Horn is the generic name for both the hoofs and horns of animals. In Dwarf Fortress, hoofs and horns are functionally identical once stripped from their previous owners. Both are obtained by butchering certain animals, although horns are often only present on the male members of a particular species. In certain cases horns may also be referred to as antlers, as is the case with elk.
They can either be carved into horn crafts, or used to decorate existing crafts at the Craftsdwarf's workshop. Doing so uses the bone carver labor.
Creatures with horns and hooves can be very formidable in combat, especially since most of them are several times larger than your average dwarf. They have the ability to cave skulls or bruise internal organs. It is best to approach all hoof/horn wielding creatures with caution.
It seems that bone carving skill doesn't empower you to carve troll horns even in 44.05 version.
[IMPACT_YIELD:200000] used bone for all of these, no data