According to The Vegan Society (2020) veganism is defined as;
‘A philosophy and way of living which seeks to exclude all forms of exploitation of, and cruelty to, animals for food, clothing or any other purpose.’
There has been an exponential rise in the number of people living a vegan lifestyle; research conducted by The Vegan Society discovered that in 2014, 150 000 (0.25%) of the UK population identified as vegan, quadrupling to 600 000 (1.16%) in 2019 (Ipsos MORI, 2016 and 2019). Social media campaigns such as ‘Veganuary’ and ‘Meat Free Mondays’ may have influenced the popularity of a meatfree lifestyle; in 2020, 402 206 people signed up to Veganuary (Veganuary UK, 2020). Data collected annually from the British Social Attitudes (BSA) surveys have noted an overall decline in the consumption of meat and dairy products since 2012, with 29% of respondents having reduced their overall meat consumption. The most common reasons cited for adopting a meat-free lifestyle include: health benefits; taste; value for money; the environmental impact of meat farming; and animal welfare (Richardson et al, 1993; Veganuary UK, 2020).
Animal welfare is often cited as one of the main reasons for adopting a meat-free diet; pet owners have been found to have higher empathy towards animals (Paul, 2000; Taylor and Signal, 2005), and those who own pets are more likely to adopt a vegetarian (6.25%) or vegan (5.8%) lifestyle when compared with non-pet owners (Dodd et al, 2019).
For vegan pet owners a moral dilemma occurs between following their own ideology of excluding all animal exploitation versus exploiting production animals and feeding them to their carnivorous pets, begging the question ‘Are those who follow a vegan lifestyle likely to make their carnivorous pets follow a vegan lifestyle too?’
Trends in pet food often reflects trends in human nutrition; many pet owners anthropomorphise their pets which may explain the increase in demand for commercially produced vegan pet diets as well as serving as a resolution to their moral feeding dilemma. When asked why they chose to feed their pet a meat-free diet, owners often cited the same ethical reasons why they adopt a meat-free lifestyle themselves (Wakefield et al, 2006).
Vegan diet composition and associated diet-induced disorders
Physiologically, dogs and (more critically) cats are carnivores throwing into question the nutritional suitability of vegan pet food. Governing bodies such as the Pet Food Manufactures Association (PFMA), the European Pet Food Federation (FEDIAF) and the Association of American Feed Control Officials (AAFCO) have formulated guidelines detailing the minimum and maximum nutrient levels in commercial pet food to ensure adequate and safe nutrition. The guidelines are peer-reviewed by veterinary nutritionists throughout America and Europe and are regularly updated based on the latest evidence-based medicine. Complete pet food is legally defined as pet food that has sufficient nutrients required for a daily portion (FEDIAF, 2020). Table 1 details the required ingredients for a pet food to be classed as complete.
Table 1. Required nutrients for a nutritionally complete pet food diet
| Major nutrients | Fatty acids | Amino acids | Minerals | Vitamins | Vitamin-like substances |
|---|---|---|---|---|---|
| Protein | Linoleic acid | Arginine | Calcium | Vitamin A | Taurine (cats) |
| Fat | Alpha-linolenic acid | Cystine | Sodium | Vitamin D | Choline |
| Arachidonic acid (cats) | Histidine | Chloride | Vitamin E | ||
| Eicosapentaenoic acid (EPA) | Isoleucine | Manganese | Vitamin B1 (Thiamine) | ||
| Docosahexaenoic acid (DHA) | Phenylalanine | Phosphorus | Vitamin B2 (Riboflavin) | ||
| Tyrosine | Copper | Vitamin B5 (Pantothenic acid) | |||
| Threonine | Magnesium | Vitamin B3 (Niacin) | |||
| Lysine | Zinc | Vitamin B6 (Pyridoxine) | |||
| Tryptophan | Potassium | Vitamin B7 (Biotin) | |||
| Leucine | Iron | Vitamin B12 (Cyanocobalamin) | |||
| Methionine | Iodine | Vitamin B9 (Folic acid) | |||
| Valine | Selenium | Vitamin K |
Zafalon et al (2020) conducted a study to evaluate the nutritional composition of all vegan pet foods available on the Brazilian market (n=4) and compare the results with the FEDIAF and AAFCO recommendations. All diets (one for felines, three for canine) met the minimum levels recommended of macronutrients (fat, protein and carbohydrates). However, all foods analysed had one or more micronutrient below recommended minimum levels. Calcium, potassium, sodium, methionine and arginine were all below the recommended levels, nor did the Ca:P ratio meet the guidelines' recommended levels. No diet contained arachidonic acid: arachidonic acid deficiency can cause thrombocytopenia, impairment of platelet aggregation, inability to conceive and congenital birth defects (Pawlosky and Salem, 1996).
Copper concentrations exceeded legal limits in all four diets, two diets contained excess zinc and another diet contained excess iron. Some breeds of dog, especially Bedlington Terriers, have a genetic sensitivity to copper—copper toxicity is presented with symptoms of abdominal pain, diarrhoea, hyporexia, shock and haemolysis. Supplementation with zinc can reduce copper absorption, however treatment is often unsuccessful and ultimately can be fatal (Blakley, 2020). Given that both zinc and copper levels were in excess it may be that they are countering the action of each other.
Given that Zafalon's study is the most recent study to be conducted, the likelihood of advanced testing techniques can increase the reliability of the results. The main limitation of this study was the small sample size as a result of limited numbers of vegan diets available. More significantly, patient assessment and blood concentrations of nutrient bioavailability were not assessed. Although the author recommends patients are not fed these diets because of the nutritional deficiencies it cannot be confirmed that any arising illness is directly attributed to diet.
In a 2015 study by Kanakubo and a 2001 study by Kienzle and Englehard both vegetarian and vegan pet food diets were analysed. In Kanakubo's study 25% of diets did not meet the minimum micronutrient requirements set out by the AAFCO. In the two combined studies, 118 diets were analysed finding common deficiencies in protein, calcium, phosphorus, unbalanced Ca:P ratio, sodium, vitamin A, vitamin B12, taurine and arachidonic acid. Formulating a nutritionally balanced vegan diet may not be possible as some nutrients can only be derived from animal origin, such as arachidonic acid and taurine. It is well documented that cats are unable to synthesise taurine efficiently to conjugate bile acids (Pion et al, 1987), and therefore require the addition of it in pet food. Taurine deficiency can lead to feline central retinal degeneration, dilated cardiomyopathy and reproductive failure, and it is classed as an essential nutrient (FEDIAF, 2020). Plant-based alternatives to taurine and arachidonic acid are available, however, these often differ in composition to naturally derived taurine and arachidonic acid, and are required in different amounts to meet nutritional demand and bioavailability (Brown, 2009). Limitations of both studies include single point in time analysis; because of batch discrepancies the results may not be representative of other batches.
Despite being a relatively old paper, Semp (2014) conducted the largest study assessing nutritional content of vegan pet food diets and physically assessing 233 patients including the nutritional bioavailability in their blood. Participants had been fed an exclusively vegan diet for 6 months to 7 years with a mean of 2.83 years. Nutritionally, the diets were reported to have deficiencies in protein, fat, carbohydrate, potassium, methionine, cystenine, sodium and cobalamin. Cobalamin is primarily ingested from food derived from animal origin being particularly high in liver, kidney, red meat and dairy. Plants and plant products have virtually no cobalamin and carnivorous animals are unable to produce their own cobalamin. Hypocobalaminaemia is associated with nonregenerative anaemia, neutropenia and metabolic brain disorders (Kather, 2019).
Semp reported that there were no clinical abnormalities associated with feeding a vegan diet, however despite 233 participants, only 20 of these patients (8.58%) underwent blood analysis which throws into question the reliability and representability of the sample size on the greater population.
In recent years research has been conducted to investigate poor compliance of accurate labelling and undeclared ingredients in commercial pet food. The objective of Kanakubo's 2017 study was to determine the presence or absence of mammalian DNA in pet food diets marketed as vegan or vegetarian. Kanakubo et al used polymerase chain reaction (PCR) testing to analyse two samples from a total of 14 diets 3 to 4 months apart with different batch numbers. Seven out of the 14 diets were found to contain undeclared mammalian DNA with the results being repeatable in six of the diets. These findings confirm the persistent presence of mammalian DNA, however, it is not possible to ascertain if this is an intentional addition or as a result of unintentional batch discrepancies or cross contamination.
Furthermore, nutritional inadequacies and inaccurate labelling are not limited to commercial plant-based diets; a 2009 study conducted by Hill et al analysed 2208 commercially available pet food diets. It was found that for all nutrients there was a 5% to 30% discrepancy from what was reported on pet food labels to what the diet composition actually contained.
Animal welfare
Animal welfare refers to either the positive or the negative physiological and psychological well-being of animals. Fraser (2008) proposed three overlapping concepts of animal welfare:
- Physical state and functioning
- Psychological or mental state
- Ability to perform natural behaviours and live according to their natural state.
The term animal welfare however, can be interpreted to mean different things to different individuals depending on various factors. Figure 1 shows all the influences that may impact someone's opinion on animal welfare. Multiple influences over companion animal welfare can sometimes result in conflicting ideologies of how animals should be treated, their actual need and the interests involved can lead to ethical dilemmas such as whether to feed a vegan diet.
As veterinary professionals' emphasis is on physical state and functioning, to prevent bias Dawkins (1998) suggested scientific evaluation of animal welfare requires an understanding of behaviour, health and immunology to enable us to objectively determine an animal's physical and psychological state. Ethical judgement is then applied to determine whether the welfare state is acceptable or not.
Animal ethical theories
The place of animals in human society is central to veterinary ethics with animal welfare being a much-debated topic. Lund et al (2016) collected data from a questionnaire to identify the animal ethical profile of vegetarians, vegans and meat eaters. Lund found meat eaters predominantly associated with utilitarian theory whereas vegans had the strongest affiliations with animal rights views. Emphasis was on human interest not overruling animal rights as well as the promotion of respectful treatment of animals. Application and development of two of the main classical ethical theories — utilitarianism and deontology — provide a background for discussion that can be used to agree or disagree with anthropomorphism of pets.
Utilitarianism
Utilitarianist theory promotes acting in a way which maximises what is best overall and minimises what is worst, the wellbeing of every individual counts including the experiences of non-human animals. Early utilitarian theorist such as Bentham, Mill and Sidgwick all argued that non-human animals should be treated as equals to people. In a practical sense, it is not possible to completely eradicate animal exploitation or animal suffering therefore more current utilitarianists such as Singer and Matheny accept the use of non-human animals as long as they do not suffer (Singer, 1998). It can be morally justified to eat meat as long as it is not confined, allowed to perform natural behaviours and killed quickly without fear or pain. A Utilitarian approach can be interpreted to support or oppose veganism in companion animals; by feeding commercial vegan diets you are abstaining from the use of production animals therefore maximising their welfare, however, this may be at the detriment of companion animal health as demonstrated earlier. It can be argued that it is perfectly acceptable to feed meat-based pet food as long as the animals have been reared in the most ethically possible way.
Deontology
Deontology quite simply determines right from wrong — early theorist Immanuel Kant argued universal laws are required to govern people's behaviour. His moral laws referred specifically to humans with very little thought regarding animal wellbeing. More recently Regan claims Kant's intrinsic values can include animals; despite them being non human, they still have their own life and their own life experiences.
Regan's view is that animal exploitation should be abolished: no animal should be the property of a human. In 2004 he wrote:
‘Being kind to animals is not enough. Avoiding cruelty is not enough. Whether we exploit animals to eat, to wear, to entertain us or to learn, the truth of animal rights requires empty cages, not larger cages'.
(Regan, 2004: 10)
In terms of veganism in companion animals, although deontologists may support a vegan lifestyle, they would not support the ownership of a companion animal.
Even among ethical theorists there are disagreements, everyone interprets ethical theories in their own way based on their own experiences. Although people will never agree, ethical theories can be helpful when deciding how to act. Despite having differing perspectives on a lot of issues, a common theme among most ethical theories is that animals should be treated with respect.
Legal implications
The Animal Welfare Act (2006) is the principle animal welfare legislation, secondary legislation such as the codes of practice can also be used to promote animal welfare. A person commits an offence if they do not adequately ensure the needs of an animal they are responsible for are met. The needs of the animal include:
- A need for a suitable environment
- A need for a suitable diet
- To be able to exhibit normal behaviour patterns
- To be housed with or apart from other animals
- A need to be protected from pain, suffering, injury and disease. (Animal Welfare Act, 2006)
It could be argued that if any diet-induced disorders are present as a result of nutritional inadequacies from feeding commercial vegan diets, an owner may be liable to prosecution for failing to treat or prevent them. In reality, it is unlikely an owner would be prosecuted and are more likely to receive advice or assistance from a regulatory body such as the RSPCA.
Case reviews
Case one — an 11-year-old female neutered Greyhound
Presentation: The patient initially presented in 2018 to receive radiotherapy for multiple soft tissue sarcomas. The patient was on long-term meloxicam and 250 mg paracetamol three times daily (TID) due to osteoarthritis. On clinical examination the patient was bright, alert and responsive with an ideal body condition score (BCS) of 4/9. Her clinical examination was unremarkable. Routine haematology and biochemistry were analysed. Haematology revealed a neutropenia, a very mild anaemia and a mild lymphopenia. Biochemisty revealed a low cholesterol and low lipase.
The patient's mild anaemia could be associated with decreased dietary cobalamin, deficiency of phosphorus which leads to a destruction of red blood cells or deficiencies in iron, copper riboflavin, niacin and vitamin (Marks, 2017). The majority of these micronutrients were reportedly below minimum levels in some of the vegan diets analysed. Chronic inflammation and tumours can also cause anaemia both of which the patient had been diagnosed with.
Case two — a 14-year-old neutered male cross breed
Presentation: The patient is under long-term care receiving chemotherapy to treat multiple soft tissue sarcomas, Horner's syndrome, a tumour of the parathyroid gland, which underwent surgical excision, and he has osteoarthritis on the hind limbs and lumbar spine for which he is receiving robenacoxib 80 mg once daily and paracetamol 500 mg TID. On representation the patient was bright, alert and responsive, he was severely obese with a BCS of 8/9. Routine haematology and biochemistry were performed revealing a decreased mean cell volume, lymphopenia, increased urea, lipase, albumin and alkaline phosphatase.
A decreased mean cell volume can be attributed to anaemia and an iron deficiency. None of the studies conducted reported any deficiencies in iron, however, the recommended dietary iron intake is 80 mg/kg, and deficiencies are seen in vegan or vegetarian diets without adequate supplementation although this is rare (Michel, 2006). Foods high in iron are muscle meat, liver, egg yolks and some dried beans.
Case three — an 11-year-old neutered male Labrador
Presentation: The patient has a pulmonary mass, osteoarthritis, intravertebral disk extrusion and a history of chronic diarrhoea. The patient re-presented because of sudden onset of pyrexia and lethargy. On presentation the patient was quiet, alert and responsive, he was pyrexic with a rectal temperature of 40.7oC, BCS was 7/9. He was tachypnoeic and tachycardic with a mean arterial blood pressure of 60 mmHg.
Routine haematology and biochemistry were run which revealed a raised alanine aminotransferase, alkaline phosphatase, gamma glutamyl transferase and low magnesium. Hypomagnesaemia is frequently found in critically ill animals and is often associated with a guarded prognosis. There are various causes one of which is dietary insufficiency — if found to be related to diet, treatment is often simple and requires supplementation or changing to a diet with increased calcium levels (Dhupa, 1998).
Discussion
No owner interview was conducted as part of the case studies, and this would have been beneficial to gain greater insight into why they chose to feed their pet a vegan diet and how long they had been feeding a vegan diet for, and what effects they believe it had on their pets.
The patients in both case one and case two were under long-term care for staging and treatment of cancerous tumours. Companion animal oncology is one the most rapidly progressing fields of veterinary medicine and provokes a lot of debate among veterinary professionals and clients. It takes a very dedicated owner to embark on a chemotherapy and/or radiotherapy schedule; they are often ruled by an intense treatment schedule, require a lot of medication and are not given without their own risks of side effects. It is understandable then that these owners would research alternative therapies to use concurrently with cancer treatment.
The owners of the patient in case one were reportedly feeding V-Dog after researching their claims that it is a natural anti-inflammatory which reduces joint pain and improves mobility, as well as having the ability to ‘supress cancer growth and kill cancer cells’ (V-Dog, 2021). V-Dog's claims are reportedly taken from research conducted in human medicine, however these claims are yet to be researched in companion animals therefore no assumptions can be made as to its anti-inflammatory or cancer fighting properties.
The owner of the patient in case two was following the ‘Joanna Budwig’ diet which claims to treat arthritis, cancer, cardiovascular disease, diabetes and liver disease (Skelton, 2016). The diet is primarily a vegetarian diet designed for humans, and is based on feeding high levels of flaxseed, cottage cheese, milk, fruit and vegetables. It has been adapted to feed companion animals permitting some high quality, organic meat and fish to be added into the diet.
Research in human medicine has found that omega 3 fatty acids and flax seeds reduce some chemicals associated with cancer (Freitas and Campos, 2019). Cancer research UK have released a statement stating that a lot of these claims are still undergoing extensive research and specifically that the Budwig diet is lacking in many nutrients and that despite Budwig's claims, there have been no clinical trials to support them (Cancer Research UK, 2018).
The patient in case three was primarily fed a vegetarian commercial dog food diet (unknown brand) with the owner adding fresh vegetables and rice. The owner reported that the patient was ‘allergic’ to most meat-based diets which resulted in chronic diarrhoea, therefore had eliminated them from his diet, although this has never been investigated. Dietary intolerances are characterised by generalised pruritus, digestive upset and chronic skin conditions (Hills Pet Nutrition, 2020). Dietary elimination trials are frequently performed with dietary intolerances however rather than eradicating protein from the diet it is advised that it is swapped for a diet with a novel protein or a commercial diet specifically designed to reduce the symptoms associated, allowing for complete nutrition.
As part of this review, The Vegan Society were approached to ask for scientific peer-reviewed evidence to support feeding companion animals on a meat-free diet. In their response, they were unable to direct the author to any literature apart from blog posts and testimonials on their website. The Vegan Society did, however, state that they recommend owners do what is best for their pets and seek advice from a veterinary professional before changing onto a vegan diet. The British Veterinary Association (BVA) and the Royal Society for the Prevention of Cruelty to Animals (RSPCA) both state they do not recommend vegan diets to dogs or cats. In a statement for the BBC Daniella Dos Santos, Senior Vice President of the BVA stated that ‘vegan diets are not designed to meet the welfare standards of your pet, for that reason we would not advise a vegetarian diet, let alone a vegan one’ (Dowling, 2020).
The positive impact of adequate nutrition is well established in veterinary medicine, and incorporation of regular nutritional assessments allows for maintenance of patient health and their response to disease. Client communication and compliance are essential for maintaining targets and expectations. Veterinary nurses play a major role and many practices offer free nutrition clinics which should be utilised. The World Small Animal Veterinary Association (WSAVA) have formulated a two-part nutritional assessment shown in Figure 2, which veterinary surgeons and veterinary nurses are able to conduct as part of regular patient monitoring.
Full medical history, BCS and muscle condition score formulate the basic nutritional screen, any abnormalities identified should prompt further investigation into the patient and their diet, and formulation of a treatment plan.
The 2014 study conducted by Semp is the most comprehensive study for assessing the effects of vegan diets on companion animals as it assessed nutritional content of the diets, and conducted health assessments of patients fed the diets, despite being in a very limited manor. It can be adapted to provide more representative results by ideally conducting multiple nutritional dietary analyses over different time frames and to include different batches. Running concurrently to the dietary analysis, the patient should be screened at regular intervals following the WSAVA assessment guidelines (Freeman, 2011). Routine haematology and biochemistry should also be conducted to assess for nutrient bioavailability. Any alterations in diet or dietary supplementation should be recorded and followed up with assessment to determine progression or improvement.
All three case studies presented to a referral hospital for investigation of medical conditions for which they were already symptomatic, often with multiple comorbidities. The cause of abnormalities on haematology could not be definitively determined, and could result from their disorders, the treatment they were receiving, or their diet. It is, therefore, not possible to determine the full effect of the diet on these patients. Conducting a study using only healthy, asymptomatic participants fed vegan diets would allow for more association with blood abnormalities and diet.
Conclusion
Companion animals fed improper diets may develop health and welfare problems, and inappropriate diets can result in nutritional imbalance or malnutrition. Feeding vegan diets to companion animals should be approached with caution; much of the research conducted has found that despite correct labelling, commercial vegan diets do not meet the legal nutritional guidelines putting pets at risk of diet-induced disorders.
The reason for feeding an inappropriate diet may be related to the owner's lifestyle, their own diet, anthropomorphising animals and their own personal or religious beliefs. Vegan owners in particular are morally and ethically conflicted with their decision-making because of their own personal beliefs. Additionally, societal norms, socioeconomics, inaccurate or unscientific information from various sources can mislead or misinform well-meaning pet owners. Owners should be aware that any nutritional inadequacies and dietinduced disorders are likely to negatively impact a patient's welfare and could in theory make owners liable to prosecution if they are unwilling to follow expert veterinary advice.
Further research is required to understand the long-term effects of vegan diets on carnivorous patients, until then veterinarians must utilise the information that is available ensuring a proactive approach to prevent, treat and educate owners regarding any diet-induced disorders to ensure the best patient welfare.
KEY POINTS
- Veganism is on the rise both in humans and in companion animals with many owners citing animal welfare as being their primary reason for adopting a vegan lifestyle.
- Feeding companion animals vegan diets is subject to legal, ethical and welfare implications. Feeding a vegan diet to dogs and cats significantly impacts their welfare as it puts them at undue risk of developing diet-induced disorders leaving owners liable to prosecution if they are unwilling to adhere to expert recommendations.
- As commercial vegan diets are a relatively new phenomena, more research needs to be conducted to understand the nutritional impact including the longand short-term effects. In the meantime, veterinary professionals should continue to educate owners on suitable diets based on the individual's requirements.