Many of the hoof dressings on the market are, in effect, moisturizers. People often tend to apply them to hooves that look dry, yet are actually overly hydrated. In fact, the equine hoof is stronger and more resilient when it is dry. The moisturizing agent clings to and becomes trapped within the fault, undermining the hoof. Many of these products will tend to trap dirt, fecal matter, moisture, etc., which can create, or, more likely, exacerbate problems.
Child says that is especially true when dealing with cracked hooves.
Your climate and the general condition of your individual horse's feet will influence what kind of preparation will do the most good. You want to keep the hooves from getting too soft. A product with a petroleum base will repel water and seal the hoof capsule so the hooves don't get so wet and spongy. Keratex Hoof Gel is one product that protects the whole hoof capsule. Hooves often tend to crack more during the summer because of constant changes in the hoof's moisture content.