Sometimes the smells can be a little...errm, strong! Keep at it though!! I think I'm lucky in that I'm not really phased by anything (the one thing that has ever got to me on work exp is when an old lady came in with her old golden retriever that she'd rescued years ago...and it clearly meant more than anything to her, and we had to put it down. Really hit home 'cos we've got a 14yr old goldie too...had to go and get a drink...)
I have a friend who wanted to be a vet nurse, but fainted on the first day and has now gone to be a beautician!! She clearly REALLY wanted to work with animals, huh!
But yes, get a lot of varied work exp. I've done Kennels/cattery (where I work), a couple of vets (one of which was a small animal hosp, the other was a mixed practice), a cattle market, sheep farm for lambing, also helped with the small beef herd at the sheep farm, went to Vetsix too etc...i think variety is the key. Also, get good references!!