A late reply. An excellent method for softening hooves is found in Histo Logic (Sakura Finetek website) and written by Jane Chladny several years ago. Animal hooves are particularly diffiicult and she had a good method for doing horse and bovine hooves. Check the Histo Logic topics with key words, or author's name to access the protocol.
Gayle M. Callis
Histonet mailing list