sludge pigs have a sufficient amount of citrates.
The following is an explanation for canine/feline stones, however, itís a good explanation of how polycitra works aside from making the urine more alkaline.
By taking potassium citrate orally, citrate levels increase in the urine. Calcium binds to citrate instead of to oxalate which is a desirable event since calcium citrate tends to stay dissolved whereas calcium oxalate tends to precipitate out as mineral deposit. (4)
Source (1) www.shady-acres.com/susan/probiotics.shtml
Source (2) www.petcarevabeach.com/guineafood.html
Source (3) www.emedicine.com/MED/topic3030.htm
Source (4) www.marvistavet.com/html/body_canine_oxalate_bladder_stones.html
Source (5) adam.about.com/reports/000081_2.htm
Sample Diet -- The Ca:P Ratio in Action
Calculator -- Quick Ca:P & Vitamin C Excel Calculator