Grass-cracks or something worse? Cracked hooves in horses explained

Cracks in horses hooves are always a bit of a worry. But while some are fairly benign others can be serious. In this blog one of our equine vet bloggers takes a deeper look at horses hooves and the reasons for those frustrating cracks and fissures.
Structure and function of the hoof
The hoof wall or horn is made of keratin a tough protein with a low water content that is incredibly strong and also insensitive much like our nails. Its main function is to bear the weight of the horse while protecting the sensitive structures that lie beneath it. Such as the pedal bone as well as tendons and soft tissue.

The inside of the hoof wall is lined by sensitive laminae which act as a type of biological Velcro to attach the pedal bone to the hoof as well as acting as a pathway or conduit along which the new horn grows. The horn is produced by specialised cells called papillae at the top of the hoof wall the coronary band. The hoof wall grows on average at a rate of 610mm a month. This means that it takes approximately 912 months for a hoof to grow from the coronary band to the sole.
Types of crack
The hoof wall is subject to huge forces when the horse is at rest and even more so at exercise or whilst jumping. Overgrown or weakened hooves or those subjected to abnormal stresses can be more prone to splitting or breaking. 
The two most common types of cracks seen in the hoof are usually referred to as grass cracks and sand cracks. Grass cracks are those that originate at the bottom or sole of the foot. While sand cracks are those that start at the top of the hoof or the coronary band. Either of these may be complete or incomplete. 
In general grass cracks occur when the hoof wall is overgrown and begins to flare at the sole
These are rarely involved in severe lameness unless infection is present. 
Sand cracks are present at the front of the hoof extending from the coronary band. Those that occupy the side of the hoof wall are usually referred to as quarter cracks. 
Sand cracks are most commonly caused by poor foot balance
Quarter cracks are usually associated with a mediolateral side to side foot imbalance or with sheared heels. If you watch your horse walking it may be possible