A free choice blend of calcium/phosphorus can help your horse balance out what [might be] missing from his feed. Also try mixing bentonite clay (montmorillonite or calcium pascolite) with distilled H2O into a mud thickness and packing the clean hooves with the mud. I place the hoof on a piece of brown paper bag and cut it out.
After packing the hoof with the clay I press in the paper bag. This will keep the shavings and muck out of the hoof till the clay dries and drops out. The clay draws out fungus. Spraying a mix of oregano oil and water onto the hoof also works well to kill fungus. I take in rescues and find this helps to improve the foot.
Source: Sheila Ryan, via LinkedIn Group “Horse Lovers of the Business World”