It can be difficult to compare dry dog foods to canned dog foods to raw diets as you cannot directly compare the protein and fat contents due to the differing levels of moisture in each of these different forms of dog food. To be able to compare dog foods directly, we need to compare the analysis of each based on ‘dry matter’ i.e. comparing them all as having no water.
This can be the hard part. All pet foods have different levels of moisture. Canned foods can have up to 80% moisture whereas some dry foods can have as little as 6%. This is important for two reasons. The first is that the food is priced by the pound, and when you buy dog food that is 80% moisture, you get 20% food and the rest is water. So the amount of food your pet consumes is small and expensive. The second reason for understanding percent moisture is to help you compare crude protein and fat between brands and between canned and dry. The listings on the label are for the food as it is, not as it would be on a dry matter basis. So, without converting both brands of food to a dry matter basis, you will not be able to compare them accurately. Fortunately, the conversion is not complicated.
If a dry dog food has 10% moisture, we know that it has 90% dry matter. So we look at the label to check the protein level and see that reads 20%. Next we divide the 20% protein by the 90% dry matter and we get 22%, (20/90 x 100 = 22%) which is the amount of protein on a dry matter basis. Does this make sense so far? Good.
Now let us compare this to canned food that has 80% moisture content. We know that with80% moisture we have 20% dry matter. The label shows us that the food has 5% protein. So we take the 5% and divide it by the 20% (dry matter) and mulitply by 100 to give us 25% protein as dry matter (5/20 x 100 = 25%) So the canned food has more protein per pound on a dry matter basis than the dry food.
We can do similar calculations to compare fat, fibre etc.
The same calculation can be applied to raw diets assuming that you know the protein and fat contents of the ingredients and the moisture content.
All too often, I hear people stating that canned or try dog food is lower protein than dry dog foods; as you can see, this is not necessarily the case. The same is often said of raw diets, but many of these actually work out as 40-50% protein calculated on a dry matter basis.
So remember, if you are trying to compare protein levels of different types of food, you must look at them as dry matter content to avoid the misleading difference due to differing moisture contents.