Yes, skulls contain brain matter so are potentially infected with scrapie or MCD so they get minced up and incinerated. If for some reason you have to put down an animal on your own land and you have a suitable gun, well....... Insects would then clean out the skull. The horns would tend to fall off the core but that's what glue is for. That might work for a single sick animal, but you cannot go into business that way.