Vegetarian and Vegan diets for dogs

Recently, the concept of feeding vegan or vegetarian diets to dogs has been a hot topic of discussion. With around 3.25% of us in the UK describing ourselves as ‘fully vegan’ (1), it is unsurprising that this lifestyle is now being considered for our pets.

Carnivores or Omnivores?

We all know that dogs originated from wolves (spoiler alert if you didn’t). However, it is a common misconception that dogs have the same digestive capacity as wolves! Thousands of years of selective breeding and adaption to different diets has unsurprisingly had an impact on their digestion.

In comparison to wolves, genetic sequencing has revealed vast differences in fat metabolism and, more notably, starch digestion. Mutations in these genes followed by their contribution to the gene pool played an important role in canine domestication and adapting to starch rich diets (2).

Starch of course is the main form of carbohydrate found in plants. During the agricultural revolution, we saw an increase in the availability of plant-based foods. The result of this is an increase in dietary starch - both for us and our dogs (2). Like all successful organisms, we had to adapt!

Dogs don’t have salivary carbohydrate pre-digestion (unlike us), while their stomach is more acidic than ours (3). Carnivores tend to produce more stomach acid to help with protein digestion and to kill bacteria that can be found in meat. Think of how a dog looks and behaves - they have physical carnivorous traits (e.g. defined canine teeth)(5).

Unlike cats, dogs are not ‘true’ carnivores… although they are still carnivores (4). In other words, dogs are more adapted to eating plant-based materials than cats, but they cannot be classified as true omnivores either! The best way to describe dogs is as carnivores with increased omnivorous digestive capacities.

It should be noted that dietary carbohydrate is not essential for cats or dogs, as they can acquire sufficient energy from amino acids in proteins. However, both can still utilise digestible carbohydrate in feed for energy, more so dogs than cats (3).

On the other hand, what happens when we remove meat?

There is little research investigating how well dogs cope with vegan and vegetarian diets, although some evidence suggests that dogs can survive on vegetarian diets (5). The main problem with feeding dogs plant material is that it can be lower or absent in many essential nutrients that are found in meat (5).

In livestock nutrition (where mainly plant-based diets are fed), ingredients must be frequently analysed for their nutrient content. This is because the composition of crops can be variable, so we must know what the ingredients are providing to formulate nutritionally adequate diets. Commercially available canine vegetarian diets have been investigated, and it was found that often they did not meet the claimed nutrient, vitamin, and mineral content!(5)

Because of the variability of plant-based diets and the lack of certain essential dietary components, these diets should be supplemented to make them nutritionally adequate for dogs. We can add synthetic amino acids, vitamins, and minerals to our heart’s content, but it is important that these diets are balanced and formulated correctly - as with any pet food!

Vitamins

Unlike us, dogs cannot synthesise their own Vitamin D3. This vitamin is non-obtainable from plant-based sources. As animals synthesise it, it is only obtainable from animal sources (e.g. meat, fish, and eggs)(3). Vitamin D2 can still be obtained from plants, but this is less ‘bio-active’ than D3 (7). Vitamin D is essential for the uptake of calcium and phosphorus!

Similarly, vitamin B12 is virtually non-existent in plants. You can obtain B12 from animal products like dairy and eggs, but it must be supplemented in vegan diets (6). This vitamin has various biological functions and is essential in canine health (3).

Minerals

Deficiencies in calcium, phosphorus, zinc, and iron can result when using diets free from animal products.

Calcium is usually supplemented through bone meal (which is not vegetarian friendly!) Often plant phosphorus is in complex with a molecule called phytate (or phytic acid), which is virtually indigestible! The amount of phytate phosphorus is particularly high in cereals, grains and pulses.

Phytate is an ‘anti-nutrient’ that can reduce the bio-availability of calcium, zinc and iron from other food ingredients (11) — think of the phytate molecule as a cage that traps essential minerals! Be sure that plant sources contain available and easily absorbed minerals and nutrients.

Amino acids

Amino acids are the building blocks of proteins. Different species will have different ‘essential’ and ‘non-essential’ amino acids. Non-essential amino acids can be synthesised by the animal, if provided with the correct mix of other amino acids. Essential amino acids cannot be synthesised and therefore must be acquired through dietary sources.

You can obtain most amino acids from plants, but they can be poor sources of some (e.g. methionine, which is essential to dogs)(9). This again increases the necessity for supplementation.

Fatty Acids

Vegetarian diets can be low in n-3 fatty acids such as DHA, which plays a role in healthy brain and nervous system development in young animals. Mammals get DHA from their mother’s milk and good supplemental sources are fish oils (10).

We wean puppies earlier than they would naturally, therefore we need to be mindful of post-weaning nutritional deficiencies that can result from meat-free and vegan diets. These deficiencies include, but are not restricted to, fatty acids.

The take-home message:

Dogs are adapted to eat both meat and plant based foods, while they can survive on vegetarian and vegan diets. Because of the variability and lack of certain nutrients in plant sources, it is more difficult to balance these diets nutritionally. Diets can be balanced though supplementation with careful and accurate formulation. Vegetarian diets are less of a challenge because a dog will still benefit from the addition of non-meat animal material, such as eggs. It is harder to ensure that vegan diets meet the vitamin, mineral, amino acid requirements of your dog.

There is no research into how well dogs cope on long-term meat-free diets. Although they can survive without meat, can they thrive? If diets are correctly balanced, there is no reason they wouldn’t.

Until our knowledge on the matter has grown, treat these diets with caution. Personally, I would avoid feeding vegan diets to puppies all together.

Marco A. Crisci

References

1. Ipsos MORI. (2017). Vegan Society Poll. [online] Available at: https://www.ipsos.com/ipsos-mori/en-uk/vegan-society-poll?language_content_entity=en-uk [Accessed 7 Jun. 2017].

2. Axelsson, E., Ratnakumar, A., Arendt, M., Maqbool, K., Webster, M., Perloski, M., Liberg, O., Arnemo, J., Hedhammar, Å. and Lindblad-Toh, K. (2013). The genomic signature of dog domestication reveals adaptation to a starch-rich diet. Nature, 495(7441), pp.360–364.

3. WALTHAM® pocket book of essential nutrition for cats and dogs. (2009). 1st ed. [ebook] Leicestershire: MARS; WALTHAM® Centre for Pet Nutrition. Available at: https://www.waltham.com/dyn/_assets/_pdfs/waltham-booklets/Essentialcatanddognutritionbookletelectronicversion.pdf [Accessed 7 Jun. 2017].

4. Case, L. (2011). Canine and feline nutrition. 4th ed. Maryland Heights, MO: Mosby.

5. Knight, A. and Leitsberger, M. (2016). Vegetarian versus Meat-Based Diets for Companion Animals. Animals, 6(9), p.57.

6. Phillips, F. (2005). Vegetarian nutrition. Nutrition Bulletin, 30(2), pp.132–167.

7. Arnarson, D. (2017). 7 Nutrients That You Can’t Get From Plant Foods. [online] Authority Nutrition. Available at: https://authoritynutrition.com/7-nutrients-you-cant-get-from-plants/ [Accessed 8 Jun. 2017].

8. Craig, W. J., & Mangels, A. R. (2009). Position of the American Dietetic Association: vegetarian diets. Journal of the American Dietetic Association, 109(7), 1266–1282.

9. Kanakubo, K., Fascetti, A. J., & Larsen, J. A. (2015). Assessment of protein and amino acid concentrations and labeling adequacy of commercial vegetarian diets formulated for dogs and cats. Journal of the American Veterinary Medical Association, 247(4), 385–392.

10. Hill’s Pet Nutrition. (2017). What DHA is and What it Means for Your Pet’s Diet | Hill’s Pet. [online] Available at: http://www.hillspet.com/en/us/pet-care/nutrition-feeding/dha-for-dogs-and-cats [Accessed 7 Jun. 2017].

11. Davies, N. (1982). Effects of Phytic Acid on Mineral Availability. In: G. Vahouny and D. Kritchevsky, ed., Dietary Fiber in Health and Disease. New York: Plenum Press, pp.105–116.