Tough As Nails, of course! Tough As Nails is a premium hoof supplement for horses that promotes strong, healthy hoof growth in a number of ways. First, and what tends to be most important to horse owners, is the level of biotin in this supplement, which has been shown through research to improve healthy hoof growth. Tough As Nails increases a horse’s sulfur containing amino acid intake, which supports improved hoof growth, and has an increased level of calcium, which is an important mineral involved in the cross-linking of hoof proteins. Finally, the use of more bioavailable organic trace minerals, like copper and zinc, help develop and maintain a healthy hoof structure.