Try to get a job with a vet, volunteer in roles that allow you to work with animals, just get a feel of what its like. I started off wanting to do a degree in speech pathology and went to volunteer with a special school. After 6 months, I realised that my problem with needles meant I was not going to get anywhere close to becoming a speech pathologist and that my interest was really in teaching special ed. After a short trip to East Timor, I realized I wanted to learn how to use technology to help people with special needs live and work to the best of their abilities. So, my point is, volunteering will let you know if that is indeed something you want to do or if there's another path somewhere you haven't thought of that you really want instead.

As for the pre-requisites, maybe while volunteering, you can go over the materials using various universities' OpenCourseWare classes and syllabuses until you know for sure that you want to get into this? This way, when its time to go do the undergrad classes, you will at least know the stuff and hopefully, that'll allow you to take a heavier courseload and finish faster? I use both MIT and University of Utah OpenCourseWare, there are plenty out there, so do Google.

I hope you find a satisfying career path. At least you get to tell people that you've really seen and done different things.