Back in the good old days, when it was time to feed Fluffy you'd give her some kibble and let her enjoy dinner. These days we have a better understanding of how diet impacts health. The appropriate ash content in cat food is one area that's changed.
Ash = Mineral Content
The basic parts of Fluffy’s food are fat protein, carbohydrates, fiber and moisture. When dry pet food is manufactured, the ingredients are incinerated to produce kibble. The inorganic residue left behind is referred to as ash, which is essentially the mineral content. All cats require minerals, including potassium, phosphorus, magnesium, zinc, iron, calcium and others. Though your cat may not need large amounts of these minerals, the proper amounts are essential to good health.
The Right Amount of Ash
In the 1980s ash content in cat food became important because it was thought it played a role in Feline Lower Urinary Tract Disease, or FLUTD. In response, vets often prescribed special cat foods that were low in ash, thinking it would help the urinary tract health of a cat with FLUTD. As it turned out it didn't do much at all to help the cats. In fact, it's since been shown that the overall ash level in cat food is not important. There is no "right" amount of ash in cat food.
pH Matters
Research has shown that Fluffy’s pH level in her urine is what really matters. If Fluffy has cystitis, her bladder wall is inflamed and producing excess mucous, which bleeds into her urine. If her urine pH is high, she'll have more magnesium in her urine, which is the key ingredient of struvite crystals – the most problematic of feline urinary crystals. If her urine pH is low, or more acidic, she's prone to calcium oxalate crystals. Understanding the pH of a cat's urine will help determine how to prevent the buildup of crystals that will cause FLUTD.
Minerals in the Diet
Ash content isn't important, but overall diet is. Understanding Fluffy’s urine pH level will guide some dietary choices. The relative content of magnesium, phosphorus and calcium are more important than the total ash content. If Fluffy’s urine pH is high, a food with a high magnesium content isn't for her because it will make her urine more alkaline, which will contribute to struvite crystal development. The National Academy of Science published daily recommended allowances for healthy cats that include .018 g calcium, 0.16 g phosphorus and 25 mg magnesium. Other minerals are listed in its publication “Your Cat's Nutritional Needs.” Of course, you should talk to your vet if Fluffy has health issues that may impact her diet options.