I've heard of people doing this with livestock, but not with house pets. I believe they use rubber bands on some dogs to dock their tails, though. They do use rubber bands to remove extra fingers from humans, as well. If a child is born with polydactyly (pronounced pah-lee-dak-til-lee), they can use a rubber band to remove the extra digit sometimes. The only kind that I know they use this for is an extra "thumb" branchin off of the first thumb. Young organisms don't remember pain when they are little, so it's best to do these things when they are younger, like almost newborns. They don't castrate baby sheep/goats that early, though.