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Digestibility of dog food (& quality ingredients) is an important factor in nutrition

dog eating food

dog eating food Just as palatability is an important factor in making dog food attractive to dogs, digestibility is more so. Digestibility is a direct measure of the proportion of nutrients in the food that are available for absorption (use) by your dog.

Carbohydrates (commonly grain in pellets and wet dog food) are useful for strengthening the intestine, however if most of a food is passed through a dogs systems undigested, the dogs body will work overtime trying to digest the food, flatulence can occur, malnutrition, or over eating in an attempt to gain sufficient nutrients. This article looks at the difference between low and high quality manufactured dog food and the digestibility of different dog food sources.

Note that while AAFCO is responsible for setting the standards of nutrients required in dog food for it to achieve a “complete and balanced” rating, it DOES NOT require that companies determine or state the digestibility of their dog foods !!


There are two main methods.

The most accurate way is for the company to perform laboratory analysis of the finished product. The ‘guaranteed analysis panel’ of the pet food label is made from proximate analysis results. AFFCO requires that the panel reports only the minimum and maximum levels of a select group of nutrients.

Proximate analysis uses test that show the percentage of moisture;  crude protein, crude fat, ash (minerals)  and fibre  are contained in the food. Nitrogen free extract (NFE) is a rough estimate of the soluble carbohydrate fraction of the food.

The second method to find nutrient content is a calculation of the average nutrient content of the foods ingredients using values reported in standard tables, rather than using calculations based on the actual food ingredients. This is the cheaper less accurate way, but manufacturers can use either method. One example of issues with this method is in the method of calculation of the percentage of protein in corn and soybean from tables. This is because as yields of these crops have increased (in the US) the average protein percentages have decreased, and this is not always reflected in the standard tables.

A real example of the issue with these estimates is the value for Corn taken from different locations and states in the US. from 200 areas. The % of protein was found to vary between 5.97% and 10.25% with an average of 7.87%. Note protein is a very important part of a dogs diet.

Another issue of using tables to calculate nutrient value is that it does not reflect the actual quality of the ingredients used.  This goes directly to defining the availability of nutrients in the pet food for the dog. Processing and storage of a pet food can further severely affect the quality of the dog food and nutrient availability.

HOW to calculate dog food digestibility

Digestibility is usually preformed by feeding trials. Dog food is fed into a number of dogs and their stools are analysed to see what nutrients come out. The difference between input and output is the availability of nutrients or digestibility.

Digestibility coefficients show the difference between high and low quality food sources for dogs. These coefficients also called APPARENT coefficients because by-products of metabolic processes in the animals must also be subtracted from the ‘output’. True digestibility factors take account of metabolic processes and usually give a more realistic value of protein available for use by the dog.

An example of digestibility coefficients:  If food contains 28% protein but its protein digestibility is 70% then only 28 x 0.7 = 19.6% is digestible protein. A low digestible dog food means a dog will have to consume a higher volume of food.  Digestibility also has a large affect on faecal volume and form and defecation frequency.

Metabolisation Energy (ME) is also an important factor in selecting a diet but is out of the scope of this report. ME indicates the amount of energy in the pet food that is available to the animal for use. While digestibility energy (DE) measures the amount of energy that is absorbed across the intestine wall. ME measures digestibility AND the losses of energy in the urine and through expired gas (flatulence) which is a by-product of poor digestibility.

What digestibility means to your dog

A low digestible pet food has a high number of ingredients that cannot be digested by the enzyme of the dog’s gastrointestinal tract. These ingredients pass through the large intestine and are then fermented by the colonic bacteria. Excessive fermentation causes excess gas (flatulence), loose stools or diarrhoea.

A side-effect of this is that more food needs to be eaten to achieve sufficient nutrient uptake. Besides massive stools (often seen with a pellet fed dog) the passage of the food through the intestine increases which further increases poor digestibility, ash, phytate, and poor quality protein.

“IN GENERAL, DOGS AND CATS DIGEST FOODS OF ANIMAL ORIGIN BETTER THAN THOSE OF PLANT ORIGIN” The primary reason is plants have: lignin, cellulose, and other non fermentable fibres. Note pet food that contains poor quality animals ingredients such as skin, hair, feather and connective tissue also cause poor digestibility.


The cat is a strict carnivore, while the dog can tolerate some plant material. This means that the dog in general has higher digestibility coefficients for the same pet food (containing grain and vegetable matter) than cats do.


The text that this information is taken from compares many different pet foods but does not disclose brands, merely compares label A with label B. It admits that there is a vast variability between quality of dog foods, and because of digestibility issues, that the simple AAFCO required labels tell very little about the suitability of each manufactured dog food.

The reference text  also mentions raw food diets and that “there is no objective date to support or refute any of the claims” of raw foods superiority over manufactured dog food.

It seems that besides the nutrient make up of raw meat (that may or may not be superior, ie meat proteins V vegetable proteins etc), that the major claim against manufactured dog food can be the quality of ingredients and the processing storage that can destroy nutrients. Manufactured dog food also is mostly created from non meat products.

While meat products have a much higher digestibility than plant products, the raw ingredients also cost more (the primary reason meat is so little in manufactured dog food). The text mentions that meat handling safety concerns must also be addressed but also points to issues that a home-made diet may not reach the AAFCO standard for “complete and balanced” dog foods.

I was surprised by this as I thought that the text may make a stand for raw meat diets, considering their better digestibility, appropriate levels of palatability, no additives or colouring etc and a few other benefits, however it does primarily base its views on comparisons of nutrient levels as dictated by the AAFCO requirements.

This means that you either believe the AAFCO levels are created purely based on what the animals need and by rigorous infallible testing, or you believe that nature got it right with dogs in the wild eating mainly meat.  You will also need to suspend disbelief that AAFCO have not been influenced by the two major pet food companies that control the vast majority of the market, globally.


Article by Bruce Dwyer. If you wish to use any of this information please refer to the article as a reference and provide a link to our WEBSITE.

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