Hi, the entry requirements for veterinary are chemistry and biology and another a level subject of your choice, so it's pretty much like medicine.
In order for you to do chemistry and biology at a level, the you need two 6s in two sciences at GCSE and most colleges don't accept combined/trilogy science, they prefer triple science and I think it's fair because I do biology A level and I did triple science at GCSE and got a really good grade but still finding a level biology hard (the same goes to chemistry a level).
My advice would be try to do triple science if you are still in year 10 or if it's possible to do so at your school or at least just do the higher trilogy and speak to the colleges you will be applying to, to make sure that you are able to do chemistry and biology.