She's a good age at 8. Are you sure the weight gain is down to the straw or could it be an underlying health issue? My boy is an older Bun and he has similar issues with his rear end. I have to clean him up sometimes now, but I think it's because he's an older boy and may be arthritic. I've just accepted that's the way he is now and as long as he's enjoying his life, that's fine by me.