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Value Judgment (Dry Matter Values)

A few years ago, when my veterinarian recommended that I switch one of my cat’s foods to one that had a certain level of protein levels. That’s when I learned that comparing the Guaranteed Analysis numbers on nutrient panels was not enough for me to properly compare multiple foods.

Comparing a package of dry food that says it’s 23% protein and a can of wet food that says it’s 10%protein, you might mistakenly think that the dry kibble is the lower protein food. But that’s incorrect! Once you do a simple calculation and compare the two foods on equal terms, you’ll see that the moist food is actually almost twice as high in protein as the dry food! Ack!

guar-anal-both-moist-n-dryguar-anal-as-fed-both-moist-n-dry
It’s almost impossible to accurately compare different pet foods without converting their nutrient measurements to “dry matter basis”. That’s because nutrient contents on the Guaranteed Analysis panel printed on food packages are listed on an “as fed” or “as is” basis. That’s is, wet foods list percentages with water content calculated in and dry foods list percentages without moisture taken into account. Yet water content can make a huge difference in how you interpret nutrient contents.

math-difficulty-EinsteinDoing the math

(Pssst… There’s an automated calculator at http://fnae.org/dmb.html if you want to avoid doing the math.)

Calculating a food’s nutrients to dry matter basis is absolutely critical when you want to compare different types of cat or dog food: dry kibble, wet canned or pouched, raw dehydrated, or frozen raw. The FDA website even states “To make meaningful comparisons of nutrient levels between a canned and dry product, they should be expressed on the same moisture basis.”

  1. Look at the “Guaranteed Analysis” on a label. (Eg: 8.5% protein and 78% moisture)
  2. Subtract the moisture percentage from 100. (Eg: 100 – 78 = 22)
  3. With the resulting figure, divide it into the crude protein figure. (Eg: 22 ÷ 8.5 = 38.5)
  4. The total is the dry matter value. (Eg: 38.5% protein)

For example

Let’s look at an example to compare protein amounts in two different foods. Here are the Guaranteed Analysis statements for each food:

guar-anal-as-fed-moistguar-anal-as-fed-dry
This canned food contains 40% protein on a dry matter basis – way more than the 10% listed in the Guaranteed Analysis.

guar-anal-both-g-a-n-as-fed-moist

Here’s the math for converting the wet food’s protein content to its dry matter basis:

  1. Subtract the amount of water (75) from 100 to get the dry matter content: 100 – 75 = 25.
  2. Divide the protein amount (10) by the total amount of dry matter (25): 10 ÷ 25 = .4
  3. Multiply the result by 100: .4 × 100 = 40.

guar-anal-both-g-a-n-as-fed-dry

Now, let’s convert the dry kibble’s protein content for comparison:

  1. Subtract the amount of water (10) from 100 to get the dry matter content: 100 – 10 = 90.
  2. Divide the protein amount (23) by the total amount of dry matter (90): 23 ÷ 90 = .26
  3. Multiply the result by 100: 26 × 100 = 26.

As you see, if I simply look at the Guaranteed Analysis of both foods, it looks like the kibble has more protein. But that’s far off-target. Here’s a side-by-side comparison of these foods:

guar-anal-both-moist-n-dryguar-anal-as-fed-both-moist-n-dry
How do I know how much food to feed my pet?

Once you’ve chosen a new food, you can begin figuring out how much to give your dog or cat. This takes some trial and error because the feeding directions printed on food packages are merely rough guidelines for us to use as a starting point.

Veterinary professionals are well aware of this. In fact, the National Research Council’s Nutrient Requirements of Cats and Dogs clearly states “the energy requirements of an individual dog cannot be more than an educated guess.” There are many factors that affect how much of a particular food a pet needs, including breed, temperament, age, activity level, and reproductive status. Even pets who are born in the same litter, from the same parents, living in the same house, and getting the same amount of exercise can have food needs that vary as much as 50%.

So when deciding how much of a certain food to offer your pets in order to maintain their ideal weight, start by offering the amount suggested on the package, then increase or cut back as needed.

Work with your vet to talk about the guidelines they recommend for your individual pet. They’ll take into account all the important factors.

(Note: Nonexclusive use of this article has been granted to other pet industry organizations but Kari Kells retains copyright.)

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