Let us immediately dispense with an old wives tale: No, kibble does not cause urinary stones. However, it is true that cats are more susceptible to the formation of calculi than other species, though occurrence is only 1%. Understanding of this affliction has improved in recent years. We now know that there are several types of urinary calculi in cats. The nutritional approach for treatment varies depending on the composition of the calculus. Not all urinary problems indicate the presence of calculi. A kidney disease or inflammation of the bladder (of bacterial origin or caused by a tumor) are equally common causes.
Symptoms of urinary calculi accompany the onset of what was previously known as feline urologic syndrome (FUS). The current term, feline lower urinary tract disease, is more accurate (FLUTD). Common symptoms include: Frequent trips to the litter box, straining, painful urination, and bloody urine. If a stone travels to the lower urinary tract, the urethra may be blocked. In this case, the cat is unable to urinate, and if left untreated, will die within 24 to 48 hours.
Magnesium ammonium phosphate stones (struvite) were much more common prior to the 1990s, before most manufacturers revised the composition of their foods. These types of stones are most common in young male and female cats between one and six years of age. Male cats, due to the structure of their anatomy, have greater difficulty expelling stones. Sterilized, sedentary, obese, or inactive cats generally urinate less frequently. When urine remains in the urinary tract for extended periods of time, a cat is predisposed to formation of stones.
Urine pH is by far the most important factor in the formation of struvite. A slightly acid pH (below 6.5) inhibits formation of stones. Conversely, alkaline urine favors mineral precipitation, particularly if there is a high concentration of magnesium. Dietary recommendations are simple: Food must create an acidic urine and contain a limited quantity of magnesium (less than 400mg/1,000 kg). Protein determines the amount of acidification. Proteins of animal origin generally increase acidity, whereas those of plant origin do not. Acidifying agents, such as methionine, ammonium chloride, or phosphoric acid (the most effective) may also be added. However, excessive acidity is also harmful. Chronic acidosis in an adult cat can lead to potassium loss.
In the early and late stages of life, acidification of urine is not recommended: In kittens, growth may slow and bone demineralization result. In cats over ten years of age, a different type of calculus is observed and, therefore, a more alkaline urine is appropriate.
Oxalate uroliths were very rare in the past, but their incidence is on the rise as a result of the dietary preventive measures mentioned above. This type of stone is most common in older cats. Males (neutered or whole) are more susceptible to this type of stone, as are certain breeds, including the Burmese, Himalayan, and the Persian. This type of calculus develops in alkaline urine containing high quantities of oxalate and calcium. Diet has an effect on the formation of this type of calculus. A diet rich in sodium, vitamin D, and lactose, but low in fiber and phosphorus improves intestinal absorption of calcium. The ideal diet should not acidify urine, be rich in magnesium, and have a low concentration of calcium.
The frustrating fact of the matter is that the nutritional recommendations for preventing the formation of struvite and oxalate calculi are directly opposing. Therefore, a middle ground must be found. Acidifying agents should not be administered if food promotes acidity. The focus should be on attaining moderate acidity_a pH of approximately 6.5, lower if there are struvite calculi to be dissolved. Note: Calculi must be analyzed before determining the appropriate dietary treatment. Finally, acidifying foods should be avoided for very young or geriatric cats.
In addition to food composition, the manner in which the food is consumed also plays a significant role. Urine concentration promotes formation of calculi of any type. Diluting the urine increases trips to the litter box and reduces the likelihood of stones. Cats should always have access to fresh water (replaced at least daily). Food quality also plays a role. If it is highly digestible and energy-rich, water loss resulting from defecation will be kept to a minimum.
Moreover, researchers have established that the secretion of stomach acids during digestion makes urine more alkaline. The greater the amounts of food consumed, the greater this effect.
Therefore, feeding several small meals is recommended. Free feeding of dry foods (within daily quantity guidelines) encourages the cat to drink more often and therefore promotes more stable urine acidity. Finally, during hot weather, a cat should have access to a cool area, because urine pH rises sharply in extreme weather conditions.
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