Calculating Pet Food Dry Matter Basis

Pet owners often wonder whether their dog food is high in protein, fat, or carbohydrates- the macro nutrients of the food.  Unfortunately, the answer to these questions is not easily attainable from the dog food label.  To calculate a pet food’s protein, fat, or carb values, the guaranteed analysis on the label must first be converted to a dry matter basis.  This article will demonstrate how to do this.

Let’s start by looking at the typical food label guaranteed (or crude) analysis which displays the relative amounts of the macro nutrients.  Most labels show you the percentages for the following:

• Protein
• Fat
• Fiber
• Moisture

As you can see, there is no mention of the carbohydrate content.  But that doesn’t mean that we can’t determine that component value.

Before we show the calculation, we must take a sidestep and discuss another ingredient that isn’t often listed, Ash.  The ash content in a food is needed to more accurately estimate the carbohydrate content.

What is Ash?

Ash is the inorganic material that remains after organic material is burnt up.  Ash is made up of mineral nutrients like calcium, phosphorous, zinc, iron, etc.   Ash itself is not necessarily bad-- most ash comes from the bone content and minerals additives in a product.  In general, dry pet food is always going to contain ash content while wet food will occasionally have it in smaller amounts.

Ash content is not often displayed on the dog food label.  If it is, you will use that value when doing the carbohydrate calculation.  If the ash content is not explicitly stated on the label, according to “Applied Veterinary Clinical Nutrition”, Andrea J. Fascetti, Sean J. Delaney, you can use an estimate of 2.5% for canned food and 8% for dry food.

Calculating Dry Matter Macronutrient Content of Dog Food

The calculation of the macronutrient content is a simple 2 step process.  The first step is to estimate the percentage of carbohydrates on an as fed basis, and the second step is to convert it to a dry matter basis (which adjusts for water content).  We will use the example label below in our calculations.

Example Dog Food Guaranteed Analysis

Step 1- The protein, fat, carbohydrate, ash and moisture content account for almost 100 percent of the total pre-cooking weight of any dog food.  By subtracting the protein, fat, water and ash percentages from the 100 percent total, you will have an estimate of the total carbohydrate content.  Using our example above:

100-26-16-10-7.5= 40.5% carbohydrates.

Note that the fiber is not included in this calculation because it comes from carbohydrates so it is already a part of the carbohydrate total.

Step 2- Convert to dry matter basis- this step allows you to compare dry food and canned food as it adjusts for water content.  The dry matter calculation is a simple ‘rebasing’ of the nutrient profiles after removing the water content.  To rebase the values, divide each macronutrient percentage by (100-Moisture %).

Using our example above, we rebase by taking the protein, fat, and carb amounts from above and divide by the dry matter (100%-10% moisture = 90% or .9).  Here are the results for the main macronutrients.

Example Dog Food Guaranteed Analysis

The net result of these calculations is that this example food is 45% carbohydrate on a dry matter basis.  Most dog foods have a carbohydrate percentage between 30-70%, with higher values normally associated with lower quality foods that use grains and other low cost fillers to provide a disproportionate amount of the foods energy benefit.  Cat foods are generally higher in protein and lower in carbs because cats are obligate carnivores.  However, far too many cat foods include more carbohydrates than is optimal for the cat’s body.

Here is another example using a canned food.  You will see a marked change in the macronutrient components because canned food has a much larger moisture content than dry food.

Example Dog Food Guaranteed Analysis

Work out the dry matter analysis on your own before checking below!  We gave you some hints by providing the Ash and Carb values already.

Because this food is 76% moisture, the macronutrient values from the above table will need to be rebased by (100%-76%) or 24%.

Example Dog Food Guaranteed Analysis

Visually, look at the difference in a Pie Chart.  First, as reported in the label.

Now after adjusting for moisture:

What a difference!

What does this all mean for my pet?

First of all, check with your vet to make sure your pet does not require a special diet.  Dogs are meant to eat high protein and high fat diets. Cats require meat protein to survive and thrive.  So run a dry matter calculation on your pet’s food, or look it up on our SmartFood site, to see how the protein, fat, and carbs stack up.  If you see a high value for carbs, be wary and consider alternatives (assuming that there is no medical reason for a lower protein/fat diet).

References and further reading:

• http://www.petcarerx.com/c/628/dogs/food-nutrition/ash-in-pet-food-filler-or-nutrient
• “Applied Veterinary Clinical Nutrition“,  edited by Andrea J. Fascetti, Sean J. Delaney