I would have to agree with Jon and Rhodie...getting first hand experience is the only way to go. Once you already know the basics, books can be invaluable in braodening your knowledge base, but you just cant do it from scratch.
Do you have any experience with large animals at all? Having animal sense is also something you cant learn from a book and I would strongly suggest working on someone elses farm for a bit just to see if you a) enjoy it and b) have a feel for working with livestock! You may for example find that you prefer working with sheep than cattle!
Good luck and keep us informed!
PS what country are you in just out of interest?