In summary to the threads theat B. listed, most people use some form of dressing for cracked hooves. This wonderful stuff is available at farm feed stores. It is said that the lanolin content is what keeps the horn from cracking. The warranty sheet from HI says that some people use linseed oil for the same purpose.
I did find some stuff for waterproofing boots that had lanolin in it.
Hooflex smells bad until some of the "active ingredients" evaporates (usually overnight). But that was all that was available at the feed store. :barf:
Check out the threads, there's some good stuff there.