From what I have seen they mainly use animals that have died naturally or have been euthanased, but only if they have the owners permission. They possibly use specifically killed animals for some things but I don't really know a lot about it to be honest, best person to ask would be a vet or vet student. I didn't see or hear of any kind of vivisection at the vet schools I have visited, I think that any procedures done by students on live animals are only done if the animal needs it and they are closely supervised by the vets. I do know that animal research does take place in other parts of the Universities though.