These are a really long lasting chew which are not as hard on teeth as things like Marrow Bones and Buffalo horns.  The Horn itself is very long lasting and becomes slightly softer when damp which helps to keep teeth healthy and prevent that damage associated with hard bones and solid chews but still maintains its shape and durability.  Some have marrow within which is highly nutritious and once they've manage to get it all out the space can be filled with treats and food for an ongoing enrichment activity toy