Although cats naturally consume a small amount of vegetable matter – in the gut of prey for instance, the occasional consumption of grass or a bite of fruit/vegetable apparently for the novel flavour – their own digestive system cannot break it down. The vegetable matter from their prey's gut is already partially digested. Vegetable matter they consume for themselves, acts either as roughage or an emetic. Only where their teeth have broken down cell walls are they able to digest it. Unlike herbivores, cats' teeth are not designed for chewing vegetation to aid digestion and they derive little nutrition from grass, fruit or veg (indeed, vets recommend adding cooked vegetables to an overweight cat's diet to provide indigestible bulk, much as humans eat bran cereal).

Although some cats enjoy a vegetable treat, their short gut lacks the enzymes and structure for digesting grains, fruit or vegetables. They lack the grinding teeth and digesting vat stomachs of herbivores. Their livers are poor at removing the toxins found in many plants as they rely on their prey to have already eliminated plant toxins (this poor liver function also makes them susceptible to poisoning - many human-safe drugs and essential oils are toxic to cats).

Grain-based cat foods (which contain meat byproducts) must be specially processed to break down the cell walls to make the foods digestible for cats. Even so, some cats have digestive problems when fed on these foods (known as "dry food", "crunchies" or "kibble") and suffer diarrhoea and vomiting, even on "premium" quality dry food. In my experience (and that of some British breeders/owners), Persians seem more prone to this, which has led to some special formulations for Persian cats.

Commercial pet foods may not be perfect, but they do contain meat and/or fish derivatives and they do not attempt to prevent a cat eating meat. The cereal content is aimed at producing a lightweight, long shelf-life biscuit texture while keeping cost down rather than imposing vegetarian beliefs. In the past, some misguided individuals have tried to feed cats a vegetarian diet. The result is malnutrition, particularly taurine deficiency. Growth is stunted and the fur become unkempt (a huge amount of energy goes into fur growth). On such diets, cats eventually go blind. One such case was presented at a Feline Advisory Bureau conference in the mid/late 1990s and vets still see the results of misguided or fanatic owners trying to impose their "meat is murder" beliefs on cats.

Sadly, some misguided individuals still insist on feeding vegetarian or vegan diets to their cats. Although the diets are now formulated to contain necessary nutrients, it remains an unnatural diet for a cat. While laboratory analysis may consider that a supplemented vegetarian diet meets the cat's nutritional needs, lab analysis is different from how a cat's digestive system and metabolism work to extract nutrients from a foodstuff. A vegetarian-based diet may cause problems for the feline gut because its enzymes are specific to a carnivorous diet. It is cruel and unethical for a human, adapted to an omnivorous diet, to impose their dietary beliefs on a pet.

A cat is a predator and an obligate carnivore.

The meat for cat food primarily comes from byproducts of the animals reared for human consumption and carcases passed fit for human consumption. In some countries, it may also come from large roadkill, dead police-horses and similar "waste". Since the food animals are being reared for humans, not specifically for pet food, there is no inconsistency in feeding meat to pet cats even if the owner does not eat meat him/herself. As long as there are meat-eating humans, there will be byproducts that go either into pet food or are rendered into fertiliser. Cat food made from these byproducts does not increase the demand for animals farmed for meat.

If your religion means one type of animal is forbidden (either sacred or unclean) that is not an issue. There are plenty of other meats apart from beef or pork. Some of my friends put a non-religious family member in charge of feeding the cat and feed it in an annex to prevent the forbidden meat entering the family home. Others simply choose alternative flavours that don't contain that one type of meat. The cat is not being denied its basic physiological right to a carnivorous diet.

However, if you cannot tolerate a cat's carnivorous diet it is the wrong pet for you. Get a rabbit instead – rabbits can be housetrained, are affectionate is socialised from a young age and have a vegetarian diet. Plenty of people have house-rabbits. It is wrong to enforce your own dietary beliefs on an animal. A cat does not have human morals and, more importantly, it evolved to fill a specialised predatory niche. If you cannot accept this, it is the wrong pet for you.

It is wrong to impose your own moral codes on cats or judge it by your own morals. It does not have human morals regarding killing and eating other animals. It has no concept of murder - for a cat, meat is survival. If you cannot cope with this you are not suited to owning a predator that is physiologically reliant on meat. What you would be doing would be the same as happened in the Middle Ages when domestic animals were tried and sentenced in courts of law, being judged using Christian beliefs, and were even executed for their "crimes".

A vegan who truly believes in animals rights must also aknowledge and uphold the rights of cats to eat the diet they have evolved to eat and to which their physiology is adapted. A vegan who cannot tolerate feeding meat to an obligate carnivore pet should have a herbivorous pet rather than abuse the rights of a carnivorous one. Attempting to feed it a supplemented vegetarian or vegan diet is both misguided and an abuse of its rights to a species-appropriate diet.

In some legislatures, failure to provide a suitable diet for a pet's needs and lifestyle is an offence. Imposing your own beliefs and a vegetarian/vegan diets on a carnivore is not only an unenlightened Middle Ages attitude, it may result in criminal charges as you are failing to provide a suitable diet. "Suitable diet" does not just mean having the right balance of nutrients, it means the type of diet the cat evolved to eat i.e. meat-based.

Sadly, some organisations pander to this misguided mindset by offering vegetarian or vegan cat diets. If these societies are opposed to pet being fed an appropriate meat-based diet they should be advising members to get a different sort of pet. Promoting vegetarian diets for obligate carnivores is irresponsible. These societies may claim to support ethical treatment of animals by removing meat from the diet (due to farming practices etc), but in doing so they are promoting cruel and unethical treatment of companion animals by imposing an unnatural diet.

By all means refrain from eating meat yourself. You have a right to decide what you put on your own plate. Pet cats have a right to eat an appropriate meat-based diet. If you are not prepared to provide such a diet because of your own vegetarian/vegan ideals then you are not suited to owning cats as pets. Instead of feeding an unnatural diet to an obligate carnivore, get a pet that better suits your beliefs.