I noticed a barefoot horse I was bringing in had a couple of cracks in his hoof last week, and with the ground conditions changing so rapidly it’s not really surprising.
Cracks in the wall of the hoof can occur for numerous reasons, but good care helps eliminate the problem.
There are two main types of cracks; sand cracks and grass cracks. I learnt that an easy way to tell them apart is that a grass crack grows upwards, like grass growing up from the soil; and a sand crack grows downwards, like sand running down an hourglass.
Grass cracks tend to be superficial; thin and not penetrating very deep within the hoof wall. They occur when the ground conditions change from very wet to dry (such as in the last fortnight), due to poor nutrition as hoof growth is inhibited, and lack of exercise as exercise increases blood flow to the hoof. Horses aren’t usually lame due to a grass crack, but they should be treated by the farrier when he next comes. Applying hoof oil to a crack only locks moisture and bacteria in, so whilst hoof dressings have their purposes when used on unbroken feet, they shouldn’t be used on open areas. If an infection gets into the crack it can be very difficult to treat. The farrier may adjust his shoeing or trimming to support the crack, and if it is large and he or the vet are called as the horse is unlevel then they can repair the crack by either clipping it together with small pieces of metal, or filling it with a resin or polymer.
Sand cracks are caused for similar reasons to grass cracks; however, they originate from the coronary band and extend downward. The danger I was taught with sand cracks is that a piece of dirt can get lodged into the crack and cannot escape, so it becomes infected. In a grass crack, gravity with pull the intruder down and out, but the solid bottom of the sand crack traps it. Sand cracks can be treated by burning a horizontal groove at the base of the crack, to prevent it from growing deeper.
So whilst most cracks aren`t anything to worry about, it does imply that the feet are becoming brittle and in need of a farriers attention so that they are balanced and there are no stressed areas, which are predisposed to cracking. A hoof supplement can be fed to help strengthen the hooves in the long run, and your farrier may also recommend a hoof dressing; I use a tar-based dressing that comes highly recommended.