Dr Arielle Griffiths BVSc MRCVS
Aren’t dogs carnivores with the dentition to eat meat?
Dogs are opportunist omnivores belonging to the Order Carnivora
Carnivorous Grey Wolves belong to Order Carnivora as well as Herbivorous Panda Bears
Insectivorous Aardwolf living off 2 species of termites belong to Order Carnivora with a very similar dentition to a domestic dog.
Not only has dentition changed but so too has the genome of domestic dog adapted to digest starches compared to a grey wolf. Published studies identify mutations in key genes and provide functional support for an increased starch digestion in domestic dogs relative to wolves. 
Domestic dogs require 50% of their energy to come from carbohydrates whereas wolves need 1.5% of their diet to be carbohydrates.
Studies shown from findings of 36 dog bones buried outside Barcelona, that they lived during Bronze Age and would have been used by man during this period of growth in agriculture to guard crops and livestock. 
Published Research shows that Bronze Age dogs ate very little meat! The fascinating study shows that dogs living around 3000 years ago in what is now Spain, were instead fed cereals and grains, such as millet, by their owners.
“Although the diet may reflect the fact that meat was relatively scarce among human societies at the time, feeding dogs with cereals could have been advantageous… It may have been a way to ensure the dogs had plenty of energy for the strenuous work of herding and guarding livestock….. It was also quicker for them to eat grains and continue their work as guard dogs.”
Silvia Albizuri at the University of Barcelona in Spain 
Why do people choose to feed their dogs a vegan/vegetarian diet?
However, the environmental impact of feeding animal proteins and awareness of the links between health and diet also play a part. Eating a vegan diet and feeding our pets a vegan diet could be the “single biggest way” to reduce your environmental impact on earth as not just greenhouse gases, but global acidification, land use and water use are all reduced. 
Continued humanisation of pets sees owners wanting to choose human-grade ingredients for their pets. Love of one animal translates to not wanting to feed them another animal. Use of human grade meats competes with the human food system and means more animals slaughtered as less use of by-products.
Vegan owners want to choose similar ingredients to what they are eating.
Religious reasons such as Hindu that cannot have meat in home and only choosing to have a pet if can feed it plant-based.
Only diet that can be tolerated by dogs with meat or chicken or fish allergies and intolerances as is a pure novel protein source that excludes all main foods associated with adverse reactions in dogs and cats. 
Final reason for the choice is sustainability with owners aware that the carbon footprint of their dog is equivalent to that of driving a family car over a year if small dog fed a meat-based diet.
For owners wanting to reduce their pet’s carbon paw print, the most effective way to do this is to change to a vegetarian or vegan diet . Clark and Tilman (2017)  agree that plant-based foods have the lowest environmental impact.
What studies have been done showing the safety of these diets?
More published studies done on vegan/vegetarian pet foods than any other type of pet food, especially in recent years with continued growth and interest in this field and a sense of urgency for sustainability reasons.
Prof Andrew Knight and colleagues (Huang E, Rai N, Brown H) published a groundbreaking research paper on the 13th of April 2022 that stated from the findings of 2639 dogs, that “the pooled evidence to date indicates that the healthiest and least hazardous dietary choices for dogs, are nutritionally sound vegan diets.” 
This was followed by similar findings by Dr Sarah Dodd and Colleagues in North America with her studies showing that dogs on a nutritionally complete vegan dog food diet could live up to 18 months longer than a dog fed a meat-based diet! 
This publication and that of Prof Knight drew widespread interest and was critiqued by scientists and vets from Mexico and the University of Adelaide as the studies showed bias with results taken from vegan dog owners. However, their peer review of these papers in January 2023 they had to admit from all the published science that –
Domínguez-Oliva et al. (2023) concluded, “there was no overwhelming evidence of adverse effects arising from use of [vegan pet food] and there was some evidence of benefits”. 
Another recent study (April 23) from the University of Illinois the effect of feeding two mildly cooked vegan diets and an extruded chicken-based diet to twelve beagles. All three diets had a macronutrient digestibility of over 80%. The vegan diets had a higher fat digestibility but lower organic matter digestibility, lower levels of circulating fats in the blood (cholesterol and triglycerides) and lower levels of phenols and indoles (chemicals that make faeces smell) than the meat-based diet. 
Prof Swanson who led the study concluded that – “One thing to remember is that animals don’t have ingredient requirements, they have nutrient requirements. As long as they’re consuming the essential nutrients in the correct amounts and ratios, dogs can be vegan, vegetarian, or meat-eaters.” 
Another study  looked at dogs’ health over 12 months. The dogs were fed on a meat-free diet based on pea protein. It was a small-scale study of 15 healthy dogs that assessed complete blood count, blood chemistry, cardiac biomarkers, plasma amino acids, and serum vitamin concentrations. All dogs remained healthy.
Interestingly, high-legume diets, especially those with peas, have recently been criticised in the US due to a possible link between grain-free, high-legume-based diets and the heart condition dilated cardiomyopathy (DCM). One of the cardiac markers assessed when looking for DCM is Cardiac troponin I (cTnI). Troponin proteins only enter the bloodstream when there is heart muscle damage. In this study, three dogs had slightly increased levels of cTnI (when fed on meat-based diets) compared with only one dog fed a vegan diet at the end of the study. None of the figures were classed as significantly different. This study has not been peer-reviewed.
Master’s student Lukas Kiemer chose to study – ‘The vegan diet and its effects on the dog’s health’. In his study the nutritional adequacy of a vegan diet was determined by analysis of blood samples from 40 dogs, 20 of which were fed a 100% plant-based vegan diet for an average of 2.15 years, and a control group of 20 were fed a meat-based diet. The results showed the same number of surpluses in both groups; however, the vegan group had only two nutritional deficiencies compared to 11 in the meat fed group. 
How to get a vegan diet balanced
Vegan dog food diets need careful formulation to avoid deficiencies in taurine, methionine, lysine and tryptophan. Unlike cats, dogs can synthesise taurine, but they require methionine and cysteine from their diet to do this. Manufacturers of complete vegan diets will use several sources of plant proteins to obtain all essential amino acids and add additional synthetic amino acids to top up the formulation. This is especially important with methionine, taurine and l-carnitine for heart health in all properly formulated vegan dog food diets.
Most of the diets will use pea protein or soya protein as a main protein source and both contain lectins or anti-nutrients so even higher levels of methionine and taurine need to be added. Certain breeds such as Newfoundlands and Golden Retrievers have a higher requirement of Taurine ,
Plant-based proteins, if processed correctly, can be very digestible. Vegetable-based diets can match or even exceed nutrient digestibility compared to meat-based diets  with comparable palatability too as shown by a study of 4060 dog and cat owners in 2021 by Prof Knight .
All pet food manufacturers in the UK must follow EU FEDIAF guidelines, to have the correct addition of Vit D3 (from Algae or lichen if a truly vegan diet), otherwise from lanolin (cholecalciferol from sheep wool) if vegetarian. Adequate Calcium, Phosphorus, Zinc, Iron, Iodine and Vitamin B’s also need to be added. Omega 3 DHA and EPA better sourced from Algae oil (where fish obtain their Omegas) rather than from flaxseed containing ALA. The conversion of ALA in dogs to DHA and EPA does not occur efficiently in dogs (and in some humans). 
Health Benefits of plant-based dog foods
Dogs with animal protein intolerances still react to hydrolysed protein diets and feeding a vegan diet to sensitive dogs ensures complete compliance with every treat or even medication fed checked for animal-based ingredients (such as gelatine capsules still causing reactions in dogs with beef intolerance as same DNA).
Use of pure ingredients such as marine algae for Omega 3 instead of fish removes the concerns about high arsenic levels seen in cats or dogs on a fish-based diet. Fish is not a species appropriate diet for either dogs or cats that are land mammals by origin. No concern of bioaccumulation of heavy metals that accumulate in livers/kidneys of fish and feedlot animals and these tend to be components of meat-based pet food diets. 
The gut health is naturally enhanced in dogs with the addition of natural prebiotic fibres in the food. This has been shown to have a positive effect on skin and overall health with 70% of a dog’s immunity in the gut.
Prof Knight talking at London Vet Show
What is available in the UK and what of the future of sustainable plant-based feeding?
Vegan dog food has been around since the 80’s with start of V-Dog, then Benevo in 2003 so not a new concept. Both high wheat content so not ideal for dogs with allergic skin conditions. Explosion of options for owners in plant-based pet food sector. Main growth is in independent companies with veterinary formulated dry food diets such as Omni, Noochy Poochy, Solo Vegetal (imported as dermatology diet by Dr Sue Paterson), and also growth in ethical brands such as Hownd tinned and dry, The Pack tinned and oven-baked, and DoGood fresh foods.
Growth from corporate brands such as Lily’s Kitchen Vegan Stew tinned and Pets At Home Wainwright’s plant-based tinned and dry foods.
New plant-based pet food companies appearing almost monthly so fastest growth in any pet food sector which is enormously encouraging for the health of our pets and our planet.
- Maria Lahtinen, January 2021, Excess protein enabled dog domestication during severe Ice Age winters
- Wang et al, May 2103, The genomics of selection in dogs and the parallel evolution between dogs and humans
- Erik Axelsson, January 2013, The genomic signature of dog domestication reveals adaptation to a starch-rich diet
- Silvia Albizuri, March 2021, Dogs that Ate Plants: Changes in the Canine Diet During the Late Bronze Age and the First Iron Age in the Northeast Iberian Peninsula
- Dodd December 2022, Owner perception of health of North American dogs fed meat- or plant-based diets
- Knight, A. & Leitsberger, M. 2016, “Vegetarian versus Meat-Based Diets for Companion Animals”, Animals (Basel), vol. 6, no. 9, pp. 57.
- Poore June 2018, Reducing food’s environmental impacts through producers and consumers
- Philip Roudebush DVM, 2013, Veterinary Dermatology.
- MARTENS, P., S.U., B. & DEBLOMME, S. 2019, “The Ecological Paw Print of Companion Dogs and Cats”, Bioscience, vol. 69, no. 6, pp. 467-474
- Clark, M. & Tilman, D. 2017, “Comparative analysis of environmental impacts of agricultural production systems, agricultural input efficiency, and food choice”, Environmental research letters, vol. 12, no. 6, pp. 64016.
- Knight and Huang et al April 23, Vegan versus meat-based dog food: Guardian-reported indicators of health, Plos 1
- Domínguez-Oliva, A., Mota-Rojas, D., Semendric, I. & Whittaker, A.L. 2023, “The Impact of Vegan Diets on Indicators of Health in Dogs and Cats: A Systematic Review”, Veterinary sciences, vol. 10, no. 1, pp. 52.
- Swanson, K.S., Carter, R.A., Yount, T.P., Aretz, J. & Buff, P.R. 2013, “Nutritional sustainability of pet foods”, Advances in nutrition (Bethesda, Md.), vol. 4, no. 2, pp. 141-150.
- Linde, A., Lahiff, M., Krantz A., Sharp, N., Theros T., Melgarejo, T. (2023).’Domestic dogs maintain positive clinical, nutritional, and haematological health outcomes when fed a commercial plant-based diet for a year’. News of Science, 12 Mar, 618, available: https://link-gale-com.ezproxy.lib.gla.ac.uk/apps/doc/A739642456/AONE?u=glasuni&sid=summon&xid=50fa4b09 [accessed 17 Mar 2023].
- Lukas Kiemer, Master’s Thesis, Integrated Studies of Veterinary Medicine, “Vegan diet and its effect on the dog’s health”
- Peng Li, Feb 2023, Amino acid nutrition and metabolism in domestic cats and dogs
- Clapper, G.M., Grieshop, C.M., Merchen, N.R., Russett, J.C., Brent, J.L., Jr & Fahey, G.C., Jr 2001, “Ileal and total tract nutrient digestibilities and fecal characteristics of dogs as affected by soybean protein inclusion in dry, extruded diets”, Journal of animal science, vol. 79, no. 6, pp. 1523-1532.
- Andrew Knight Plos One June 16th 2021, Vegan versus meat-based pet foods: Owner-reported palatability behaviours and implications for canine and feline welfare
- FEDIAF: https://europeanpetfood.org/wp-content/uploads/2022/03/Updated-Nutritional-Guidelines.pdf
- Katja Stoeckel 2011, Fatty acid patterns of dog erythrocyte membranes after feeding of a fish-oil based DHA-rich supplement with a base diet low in n-3 fatty acids versus a diet containing added n-3 fatty acids
- Bampidis V.A. et al./Scientific Papers: Animal Science and Biotechnologies, 2013, 46 (1), Arsenic, Cadmium, Lead and Mercury as Undesirable Substances in Animal Feeds