Hi Louis, Being a livestock vet is hard work but very rewarding and well paid. Go to your local farm vet practice and ask for a weekend job or ask if you can go with them in the holidays.
I agree, try to get some work experience and be prepared to get covered in the most unpleasant substances! Also remember that being a vet requires a strong stomach and a sensible head, you will see the worst of animals too.....
There is also the problem that large animal practices are becoming few and far between. Our local practice dropped the farm work this year and I had to change after being with them 17 years. The new practice is further away and covers a very large area. Basically it seems that new vets are not prepared to do the antisocial hours away from the surgery. I wanted to do large animal work when I qualified in 1975 but all I could find was Laboratory work with MAFF (as DEFRA was then). However, it paid well at the time.......! Good luck anyway.
I don't want to rain on your parade but you will need top marks at school to get into a vet course at university they are very competitive and there are not as many jobs as there used to be especially in large animal practice. Having said that if you really want it then go for it!