What degree do I need to be a large animal veterinarian
What is the best school and subjects to take

In the USA, it requires a four year degree and licensure. Here's a good page (http://education-portal.com/articles/Veterinarian_(Livestock):_Educational_Requirements .html) discussing the educational requirements for a livestock vet, with info about schools in the USA. If you live in a country other than the USA, you probably want to Google "livestock veterinary schools countryname".