(from U.C. Davis website) “Hoof Wall Separation Disease (HWSD) is a genetic defect characterized by a hoof wall that easily breaks and cracks, and a normal appearing coronary band. The breaks and cracks begin to occur in young ponies. In severe cases the pony bears weight entirely on the sole of the foot which can lead to severe lameness. HWSD is inherited as an autosomal recessive trait. This means that carriers are completely normal and only animals with two copies of the mutation will show clinical signs of the disease. HWSD appears to occur only in the Connemara pony and the carrier frequency has been estimated to be about 14.8%. A DNA test for this specific mutation can determine if ponies are normal or if they carry one or two copies of the mutation. Ponies that carry two copies of the mutation are highly likely to be affected with the disease. Some cases are milder while others are more severe. We have identified at least one case where the pony does not appear to have clinical signs associated with having two copies of the mutation. This indicates that the mutation is not fully penetrant; however it has very high penetrance of 96.8%.