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It is common and normal for rabbits to have a thick, white urine due to calcium carbonate precipitate. It is also common to observe calcium concentrations between 3–4 mmol/l (12–16 mg/dl) in the serum of normal rabbits.
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| What is unique about calcium metabolism in the rabbit? | Rabbits are unique in their methods of absorption and excretion of calcium. Many species of animals absorb and control calcium in relation to their metabolic needs, regulated by the parathyroid hormone interacting with metabolites of vitamin D and calcitonin. Rabbits appear to absorb calcium from the gut in direct proportion to the concentration in the diet. This absorption appears to be independent of metabolic need.
It is still unclear as to the role that vitamin D plays in calcium absorption in the rabbit. The primary route of calcium excretion is renal. When the blood calcium level exceeds the kidney threshold, the excess blood calcium is excreted in the alkaline urine. This is different than other species where the bile is the primary route of removal. Plasma calcium concentrations can change dramatically depending on the amount of calcium in the diet. ‘High’ plasma calcium concentrations from 3–4 mmol/l (12–16 mg/dl) are commonly found in rabbits on a calcium-rich diet, such as those eating alfalfa-based pellets and alfalfa hay. |
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| What factors could increase calcium carbonate precipitation in the urine? | The two most common factors are increased dietary calcium and an increase in the urine pH.
The form of the calcium in the diet also influences its digestibility. For instance calcium oxalate is about 49% digestible, dicalcium phosphate is about 53% digestible and calcium carbonate is about 81% digestible. The rise of urine pH may be associated with urinary tract infection. In addition, inadequate water intake can obviously lead to a more concentrated urine. The role vitamin D plays in calcium metabolism in the rabbit is controversial. Some studies indicate that high dietary concentrations of vitamin D along with high dietary calcium concentrations may predispose the rabbit to calcification of the aorta and kidney, but this is not always reproducible. For this pathology to occur, it may be necessary to maintain high concentrations of vitamin D and calcium for prolonged periods or there may be other unknown metabolic or dietary factors involved. |
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