Many horses develop hoof cracks at some point in their lives. Most are innocuous and resolve themselves with good nutrition and consistent farrier care. But there are many types of hoof cracks, and sometimes you'll need to take extra steps to make sure the crack 'heals' and no new cracks develop. These are serious, and they need to be treated.
As with any horse problem, the first thing you need to ask yourself is "why is this problem happening?" Because horse's hooves grow at a slow rate, about one centimeter (slightly less than 1/2 inch) per month, hoof cracks can take a long time to grow out once they get started. Finding the answer to the question is less time consuming, expensive, and frustrating than just trying different random solutions.
Hoof cracks are named for the area of the hoof they are located, or the suspected cause: quarter cracks, heel cracks, toe cracks, sand cracks, bar cracks, and grass cracks.
There are many reasons why hoof cracks form. Nutritional deficiencies can cause fine cracks on all four hooves. The hoof walls may be thin or weak, slow-growing, show ridged horizontal rings, and the free edge of the hoof may chip easily.
In very wet or dry conditions hooves can weaken, especially if the horse is exposed to extremes such as wet-then-frozen ground, or wet-then-very-hard, dry surfaces. Some moisture is good for hooves, but continually standing in muddy, wet conditions or soggy bedding and wet manure can make the hoof material expand and weaken.
Hard surfaces can be a problem for horses ridden barefoot over rocky or paved surfaces. Hooves can chip and wear if horses have to travel over these surfaces frequently. Some hoof protection, either a shoe or boot, can help prevent these types of cracks.
Hoof cracks can travel horizontally or vertically. Horizontal cracks and lines on all four hooves may be a sign of nutritional deficiencies. Short horizontal cracks may indicate a hoof abscess has erupted through the coronet band at the top of the hoof. As the hoof grows out, the crack grows down the hoof. As it reaches the free edge, it may cause the hoof to chip.
If only one foot is affected, nutritional deficiencies can be ruled out. If only the front hooves are involved, suspect concussion cracks from hard surfaces. If the horse is traveling over hard surfaces a lot, then back hooves may also crack. Cracks in the front hooves may also be a sign of contracted heels.
Quarter and sand cracks near the heel of the hooves may be an indication of poorly trimmed hooves. If the heels get "run under" or shallow, the hoof wall may crack due to uneven weight distribution. This too may indicate that contracted heels are developing.
If the hooves are chipping, it may indicate that the horse frequently travels over rough or abrasive surfaces such as rock or gravel, frozen mud, or ice. Although hoof material is very strong, it is still not as hard as stone or pavement. Horses that must travel on these surfaces need some protection.
Some cracks are caused by an injury at the coronet band either by a direct hit or by repeated concussion over hard surfaces. Cracks and chips can also form if the hoof is left untrimmed. White-line disease—an infection that sets in between the hoof wall and underlying hoof structures—may cause the hoof to split, crack, or chip.
If wet, dry, or very hard conditions are to blame, you may have to change the horse's environment. If mud or wet is a problem your horse may have to spend at least part of the day on a dry surface like wood pellets or dry sand that will help draw moisture out. If dry conditions are the problem, many people let their water troughs run over, forming a damp area that the horse must stand in to drink. Hoof oils may not help as these products may seal out moisture. In extreme cases, where hoof cracks are affecting the horse's soundness, shoes, staples or other supportive materials may be necessary to reinforce the hoof as the hoof crack heals. If laminitis or a severe infection is involved, a veterinarian can prescribe treatment options such as antibiotics.
Balanced trims by a good farrier and good nutrition are the cornerstones of good hoof health. If the horse must travel over rough surfaces such as roads, gravel, rocks, or ice consider using either shoes or hoof boots. Some horses will "toughen up" if exposed gradually to these surfaces, but some may always stay sensitive and need some extra protection. It's important to realize that, because hooves grow relatively slowly, repairing cracks can be a long slow process.