The contents of your fireplace is not being added to your pet’s diet so don’t worry, ash is not a dirty word in this instance!
“Ash”, as it appears on the guaranteed analysis label of pet food is another term for the incombustible part of these essential dietary minerals (such as calcium, iron, potassium, etc).
Minerals are inorganic nutrients in a diet and when foods are analyzed for energy all nutrients other than minerals are removed and the remaining material is dietary minerals which are referred to as “ash”. It is part of the essential nutrient intake that your cats and and dogs need so don’t worry, let them eat up!
Some cats and dogs with specific health issues do require their veterinarian to closely monitor a pet’s intake of certain minerals and adjust the mineral content and the level of ash in their diet.