I would criticise those who are accusing OP of not being 'ready' for veterinary science due to their views about animals. There is a massive difference between the unnecessary slaughter of animals for food production, and euthanasia for the animal's benefit. If the euthanasia contravenes ethical guidelines then you can refuse, because we have to have the welfare of the animal at best interests. I'm sure OP knows that the veterinary profession is not about 'cuddling puppies', and that is incredibly patronising to say just because they do not believe animals should be exploited for food.
Anyway... I am the same as OP. I am opposed to the meat and animal food industries, and I am a future veterinarian as well. I too am dreading the abattoir visit (which is essential) however you have to have to right mindset about it.
For instance, if you are educating meat-eaters about where their food comes from and how cruel the process can be, your argument bears more weight if you can say "I've been to an abattoir and seen it happen" than "I watched a video online/read information about it". Therefore, you can use this experience to help craft your arguments/debates. Use it to teach people and hopefully deter more people from contributing to the awful animal food industries!
I agree that the experience will be horrible, I am going to have to do it as well, unfortunately, and will hate it... but the best thing to do seems to be to choose a SMALL abattoir. The large-scale industrial ones will kill the animals using machines and be more cruel than small abattoirs where fewer animals are killed per day, and it is done by hand. A vet I spoke to did her abattoir placement at a tiny slaughterhouse where only 1 animal was slaughtered each day, so it doesn't have to be terrible.
@polkadotti I wish you luck. As a fellow vegan vet, I understand how difficult the journey will be, especially as many of the other posters in the thread are already doubting you. Some of the animals you dissect will be euthanised shelter animals, which I initially struggled to come to terms with it, but if you think about it... these animals will be killed anyway, there is NOTHING we can do. So we might as well make their lives mean something by educating us future vets, which in turn will help us learn how to treat and save more animals in the future!
So OP... unfortunately the abattoir is mandatory, however you are not alone in your beliefs. Myself and other vegetarian/vegan vets-to-be are here. I understand your fears, I am also scared that the slaughterhouse experience will haunt me forever, but I think in the long-term, that is only a small portion of your life (some unis only demand you spend 1 day there, which isn't a lot at all) if you think about the benefits for the future. You can spend the rest of your life following your passion and helping animals.
Sorry, this got kinda long.