If you're not a fan of science, and if you're willing to work really, really, REALLY hard, law is your best bet. You have the ability to not only prosecute animal abusers, defend organizations such as PETA, Animal Lib etc, but also achieve change through the legal system - acquiring tougher penalties for animal abusers, being on the frontlines of arguing against factory farms etc. check out
http://www.voiceless.org.au/
The other option, which you'll have to wait some years for, is politics - something I'm pretty interested in. For instance, look at Senator Xenophon from South Australia. He got almost a billion dollars (from memory) for the Murray-Darling Basin - all because Kevin Rudd needed his vote in the Senate. However, imagine if instead of Senator Xenophon, one of us were there. For K.Rudd to "buy" our vote we may say, "ok kevin, I’ll pass this legislation IF you boycott the live trade and sow stalls within Australia." It's totally possible! I wouldn't mind doing this in say 20 years - however, I don‘t think I really have the capacity to gain heaps of votes. However, if we keep on pushing veganism so it becomes mainstream, it's entirely possible. If you interested in this get familiar with The Greens - they're most likely to support the causes you do:
http://www.greensmps.org.au/
Also of course have a chat to some of the people that work for Animals Australia. But yeh, like Apple Scruff said, pet shops and zoos really aren't a good place to look if you want to help animals - those places are suited more to people who wish to exploit them.