Food animal, equine, exotics, zoo, wildlife, etc. You don't NEED every category, but most schools like to see some variety in experience. Veterinary experience is most important, but animal experiences not supervised by a veterinarian (e.g. cleaning cages in a shelter) is also good to have. Research experience is always good too, especially if you're considering going into research. Leadership experience is another good thing to have, as well as extracurriculars in general -- actually being involved, not just going to a few meetings of some random club. Vet schools like to see that you have a life outside of classes and getting veterinary experience!
Even if you only plan to practice small animal medicine, you will most likely be required to have some prior experience with farm animals as well. To gain some, I would suggest working/volunteering at a stable or farm.
Like LetItSnow said, it's not required to have experience with farm animals at all. I didn't have any and I was still accepted into several schools - some schools do require having at least several hundred hours of veterinary experience. Having large animal experience will be beneficial to your portrayal as a well-rounded applicant, yes, but veterinary schools will be looking for diversity in veterinary experiences.
No school explicitly requires experience with large animals. Several schools do require experience with veterinarians in general.
It may be an unwritten requirement at some schools (i.e. you won't see people getting in without some large animal experience) but I don't know of any school that actually has it as an explicit requirement. Most of the time schools don't really say specifically what type of vet experience they want you to have at all.
