Is Raw Dog Food More Digestible than Kibble?

One of the most important factors of how nutritious a food is for a dog, is how digestible a diet is. Sadly this information is actually nowhere on the pet food label. In order to get this information you will actually have to contact the dog food company directly – and sad to say – some companies will not actually even give these numbers out to the public as they deem it “proprietary” information.

But what is digestibility?

“Digestibility of a pet food measures the proportion of the nutrients within the food that are available for absorption by the dog.”

Canine and Feline Nutrition, Case 2011

What is a Digestibility Trial?

A digestibility trial looks at the food itself and compares the food going in, with the product that comes out (aka the feces) to see how much of the food is digested by the animal, and how much is able to be utilized by the animal.

This is different from an AAFCO Feeding Trial which measures how the dog responds to being fed a food. A dog food that has low digestibility could pass an AAFCO Feeding Trial if proper adjustments were made.

The process of a digestibility trial is fairly simple.

  1. Food is analyzed in a lab for nutrient content.
  2. Food is fed to a dog for a certain period of time as the sole diet (usually two months). A series of stool samples (or a stool sample) is collected in the last month of the trial.
  3. Stool sample(s) is/are analyzed in a lab for nutrient content.
  4. Nutrient content of the food is compared to nutrient content of the stool to calculate overall digestibility.

Typically companies will collect multiple samples during the trial and give an average final digestibility. This is because digestibility numbers will range over time as the body may need more or less of certain nutrients each day naturally. Most trials collect samples after a one month transition – this is because the microflora within the body takes time to adjust to new food items. So for ideal digestibility numbers most companies will wait to test stools until after a dog has been fed the diet for a certain period of time in order to get the most accurate numbers for digestion long-term.

Why do we need Digestibility Trials on Dog Food?

The problem is – digestibility trials are not required to be done by dog food companies. And without the data from digestibility trials companies cannot make any necessary adjustments to their recipes to make sure they are meeting all your dog’s nutritional needs.

Tjernsbekk 2016

This was shown quite clearly in a 2016 study that looked at the use of three different types of meat meals in dog food – chicken, salmon and lamb (Tjernsbekk 2016). The diets were formulated to AAFCO nutrient standards. However after conducting a digestibility study they found that not only was the lamb diet significantly less digestible than the salmon or chicken, but that because it was less digestible – the diet was deficient in an amino acid (protein) called methionine. Though deficiencies of this amino acid were slight, if compounded over time without supplementing additional taurine nutrient deficiencies could cause heart problems, such as dilated cardiomyopathy.

Thus as consumers we should both ask and advocate for more transparency regarding these digestibility trials, in an ideal situation these trials would be required and the number would be included on every dog food label – right next to the guaranteed analysis. This would also make it easier as a consumer to find diets that are highly nutritious for our dog’s. 

Kibble vs Raw – Which is More Digestible?

There are so many factors that influence that overall digestibility of a diet. Generally speaking researchers have found that animal based products tend to be more digestible for dogs than plant based products in dogs. Certain starches, vegetables and even fruits are more digestible in cooked form than in raw form. They have also found that certain ingredients contain compounds that can inhibit digestion of other compounds. (Case et al 2011)

It is generally accepted that:

  • Less than 75% Dry Matter Digestibility is Poor Digestibility
  • 75% to 82% Dry Matter Digestibility is Moderately Digestible
  • 82% or more Dry Matter Digestibility is Highly Digestible

Kibble Digestibility

According to research the average digestibility for dry dog foods is 81% protein, 85% fat, and 79% carbohydrate (NFE), with an average digestibility of 82%. In a research study looking at the digestibility of eight different dry food diets of different compositions from both the grocery store and boutique stores, they found the overall digestibility ranged between 73% to 88% digestible (Daumas et al 2014).

On average the moderately priced and premium brands were more digestible than grocery store brands. But, there was not a significant difference in digestibility between moderately priced and premium brand digestibility. There was also no correlation between crude protein or fat levels and overall digestibility (Daumas et al 2014) – meaning that simply choosing a dog food that is “higher in protein” or “lower in carbohydrates” will not necessarily mean the food is more digestible.

Daumas et al 2014

In order to provide some references as to digestibility of different brands of kibbled dog food on the market today, I reached out to about a dozens different companies asking them for their digestibility data – and some responded via email to give me those numbers (though I will admit, some companies were less specific than others).

  • Wellness Dog Foods: 78% to 87%
  • Organix: 82 to 84%
  • Instinct Kibble: 80s%*
  • Orijen: 80s%*
  • Fromm: 85%*

*companies gave generalized values rather than exact figures. 

Gently Cooked Dog Food Digestibility

As gently cooked diets are newer options in the dog food manufactured diet space, there are no generalized recognized averages as far as overall digestibility. However there has been some research looking at overall digestibility of gently cooked diets in comparison to kibbled diets.

One study compared a kibbled, gently cooked grain-inclusive and gently cooked grain-free diet. It found that the kibbled diet had an overall digestibility of 87%, the grain-inclusive cooked had an overall digestibility of 90%, and the grain-free cooked had an overall digestibility of 93%. (Algyla 2018). Showing a slightly higher digestibility in the cooked diet than the kibbled diets. However, it should be noted that diet composition between diets was significantly different – bringing into question if the diets were composed in a similar manner – would the digestibility be the same?

Algyla 2018

But what is the digestibility of different gently cooked diets on the market today? I went ahead and contacted several gently cooked dog food brands to see if I could get some digestibility data, these were the brands who responded:

  • Nom Nom Now: 90-94%
  • Pet Plate Beef: 86%
  • Pet Plate Turkey: 93%
  • Honest Kitchen (dehydrated): 86-90%
  • Instinct (canned): 90s%*
  • Just Food For Dogs Venison: 82%
  • Just Food For Dogs Chicken: 94%

*companies gave generalized values rather than exact figures.

Raw Dog Food Digestibility

Similar to the gently cooked category, there are no generally recognized averages for digestibility of raw dog foods. However there is one study of note in dogs that compares kibbled, cooked and raw diets of different compositions, and one study done in cats that compares kibbled, cooked and raw diets of similar compositions.

The first study in dogs found that the overall digestibility of the kibbled diet to be 87%, the overall digestibility of the cooked diets to be 90/93%, and the overall digestibility of the raw diet to be 90%. It should be noted that the overall composition and ingredients within the diets were significantly different – which does make it difficult to draw blanketed conclusions (Algyla 2018).

Algyla 2018

A better study in cats looked at three different beef diets – kibble, cooked and raw – all with similar crude protein values (~50% CP) and found that the cooked and raw diets had higher digestibility than the kibbled diet. However when comparing the cooked and raw diet the differences in digestibility was not significant (Kerr et al 2012).

“Results indicated that cooking a raw meat diet does not alter apparent total tract energy and macronutrient digestibility”

Kerr et al 2012

But of course I did want to get some real-life examples of diets currently on the market on their overall digestibility. Out of the dozen or so raw food companies contacted the following were the only ones who responded back with digestibility information.

  • Primal Freeze Dried Chicken: 94%
  • Primal Frozen Chicken: 95%
  • Primal Frozen Lamb: 93%
  • Instinct Raw Frozen: 90s%*
  • Ziwi Peak Freeze Dried: 90s%*

*companies gave generalized values rather than exact figures.

So which type of dog food is more Digestible?

Overall by looking at the research and by comparing the numbers reported by pet food companies – we can say that the average gently cooked or raw diet is more digestible than the average kibbled diet. However, we do not have evidence that supports the fact that there is a significant difference between cooked and raw diets of similar ingredients and composition at this time. We can also say that raw and gently cooked diets on average seem to be highly digestible, however, since digestibility can range due to ingredients, formulation, and recipe – it’s best to contact the company directly for digestibility information.

Hope you found this comparative research analysis interesting! What do you think about digestibility in dog food? How significant do you think the digestibility differences are between the different types of food?

Til next time my canine health nuts!

RESOURCES:

Algya, Kiley M et al. “Apparent total-tract macronutrient digestibility, serum chemistry, urinalysis, and fecal characteristics, metabolites and microbiota of adult dogs fed extruded, mildly cooked, and raw diets1.” Journal of animal science vol. 96,9 (2018): 3670-3683. doi:10.1093/jas/sky235

Case L, and Daristotle L. “Canine and Feline Nutrition: A Resource for Companion Animal Professionals” Jan 2011.

Daumas, Caroline et al. “Evaluation of eight commercial dog diets.” Journal of nutritional science vol. 3 e63. 30 Dec. 2014, doi:10.1017/jns.2014.65

Kerr KR, Vester Boler BM, Morris CL, Liu KJ, Swanson KS. “Apparent total tract energy and macronutrient digestibility and fecal fermentative end-product concentrations of domestic cats fed extruded, raw beef-based, and cooked beef-based diets”. J Anim Sci. 2012 Feb;90(2):515-22. doi: 10.2527/jas.2010-3266. Epub 2011 Oct 14. PMID: 22003235.

Patrícia M Oba, Pamela L Utterback, Carl M Parsons, Kelly S Swanson, “True nutrient and amino acid digestibility of dog foods made with human-grade ingredients using the precision-fed cecectomized rooster assay”, Translational Animal Science, Volume 4, Issue 1, January 2020, Pages 442–451, https://doi.org/10.1093/tas/txz175

Tjernsbekk MT, Tauson AH, Matthiesen CF, Ahlstrøm Ø. “Protein and amino acid bioavailability of extruded dog food with protein meals of different quality using growing mink as a model.” J Anim Sci. 2016 Sep;94(9):3796-3804. doi: 10.2527/jas.2016-0526. PMID: 27898909.

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