Ash in cat food is the inorganic mineral content left over when the organic portion of the food has been burned off. The mineral content can be any combination of calcium, magnesium, phosphorus, potassium, sodium, silicon, sulfur and other trace minerals.
Ash is measured by heating a food to 550 to 600 degrees – the inorganic residue is the “ash content”.
Confusion about ash content in pet foods developed as veterinarians and cat guardians were looking for the cause of Feline Lower Urinary Tract Disease (FLUTD – formerly known as FUS). In the 70’s & 80’s veterinarians thought ash was a factor in causing crystals in the urine. There are, however, a variety of causes and ash is no longer considered a factor in causing FLUTD. Further research has shown that the main problem was the formulation of commercial pet foods: most pet foods were creating a more alkaline urine (higher pH) which lead to an increase in struvite (magnesium ammonium phosphate) crystals. Dry kibble diets are mainly formulated with a high vegetable and grain content which creates a more alkaline urine (lower pH). An all meat diet such as a cat would eat in nature creates more acidic urine.
Magnesium content in foods has also been implicated in contributing to FLUTD. Magnesium content, however, is most likely a minor contributor compared to the influence of urine pH. Studies have shown that supplementing the diet with magnesium chloride did not cause urinary crystals to form in the urine as long as an acidic urine was maintained. Further studies have shown that if the urine is at a higher pH of 7.5 or more, struvite crystals will occur even if the diet is low in magnesium.
Magnesium is an essential mineral in the diet of cats and dogs for a variety of functions including energy production, proper muscle function, heart health, bone growth and dental health among others. Rather than the specific magnesium content of a food guardians would be better served by looking for the proper ratio of Calcium, Phosphorus and Magnesium in the diet which should be approximately Ca-1.3:P-1:Mg-.06. A deficiency of any essential mineral in an animal’s diet will eventually lead to mineral imbalance and disease.
Pet food manufacturers developed low ash and/or low magnesium foods in response to the theories that ash or magnesium were the cause of struvite crystals. When it was apparent that urine pH, and not ash or magnesium was the problem, they began to add Ammonium Chloride to their cat foods to acidify the diet. This practice, however, does not necessarily solve the problem since continued use of Ammonium Choloride can lead to a condition called chronic acidosis, which leads to mobilization of Calcium from the cat’s bones. The combination of chemically induced acidosis, calcium loss from the bones leading to increased calcium in the blood & urine, along with a reduced level of magnesium in the diet leads to the formation of oxalate stones. Oxalate stones have now become an increasingly common side effect of treatment for struvite crystals.
What to feed?
A high protein diet is the best way to maintain a low urinary pH naturally. Cats eating canned diets have fewer problems with FLUTD than those eating primarily dry kibble diets. This could be due both to the higher meat content of canned diets as well as the higher moisture content. Increased hydration also prevents crystal formation. A raw food or freeze dried diet is ideal for maintaining a lower urinary pH and providing proper hydration.
Cats do not drink water naturally; in the wild the moisture they consume comes from the moisture content of their prey. A cat eating dry kibble would need to consume approximately 8 oz. of water per day to prevent dehydration.
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