The Association of American Feed Control Officials (AAFCO) requires guaranteed analysis, or a nutritional food content label, be printed on all pet food. It is similar in nature to the labels you find on the food you buy. Guaranteed analyses are performed in laboratories using a sample of the pet food. The analysis tests for crude protein, crude fat, crudo-fiber, and moisture percentages.
The AAFCO requires that pet food labels display at least the minimum percentage of crude protein and fat, as well as the maximum percentage of crudo-fiber and moisture. The reason that the label lists protein, fat, fiber, and moisture as minimum and maximum percentages is to take into account that every finished food product can vary in composition, amount of water removed, and mixing rates each time it is made.
Pet supplements are exempt from displaying crude protein, fat and fiber percentages because they don’t provide protein, fiber or fat. However, they must list the moisture percentages. If a food or supplement makes claims that it provides additional nutrients, then the guaranteed analysis label must display information to support the claim.