Do they shear the sheep or kill them for Uggs?

I can't imagine what they would benefit from killing the sheep. I mean, I guess it'd be easier to make the boots, then, but you'd have to buy more sheep. If they only sheared them, then the wool or fur or whatever would grow back, right? But idk, it is called sheepSKIN. People are telling me that they kill the sheep, so sorry if the question sounds shallow and stupid. :3 I'd just like to wear my Uggs without feeling like I'm walking in mutton. ;D