The percentages of nutrients shown in the guaranteed analysis section on a pet food label (protein, fat, fiber, moisture) are expressed “as fed” – meaning, as the food is delivered in its package. Some percentage of the food is comprised of moisture (water), which of course contains no protein, fat, fiber, or any other nutrient. Kibble generally contains about 10% moisture; canned foods usually contain about 78% moisture.
So, when a canned food label says that a food contains (for example) 9% fat, in order to reallyunderstand how much fat you are thinking about feeding to your dog, you have to remove the moisture from the equation; you want to know how much fat (in this example) is in the food part of the food – the “dry matter.” Any serious discussion of nutrition, or comparison of dry and wet diets, requires the conversion of the nutrient values from “as fed” to “dry matter.”
To calculate the nutrient levels in a food as dry matter (DM) percentages, first determine the amount of dry matter in the product. You do this by subtracting the percentage of moisture from 100. Then, divide the “as fed” percentage of the nutrient you are curious about by the amount of dry matter; that will give you the dry matter percentage.
For example, if a canned food has 78% moisture and 9% fat as fed (as seen on the guaranteed analysis):
100 – 78 = 22% dry matter (DM)