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Cat Veganism: can it work or does it defy biology?

How many owners are feeding their pets a vegan diet is unknown. However, while clearly not yet mainstream, discussion on social media about meatless diets for cats and dogs has been on the rise in the last five years and commercial vegan pet foods are entering the market.

We asked Shiva Greenhalgh from Sydney Animal Nutrition to weigh in on this debate and to separate facts from fiction based on the latest scientific research ...


Introduction

Decision-making on what food to consume can not only be based on nutrition and taste, but also reflect the ethical framework in which someone lives. 

Veganism is the most pertinent example and people rejecting the consumption of animal products is on the rise. While veganism has existed for thousands of years due to religious restrictions on meat consumption, its recent Western variant is interested in the reduced impact on the environment, purported health benefits and approach to addressing animal welfare concerns

If it offers a moral and healthy alternative for humans, some are beginning to ask why veganism could not be extended to pets?

Interest has also been brewing for some time with studies on vegetarian diets for pets dating back 20 years. Now is a good time to reflect on the nutrition needs of companion animals and consider whether this trend is good or could be doing harm to our pets. Due to differences in the nutritional needs of types of animals, this article will focus on our feline friends.

The Cat: Evolution, Biology and Metabolism

Domestication of the cat occurred approximately 10,000 years ago as a companion animal and to hunt pest species on our behalf. Unlike dogs (domesticated 16,000 years ago), cats were less reliant on our food scraps which meant that they did not undergo the same level of biochemical, behavioural and genetic change. 

Changes in dogs meant that they could thrive on an omnivorous diet, while cats maintained their ancestral diet as an ‘obligate carnivore’ (reliant solely on animal tissue) sourcing energy from meats, fish and other animal products.

The difference between the two is stark. Cats have protein requirements which are two-three times more than an adult omnivorous species
Ancestral and wild cats survive on prey which they sense and capture, their canine teeth masticate (chew) rather than grind (as herbivores do) and possess short intestinal tracts with differing enzymes and gut flora suited to digesting animal-based protein. 

Unlike omnivores who derive most of their energy from carbohydrates, obligate carnivores use protein for maintenance of blood glucose concentrations even when sources of protein in the diet are limited. 

Cats can use carbohydrates as a source of metabolic energy but are limited in their ability to spare protein utilization by substitution of carbohydrates. In other words, we are talking about an animal which is suited to meat-based diets and it is a tall order for veganism to offer an alternative which meets the needs of a creature specifically suited for meat eating.

What are the concerns of a vegan diet for cats?

When visualising cat food, images of fish, cans of tuna and raw chicken can come to mind. Although we can visualise how to make it, most consumers opt for commercial pet food
This allows the complex dietary requirements of cats to be overlooked as products take the guesswork and labour out of feeding. We put faith when they claim that they have been scientifically formulated to meet the needs of our pets.

The existence of commercial vegan pet food has been taken as evidence that it must meet nutritional requirements. This is not necessarily correct, with one study (Gray et al, 2004) finding that a commercial vegan food advertised as balanced was found to be taurine and arginine deficient

Even conventional pet foods have sometimes struggled to meet the nutritional levels recommended by the NRC (the peak scientific advisory body in the United States responsible for animal nutritional standards) (Raubenheimer et al, 2016).

Plant-based diets are often not appetising

Vegan diets (unlike vegetarian diets) are completely void of any animal-derived products which can act as an alternative source of protein (e.g. eggs, milk and cheese). 

The absence of meat and these other products means palatability is likely to be an issue. Cats can be highly selective in what they eat even in the absence of alternatives. Even if they do eventually eat the food, eating less of it will lead to weight loss with long-term health consequences. Prolonged periods without or with insufficient food places the animal at high susceptibility of fatty liver syndrome if already underweight.

Flavour enhancers (e.g. nutritional yeast and vegan mock meats) could encourage cats to consume vegan diets although they may still refuse if unwell. New vegan commercial brands have implicitly acknowledged this problem by marketing their use of flavor enhancers, supplementation and enzyme powders to entice cats. 

The use of these synthetics is not promising, and a recent study found that, while flavour and aroma may influence diet selection in the short term, macronutrient balancing (i.e. the right mix of proteins, fats and carbohydrates) is the primary driver of what an animal will seek to eat long-term.

Plant and animal proteins are NOT equal!

Protein is the most crucial macronutrient for cats. Protein is a source of essential amino acids and nitrogen used for synthesising nonessential amino acids. These are essential for energy and renewal of nitrogenous components of the body. This is how the body can sustain and build your muscles, skin, blood, hair, nails and DNA.

In cats, there are 11 essential amino acids. The most well-known, taurine, shows the importance of meat to cat diets. High concentrations of taurine are in heart tissue and seafood and to a lesser extent in meats and dairy products. 
Even in meat diets up to 80% can be lost in the process of cooking and studies have found that taurine deficient diets can lead to cats suffering degeneration of the retina (leading to blindness) and cardiomyopathy (affecting how the heart muscle pumps). The use of lactaalbumin in milk or egg albumin can potentially reverse and prevent these issue, but these options are not available in vegan diets.

Non-essential amino acids (which use nitrogen from protein) may also become essential where an animal has an underlying disorder that interferes with synthesis of the amino acid or results in its excessive consumption or loss.

Vegan diet proponents are quick to point out that plant matter includes protein. However, there are key differences between the two in their amino acid profile (rate of absorption and utilisation in the body).

A key difference is the ‘biologic value’ of the protein. This is the number and types of essential amino acids it contains, its digestibility and how it is metabolised. A higher value means less protein is needed to meet essential amino acid requirements. 

Vegan diets do not include proteins with high biologic values including egg, organ and skeletal meats. This is a problem because cats have high protein requirements (a minimum of 3.97g of protein of high biologic value per kg metabolic body wt/day). 

Consuming plant-based protein sources mean that the protein requirement is higher. Too little high biologic protein in the diet can cause an apparent protein deficiency. This can cause significant harm including reduced growth rates in kittens, weight loss, reproductive issues, weakened protection via vaccination and failure to respond effectively to treatment of disease and injury.

Vitamin A deficiency

Vitamin A is also missing naturally from vegan diets. Unlike dogs, cats cannot convert beta-carotene found in vegetables to vitamin A. Their source can only be derived from animal or animal products such as liver, cod-liver oil, eggs or cheese

You can offer your cat scrambled, hard-boiled or poached eggs as a treat, but NEVER serve raw eggs!

Cats also need a preformed source of arachidonic acid which is also found in cod liver oil and a plentiful supply of taurine. Without accounting for these needs, cat’s muscles will deteriorate.

Supplementation as the solution?

Supplementation can help balance out diets and is common in commercial pet foods. However, the sheer amount of issues associated with plant-based foods for cats mean that a significant amount is required in precise proportions

It can and is often overdone to the detriment of the animal. Over-supplementation of vitamin, minerals and amino acids can impact development and interactions in metabolism which nullify their benefits. Excessive calcium, phosphorous and vitamin D is especially dangerous leading bones to calcify unevenly, calcium deposits in the heart, lungs and blood vessels causing tissue to lose elasticity. 

High concentrations of vitamin A can also cause bone spurs to develop in and around the joints. The absorption of nutrients is best derived from food rather than supplementation where possible.

Veganism increases risk of FLUTD

Alternate diets that are not correctly formulated and fed can result in acute or chronic illness. However, even if properly formulated, cats on vegan diets remain at a particular risk of developing Feline lower urinary tract disease (FLUTD) which is the most common disorder affecting the lower urinary tract in cats. FLUTD also has a high chance of recurrence if dietary factors remain unchanged.

Vegan diets affect the concentration of urine in cats. Cats on vegan diets can develop high pH (alkaline) urine due to the higher pH of plant-based proteins in their food. When it is too alkaline, there is a risk of bladder crystals or stones. While urinary acidifiers could help mitigate this issue (where required), it would be yet another thing for pet owners to monitor as part of formulation.

Concluding thoughts

An interest in increasing the uptake of veganism in humans to address societal, animal welfare and environmental problems can be commendable. However, the unique and complex nutritional requirements of carnivorous cats mean that their adoption of this diet is difficult and risks negative health outcomes. 

Once the harm associated with nutritional deficiencies sets in, maintaining the diet could lead to rapid decline. However, studies on vegan diets remain limited which means that anecdotes of success stories remain powerful for new converts to pet veganism.
Commercial vegan pet food may continue to improve and find solutions to the issues discussed, but should not be taken at their word when making claims of currently being nutritionally complete, balanced and palatable. However, taking feed formulation into your own hands is difficult.

Owners who remain interested in putting their cat on a vegan diet are recommended to do so with the guidance of a veterinarian nutritionist or animal nutritionist to ensure factors of nutritional requirements and palatability are met.

While vegan diets may be very difficult for cats, a vegetarian diet offers a greater variety of ingredients which could meet the protein and fat requirements of the animal. As it is arguably in the biological make-up of the cat to consume meat, this diet still requires significant work to ensure it is meeting their nutritional needs and expert advice should be sought.

* Details of minimum requirement levels for cats can be found at
https://www.msdvetmanual.com/management-and-nutrition/nutrition-small-animals/nutritional-requirements-and-related-diseases-of-small-animals 

written by Shiva Greenhalgh, April 2019 for Australian Dog Lover (all rights reserved).

About the writer

Shiva Greenhalgh is an animal nutritionist and owner of Sydney Animal Nutrition, which specialises in companion animal nutrition advice.

Shiva holds a Bachelor of Science (Zoology) from Western Sydney University and a Masters in Animal Science (Animal Nutrition) from the University of Sydney.
Shiva is also member of the Nutrition Society of Australia.
In her spare time Shiva volunteers for WIRES, educating the public on native wildlife.

Sydney Animal Nutrition services all of NSW, and can accommodate interstate pet owners. To have a chat about your pets' nutrition or to find out more, please visit www.sydneyanimalnutrition.com.au

or the Facebook page 

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