I got an interesting piece of advice from my current boss who is campus veterinarian where I go to school. He said I should not mention welfare in any way shape or form. I'm on the fence about this because I've learned and come to understand welfare from a variety of perspectives and production animal welfare in particular is an interest of mine. Also, I think "animal welfare" has evolved substantially since he applied what, 30 years ago?
My advice to you is to filter the advice you receive on this topic carefully
I think many different ways of writing and many different topics have been acceptable and helped people to gain admission but I think the bottom line is: make it your own, not just a patchwork of other peoples' ideas. Have lots of other people read your statement, too; it's really helpful and you get ideas/feedback you hadn't even thought of. Other people will be able to tell you if it draws them in or leaves them cold. Good luck