The way vet school generally works is that you first get a Bachelors degree and then during your senior year you apply to the Veterinary schools you want to go to. So by going to A+M now no way ensures that you get into the vet school there.
So before vet school you are going to need 4 years of college. That is something you can do anywhere(not necessary A+M). You could go straight into a 4 year school or you could do 2 years at a community college and then finish up at a 4 year university. Which you choose to do is up to you and will depend on your situation.
Either way you are going to be looking to complete all the necessary pre-requisites for the Veterinary schools you plan to apply to. You can do that as part of any major, so pick one that appeals to you. You are also going to want to make sure you get very good grades as they are important when it comes time for you to apply.