Like many vets, I chose my profession when I was ridiculously young: around five years of age. My decision was based on affection and empathy with the animals in my life: a predilection known as “love of animals”. I've always had an innate sense that animals are the same as ourselves in many ways and that they deserve our care and affection.

So how can it be, then, that I, like most veterinarians, am a meat eater? How can we justify killing and eating living creatures that we care about?

From an early age, most vets have been surrounded by a culture which teaches three key facts which we have absorbed and accepted.

Farm animals aren't aware they will soon become food Credit: Alamy

First, farm animals have a smaller forebrain than ourselves, so they are not able to reflect upon the fact that in some days, weeks or months, their lives will be ended to provide their keepers with a food supply.

Second, animals live in the present moment far more than humans. So as long as they are contented and comfortable for most of their lives, it does not matter if they die at an earlier time than a natural death. And farm animals do not seem to mourn the death of others in their group in the same way as we do.

Third, it is acceptable for humans to take the lives of farm animals, as long as this slaughter takes place in a manner which is humane: the animal must not know that it is about to happen, there is a stunning process which causes instantaneous unconsciousness, and there is no pain or distress before or during slaughter.

These three facts have been backed up by a belief that the legislation and systems in the UK and EU are sufficiently rigorous, well designed and implemented so that farm animals have a life worth living and a death free from fear and pain.

Many of us attempt to justify why we eat meat Credit: Alamy

It's this background that allows vets to justify meat eating: indeed, it's only with the professional help of farm vets that livestock can be kept at all, and only with the help of vets staffing abattoirs that animals can be legally killed.

These vets carry out the difficult and pressurised job of trying to maintain welfare regulations, sometimes under intense scrutiny and commercial pressure.

Yet in recent years, I, along with many other vets, have found myself questioning my beliefs for a number of reasons. I've read books about factory farming that describe how intelligent animals like pigs suffer unbearably on their way to our plates. Undercover activists (now called “terrorists” in the US) have used hidden video cameras to expose vicious cruelty in intensively reared farm animals. Meat from animals that are slaughtered without pre-stunning routinely makes its way onto supermarket shelves. A recent bestselling book described factory farming as “the greatest crime in human history”.

While I try to reassure myself that in the EU (unlike the US, China and most of rest of the world), animal welfare legislation protects animals, cognitive dissonance is creeping in. Do I really believe that intensively kept pigs ever have the opportunity to exhibit the natural behaviour that makes life worth living? Is it ever possible for cows to have a tolerable existence if they never graze on a field of grass?

A Hong Kong Vegetarian Society activists lies on a giant plate alongside oversized peas, carrots and cutlery during a protest rally Credit: Jerome Favre

Fuelling this dissonance, in the thirty years since I qualified as a vet, our understanding of animal sentience has increased exponentially. With the assistance of dynamic imaging techniques, we now realise that animal brains are far more like our own than we'd like to think. Fundamental aspects of consciousness – emotions, pain and pleasure – emanate from the primitive parts of the brain that we share with other species. The main anatomical difference – our large forebrains – allows us to ponder the past, present and future, and gives us a rational ability to organise ourselves more effectively than other species, but that's about it. There is no clear line delineating humans from animals. Pete Singer was right in his seminal book “Animal Liberation”: we choose to mistreat and then to eat pigs, but it's hard to find a rational reason to justify this, other than our own invented excuse that they are a different species.

Finally, recent media coverage has made the point that the contribution of livestock farming to man-made greenhouse gas production is immense, accounting for 14.5% of the total, around the same proportion as direct emissions from cars, planes, trains and ships combined. Land clearing for cattle production is destroying rain forest acreage.

Meanwhile, intensive meat and milk production is an inefficient method of transforming vegetable protein into animal protein in a world where people still go hungry. All in all, it seems that livestock production is far from environmentally ideal.

Up until now, I have justified my own meat eating by telling myself that I only consume ethical products, such as free range chicken and locally reared cattle and sheep. Yet if I'm honest, I know that my buying choices are easily blurred: sometimes the provenance of the meat I buy may be uncertain. And when I am away from home, eating in restaurants and at friends, I often have no idea where my food comes from. So it's likely that my own eating habits support intensive factory farming, and I don't like that.

There is an appealing answer: if a clearer line was defined, it'd be much easier to stay on one side of it. Vegetarians don't eat meat anywhere, at home or away from home, so there's no risk of accidental supporting of factory farming.

I still believe that it can be justifiable, under ideal circumstances, to drink milk, and to eat meat and eggs. But in this world of global markets and vague labelling, it's increasingly difficult to be sure about what you are consuming.

Vegetarianism, and indeed veganism, has never seemed more appealing.

For a trial period of one month, Pete is taking part in Veganuary, to experience for himself the life and diet of a vegan. If you'd like to take part, see this website for more details.

To comment, visit Pete's Facebook page: Pete the Vet