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Dog owners who choose to feed a vegetarian or vegan diet may do so for a variety of reasons. These include animal welfare concerns, a desire to reduce the environmental impact of the foods that they select, or beliefs about what constitutes a healthful diet. Some may also prefer foods that are less highly processed than traditional pet foods or that are produced using human-grade ingredients. Together, these various ingredient categories and processing options have opened up an entirely new set of food options for dog owners.

Nutritionally, dogs are classified as omnivores, which simply means that they consume both animal and plant-based foods and that they are capable of obtaining all of their essential nutrient needs from plant matter. However, we also know that dogs evolved from a predatory meat-eater and that that most dogs display a preference for meaty foods and flavors.

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So, our question for today is:

Can we feed dogs a healthful vegetarian or vegan diet?

Once again, science has some answers!

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Although we know academically that dogs can be fed a nutritionally complete plant-based diet, there is not much research that has examined the quality of vegetarian products for dogs. Recently, researchers at the University of Illinois Department of Animal Sciences examined the protein quality, energy content, and digestibility of a fresh-cooked vegan dog food that was produced using human-grade ingredients. Two studies were conducted and published to report their work.

In Vivo Assay

Using two types of validated tests, the researchers compared protein/amino acid digestibility values and metabolizable energy (ME) values of three dog foods (1). The first two were vegan foods produced by Bramble Pets: BC (pea protein, lentil, & sweet potato) and BR (pea protein, brown rice, & potato). The third, control food, was an extruded dry kibble produced by Blue Buffalo, CT (chicken meal, brown rice, barley). The two Bramble foods were produced with human-grade ingredients and were fresh-frozen (gently-cooked) products. The Blue Buffalo product was produced with pet-grade ingredients and extruded. All three products were formulated to provide complete and balanced nutrition for adult dogs.

Results:

• Protein: The two vegan foods had significantly higher total protein contents when compared with the extruded food on a dry matter basis (34/32 % vs. 27 %).
• Essential Amino Acids: The essential (indispensable) amino acid digestibility values were greater than 80 percent for all three foods and for almost all of the amino acids. These values are considered to be moderately high (but are somewhat lower than those reported previously for fresh-cooked, human grade, animal-based foods (see Human Grade).
• Methionine and Taurine: All three products contained sufficient methionine (taurine precursor) and the two vegan foods contained higher levels of taurine when compared with the kibble. (Note: Taurine was supplemented in all three food formulations).
• Energy (Caloric) Content: Both of the vegan products had higher energy values than the extruded kibble (4.6/4.7 kcal/gm vs. 3.9 kcal/gm).

Conclusions

The assays used in this study found that the two human grade, mildly-cooked vegan dog foods performed very well. The protein, energy and essential (indispensable) amino acid levels met or exceeded AAFCO guidelines and digestibility values for all of the tested nutrients were moderate to high.

These results suggest an expectation that these foods would perform well in feeding trails with dogs – the task of the next study conducted by this group of researchers. (So cool – This is science at its best!!)

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Feeding Study with Dogs

The next important step with the vegan foods was to test their nutritional quality when fed to dogs. The same set of three foods was fed to a group of 11 healthy adult dogs on a rotating basis (i.e. all of the dogs were fed all three foods; see paper for design details). Dogs were fed the food for 28 days. During the last 6 days, blood was collected for serum chemistry and hematology data and feces were collected for fecal scoring, digestibility calculations and measurements of fecal metabolites and microbiota.

Results:

• Food Acceptability: All of the dogs readily consumed all three products and had similar caloric, protein and fat intakes.
• Digestibility: Dry matter digestibility values were moderately high for all three foods (83 – 84 percent) with no significant differences among the products (Note: This differs from earlier studies of fresh-cooked human-grade foods produced with animal-source proteins. In those studies, the fresh-cooked foods had significantly higher digestibility values when compared with kibble).
• Protein: Similarly, protein digestibility was moderately high for all three foods – values of ~ 85 percent. The fresh-cooked vegan foods were similar to, but did not out-perform, the traditional kibble product in terms of protein digestibility.
• Blood Values: All dogs’ hematology and chemistry values were within the standard reference ranges for healthy dogs. Within those ranges, dogs fed the vegan foods had lower cholesterol, triglyceride, platelet and neutrophil values when compared with dogs fed the kibble.
• Stool Quality: Fecal scores were normal in dogs fed all three foods. When consuming the vegan products, dogs had several differences that are generally classified as desirable (lower dry matter, and lower indole/phenol levels), including an increase in fecal microbiome diversity.

Conclusions

The two human-grade, gently cooked, vegan dog foods were well-accepted by dogs, had moderately high digestibility values, maintained health, and resulted in normal feces production. Some changes that might be considered beneficial were observed in blood parameters (reduced cholesterol and triglyceride levels) and in fecal microbiota (increased SCFA, reduced phenol and indole).

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Take Away for Dog Folks

There are three important food characteristics to unpack with this research. These are:

1. Human-Grade Product: I have written about human-grade pet foods often. Prior to this pair of studies, all of the work that has been published has been with meat-based products. Generally, human-grade foods perform better than traditional products produced with pet-grade ingredients, both in biological assay tests and when fed to dogs. (see Human-Grade and New Scoop).
2. Mildly (aka Gently) Cooked Food: A recurrent issue, however, is that the use of human-grade ingredients is almost always confounded by the fact that these products are also less processed. It is difficult, if not impossible, to separate out the contributions of these two attributes (human-grade ingredients and reduced processing) on feeding outcomes. Suffice it to say, at this time, that including human-grade ingredients and reducing the degree of thermal processing lead to improvements in dog food quality.
3. Vegan Food: To my knowledge, these two studies are the first to report an analysis of protein/amino acid quality and feeding results of a human-grade, gently-cooked, vegan dog food. Earlier studies have examined the nutrient content of both commercially-produced and homemade vegan dog foods, and have often found these foods to be nutritionally insufficient. However, the current study not only found that the vegan products were nutritionally complete, but that their protein content was sufficient, amino acids exceeded AAFCO recommendations, and the foods performed very well when fed to dogs.

Taken altogether, this is very good news for owners who are interested in feeding a vegetarian or vegan diet to their dog. While is it important that attention is paid to protein source and quality, the performance of these foods tells us that it is indeed possible to feed a healthful vegan diet.

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A Science Dog Recommendation

If you read The Science Dog books and blog or have taken our courses, you know that we consistently recommend feeding a selection of high quality foods to dogs – both mixing foods together and rotating products. In response to recent research, we also recommend including at least one (or more if possible) less highly processed foods and/or a human-grade product into that mix. The research reported in this essay further informs us that it is safe and nutritious to include a balanced, gently-cooked vegetarian food in a dog’s diet, if that is a value that is important to an owner. However, because these foods have not been tested for long periods of time (as have very few foods, actually), it is still wise to not feed any food, including a vegetarian product, exclusively.

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Happy Feeding!

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Cited Studies:

1. Roberts LJ, Oba PM, Utterback PL, Parsons CM, Swanson KS. Amino acid digestibility and nitrogen-corrected true metabolizable energy of mildly-cooked, human-grade vegan dog foods using the precision-fed cecetomized and conventional rooster assays. Translational Animal Science, 2023; (In Press); 7(1), txad020.
2. Roberts LJ, Oba PM, Swanson KS. Apparent total tract macronutrient digestibility of mildly-cooked, human-grade vegan dog foods and their effects on the blood metabolites and fecal characteristics, microbiota and metabolites of adult dogs.  Journal of animal science, 2023; (In Press); skad093.

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