As Fed, Dry Matter, Calories
As fed ("wet weight") values include the water content of the food which makes it impossible to compare foods with different moisture levels. "As fed" means just what it sounds like - the composition of the food as it comes out of the can or the bag. Dry food cannot be compared with canned food when using these values.
Dry matter basis (DMB) removes the water from the equation. When foods are considered on a DMB, they can be compared with one another - regardless of the water content. In other words, a canned food with 78% water can now be compared with a dry food that contains 10% water.
Here is an example of DMB calculation to show you why you can't compare, for example, the protein content of a canned food with the protein content of a dry food:
Let's say you have a can that states a "minimum of 10% protein" and a "maximum of 78% water". As discussed below, these values are inherently unreliable since they are only minimums and maximums - not set values - but let's assume that we have not called the company for actual measured values and the information on the can is all we have to go on.
If you subtract 78% (water) from 100%, that leaves you with 22% dry matter - which includes protein, fat, carbohydrates, ash, and fiber.
Take the 10% minimum protein and divide it by 22%. This gives you a value of 45% minimum protein on a DMB.
Now let's say that you have a dry food that lists "protein 30% minimum" and "moisture 10% maximum". At first glance - before DMB is calculated - it appears that the dry food has more protein (at 30% as fed) than the canned food (at 10% as fed).
However, when you consider that the dry food only has 10% water and you subtract that from 100%, you find that you have 90% dry matter.
Now divide your 30% minimum protein amount by 90% and you end up with 33% protein on a dry matter basis which is less than the 45% DMB protein found in the canned food.
Calories (metabolizable energy) This is the most accurate way to compare foods with one another. This measurement disregards any part of the food that does not provide calories such as water, ash, or fiber. It only considers the fact that calories are derived from the protein, fat, and carbohydrate fraction of the food and nothing else.
As mentioned many times on this website, a valuable resource for information regarding the composition of many commercial foods can be found on Janet and Binky's chart. However, it can be an extremely frustrating task to try and get actual measured values out of a company but fortunately, Janet is a stickler for detail and her chart only includes food for which she has obtained the more accurate actual measured values versus the vague guaranteed analysis numbers on the can.
That said, and as noted above in the Contacting Pet Food Companies section, please call the companies in question if you desire the most current information on any food that you are feeding. Formulations can change frequently and it would be impossible to keep the chart completely current.
You will notice that Janet lists the protein, fat, and carbohydrate values in terms of 'percentage of calories' from each component (metabolizable energy values) versus listing them as dry matter basis or as fed weights. All 3 columns on her chart add up to 100%. If you are interested in how Janet computes the 'calories from' values from the wet or dry weights, please see her FAQ page or this section above.
The 'wet weight' or 'as fed' values are what you see on the side of the can under 'guaranteed analysis'. This information is not very useful since, by definition, minimums and maximums are inaccurate.
