"Ash" in dog food doesn't refer to the common ash we think of. Instead, it represents the incombustible mineral residue that remains after the food undergoes high-temperature laboratory testing. Essentially, when dog food is completely incinerated, the protein, fat, and carbohydrates burn away, leaving only the mineral content behind.
These minerals, which include elements like calcium, phosphorous, zinc, and iron, are vital for your dog's health. The term "ash" is a standardised way to communicate this mineral content on dog food labels, and its a regulatory requirement to include the ash percentage on dog food packaging. It's not a filler or an unwanted additive; rather, it's an indication of the essential minerals present in the food.