Well sure when you're holding the muzzle to the forehead a 22lr is pretty efficient, waste of bullets actually when you could just use a hammer or maul... That's what we used anyway when butchering on the farm. Worked better on hogs and a 22, they have a hard skull and if you hit them at wrong angle it just slides between bone and hide and they do not like that one bit...
Had a guy come out to buy a hog one time and was going to kill it and bleed it at our place and take it home to butcher. He insisted that he kill the hog with his 22, so fine... Shot it once right in the sweet spot and the hog screamed to bloody helll, shot it again and same result. My dad said, "let me see that gun" and checked the bullets only to find out it was bird shot... The hog got the maul next.