In the body, calcium is used in a variety of metabolic processes; the one most commonly thought of is the maintenance of bones (including teeth) and muscles. Guinea pigs, like rabbits, absorb all of the calcium made available to them in their diet. All other mammals (humans included) basically absorb only the calcium that their body needs at the time; any excess calcium in the diet would simply not be absorbed. If a bit of excess calcium would happen to be absorbed, it would then be passed through the gastrointestinal tract and excreted in the feces.
The guinea pig and the rabbit, however, absorb ALL the calcium that they take in whether their body needs it or not, and then pass along all that excess calcium through to their kidneys, where it is filtered, passed along into the bladder and then excreted in the urine.
The calcium that is passed out of the body in the urine is what makes normal rabbit and guinea pig urine appear cloudy as compared to the urine of other mammals. If the urine is very white however, and leaves white deposits after it dries, this can indicate that your pig is getting too much calcium in its diet. Guinea pigs need a certain amount of daily calcium, but too much calcium buildup in the bladder and urinary tract can contribute to the formation of bladder stones and sludge.
Many veterinarians believe that the formation of bladder stones is not solely caused by dietary factors, but that certain genetic factors can make particular guinea pigs more susceptible to stones. High levels of calcium in the diets of those guinea pigs can then cause the bladder stones to form more easily. If your guinea pig is prone to forming stones, you need to carefully monitor the calcium that is in their diet, and avoid foods that supply calcium in significant amounts. Alfalfa-based pelleted feed and hay should be avoided in favor of timothy-based guinea pig feed and hay. Alfalfa pellets offer the greatest concentration of dietary calcium in a food that is easily consumed in large amounts.
Increasing your guinea pig’s consumption of water can help flush the urinary system and even get smaller stones and sludge to flush through. In addition, pure unsweetened cranberry juice is beneficial to the urinary tract and may also entice your pet to consume more fluids. Set out a small amount of the juice and be sure to change it after a few hours to prevent the formation of bacteria.
Even guinea pigs predisposed to bladder stones and sludge still need daily calcium in their diet; the trick is in moderation. Do not feed vegetables high in calcium every day. High calcium foods include dark green leafy vegetables such as spinach, kale, collards, mustard greens, dandelion greens, and parsley. Medium calcium content vegetables include Romaine, Boston, and bibb lettuces. Lower calcium content vegetables should be fed more frequently, and these include red and green bell peppers, carrots and cucumber.
Fruit should not be a staple of a guinea pig diet, but if you are giving them as occasional treats, you should know that low calcium fruits include peaches, blueberries, bananas and cranberries; the latter being beneficial to urinary health. High calcium fruits include oranges, blackberries and raisins. Your exotics veterinarian can further guide you on proper diet.
GuineaLynx has a great list of calcium content for vegetables and fruits for further reference.
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