December 17, 2012
You are at your local pet food store, comparing the labels of one food after another, trying to make sense of it all. When comparing nutrient values, you likely will have only the Guaranteed Analysis, as listed on the package, to go by. This is true whether you are comparing foods for cats, dogs, dry kibble or canned, dehydrated or freeze dried. This Guaranteed Analysis is mandated by federal and state regulations, requiring that a proper list of certain nutrient values be listed on the product package.
Many states have adopted regulations for pet food labeling according to AAFCO (Association of American Feed Control Officials) standards. A common minimum state requirement is for a label so show the minimum percentages of crude protein and crude fat and the maximum percentages of crude fiber and moisture. (The term “crude” refers to the method of testing the product, not the quality of the nutrient itself.) Some companies will also include other nutrients as well, such as taurine – for cat foods- or calcium, phosphorous, sodium and magnesium as is seen on our packages. You may see other ingredients listed, too, such as ash or linoleic acid on some pet food labels. For more information, many pet food companies will also provide complete Nutrient Profiles for their foods on their websites.
What tends to cause confusion is that this Guaranteed Analysis is based on an “as fed” or “as is” basis. This refers to the food as it is, straight out of the bag or can, or box in the case of the honest kitchen. This works fine if you are comparing one bag of kibble to the next. But, if you are attempting to compare one type of food to another, such as a canned food to a dry kibble or dehydrated diet, these figures will not be of much help at a glance. The reason is because the relative moisture content of the foods has not been taken into account.
In order to compare these foods on an equal basis, you must consider the amount of moisture and remove this from the equation. The good news is that is simple to do!
To compare one food to another, you want to do so using the Dry Matter (DM) basis. First subtract the listed percentage of moisture from 100% to find the total percentage of dry matter. Using the canned cat food example below, 100-78 = 22% dry matter. Then, in order to find the total percentage of protein on a dry matter basis, divide the percentage of crude protein (11%) by the percentage of dry matter (22%): 11/22 = .50 Then multiply this by 100 to give you your total percentage of protein on a dry matter basis. It would look like this:
A can of cat food:
Crude Protein (min) 11 %
Crude Fat (min) 6 %
Crude Fiber (max) 1.5 %
Moisture (max) 78 %
100-78 (moisture content) = 25% dry matter
11 /22 = .50
.50 x 100 = 50% total protein on a dry matter basis. Notice how different this is than the crude protein value of just 11%.
A box of Prowl lists a moisture content of 4.2% maximum and minimum crude protein of 35%.
Protein, 35% min
Fat, 29.5% min
Fiber, 2.38% max
Moisture, 5.2% max
100-5.2% = 94.8% dry matter
35/94.8 = .369
.37 x 100 = 37% protein on a dry matter basis.
And on a bag of dry cat kibble:
Crude Protein (Min) 38.0%
Crude Fat (Min) 13.0%
Crude Fiber (Max) 6.0%
Moisture (Max) 12.0%
100-12% = 88 % dry matter
38/88 = .43
.43 x 100 = 43% total protein on a dry matter basis.
So, if you were only comparing the relative protein contents of each food, at a a glance, without doing these calculations first, it would appear that the kibble contained the most protein. But, as you can see, on and equal (DM) basis, the canned food actually contains the highest amount of protein in this comparison. You can use this simple formula to compare the fat or other nutrients, too.
For more information about guaranteed analysis, AAFCO and other pet food labeling topics, please see the following links: