Ash content

What ash actually measures

Ash is not an additive. It is a laboratory result: a weighed food sample is heated to roughly 550 °C until everything organic burns off, and what remains is the 'crude ash'. That residue is essentially the total mineral fraction of the diet, expressed as a percentage.

Dry kibble typically runs 5–8% ash. Canned foods, calculated on an as-fed basis, look lower (1–2%) because of their water content; on a dry-matter basis they land in the same range. Higher-ash foods generally contain more bone-derived ingredients.

Where the worry comes from

In the 1970s, high dietary magnesium and ash were implicated in struvite crystal formation in cats. That association drove the original 'low ash' marketing. Modern feline nutrition has refined the picture: urinary pH and specific mineral ratios matter more than total ash, and reputable maintenance and urinary diets are formulated for those targets directly.

How to use the number on a label

If a guaranteed analysis lists ash, compare like with like, dry to dry, wet to wet on a dry-matter basis. A wide gap between two otherwise similar foods (e.g. 5% vs 10% on a dry basis) usually signals different amounts of bone-bearing ingredients. For most healthy cats and dogs the number is not actionable on its own; for cats with a confirmed urinary history, follow your vet's diet recommendation rather than chasing ash percentages.

Why it matters

Ash gets used in marketing as if lower is automatically better. It isn't, the right mineral profile for a growing large-breed puppy, an adult cat, and a senior dog with kidney disease all look different. The number only matters relative to your animal's specific need.