A pet food label must state guarantees for the minimum percentages of crude protein and crude fat, as well as the maximum percentages of crude fiber and moisture. The "crude" term refers to the specific method of testing the product, not to the quality of the nutrient itself.

Guarantees are declared on an "as fed" or "as is" basis, that is, the amounts present in the product as it is found in the can or bag. This doesn't have much bearing when the guarantees of two products of similar moisture content are compared (for example, a dry dog food versus another dry dog food). However, when comparing the guaranteed analyses between dry and moist (raw/canned) products, one will note that the levels of crude protein and most other nutrients are much lower for the moist product.

This can be explained by looking at the relative moisture contents. Moist foods typically contain 65-78% moisture, whereas dry foods contain only 10-12% water. To make meaningful comparisons of nutrient levels between a moist and dry product, they should be expressed on the same moisture basis.

The most accurate means of doing this is to convert the guarantees for both products to a dry matter basis. The percentage of dry matter of the product is equal to 100% minus the percentage of moisture guaranteed on the label. A dry food is approximately 88-90% dry matter, while a moist food is only about 22-25% dry matter. To convert a nutrient guarantee to a dry matter basis, the percent guarantee should be divided by the percentage of the dry matter then multiplied by 100.

For example, a moist food guarantees 12% crude protein and 75% moisture (or 25% dry matter), while a dry food contains 27% crude protein and 10% moisture (or 90% dry matter). Which has more protein, the dry or moist? Calculating the dry matter protein of both, the moist contains 32% crude protein on a dry matter basis (12/25 X 100 = 48), while the dry has only 30% on a dry matter basis (27/90 X 100 = 30). Thus, although it looks like the dry has a lot more protein, when the water is removed; the moist food actually has a little more protein.

An easier way is to remember this is that the amount of dry matter in the dry food is about three to four times the amount of dry matter in a moist product. To quickly compare guarantees between a dry and moist food, multiply the guarantees for the moist food by three to four times.