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Old July 4th, 2008, 03:11 PM
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sugarcatmom sugarcatmom is offline
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Originally Posted by kathryn View Post
Magnesium has to do with urinary health right? Or is that something else.

I've read about urinary PH has to do with something else, and cats can get UTI's if they have too much of something. And I think at one point I read too much ash = UTI's.
Magnesium is only a factor in FLUTD as it relates to urine PH. The more alkaline the urine, the more likely magnesium will play a role in struvite crystal formation. The ash=UTI thing is old school. Current thinking is that a meat-based wet food diet is the most important element in avoiding bladder/urinary tract problems in cats.


Magnesium is probably the mineral of the most concern in cat nutrition for owners, and especially to owners of male cats because of its role in the formation of struvite uroliths (magnesium ammonium phosphate). However, magnesium is not a "bad guy". Magnesium is a macromineral, its amount in the body is much lower than that of calcium and phosphorus. Approximately 60% to 70% of the magnesium found in the body exists in the form of phosphates and carbonates in bone. Most of the remaining magnesium is found within cells, and a very small portion is present in the extracellular fluid. In addition to its role in providing structure to the skeleton, magnesium functions in a number of metabolic reactions; a magnesium ATP complex is often the form of ATP that is used as a substrate in many of these processes. As a cation in the intracellular fluid, magnesium is essential for the cellular metabolism of protein. Protein synthesis also requires the presence of ionized magnesium. Balanced in the extracellular fluids with calcium, sodium, and potassium, magnesium allows muscle contraction and proper transmission of nerve impulses.

A commercial cat food should not be selected only on the basis of its magnesium content. The quantity of magnesium required to saturate urine with struvite at alkaline pH is very small. As pH decreases below 6.4, the amount of magnesium required to saturate the urine with struvite increases exponentially. Conversely, as urine pH increases above 6.9, the amount of struvite that forms in the urine increases markedly. When urine pH is alkaline, the amount of struvite formed in urine is proportional to the dietary magnesium concentration. At urine pH values less than 6.1, struvite does not form regardless of the magnesium concentration of the diet. Thus, the tendency of struvite to form is a function of urine pH. The magnesium content of the diet only becomes important when urine pH is greater than 6.1.

The food's caloric density, digestibility, and urine-acidifying properties should all be considered when selecting a commercial cat food for the prevention of struvite urolithiasis. Constituents of foodstuffs exert major effects on urine pH. Sulfur-containing amino acids, phospholipids, and phosphoproteins naturally found in a carnivorous diet naturally acidify the urine, whereas salts of organic acids alkalinize it. Salts of dietary organic acids, which come primarily from plant material and found in high quantities in dry food, have an alkalinizing effect.

The percentage of magnesium in the diet is not as important as the total amount of magnesium that a cat consumes. Diets that are moderate in caloric density and are highly digestible will be consumed in smaller amounts, thus lowering both DM and magnesium intake. High-quality canned food is typically >90% digestible whereas equal quality dry food is ~80% digestible. The lower DM intake results in decreased fecal matter and fecal water and increased urine volume. Feeding a canned diet with these characteristics further contributes to increased urine volume and decreased urine specific gravity reducing the risks of urolithiasis while supplying the cat's dietary magnesium requirements. Although many brands of dry cat food may contain relatively low concentrations of magnesium, they are often lower in digestibility than canned and contain high levels of cereal grains. Because the cat's requirement for dietary magnesium is substantially lower than the amount usually found in cat food, a general rule of thumb is to select a high-quality, highly digestible, canned food that contains 0.12 % magnesium or less.
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