I have a paint with the most horrible brittle feet in the world, and literally got my tail chewed for their condition the last time the farrier was out to re-set him. He said that the problem that we're having with brittle hooves right now is that its just so dang dry here in Texas. Fertilizer or not. The paint is on a biotin suppliment (Farrier's Formula), and he said that will help wth brittle hooves, but that I would be better off in this dry weather using a hoof conditioner as the best bet right now against our weather and dry and brittle hooves. FWIW, I do think that fertilizer is drying to a horse's hooves, but only until it has been rained in.