Hoof wall separation disease (HWSD) is a genetic defect in Connemara ponies characterised 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 caused by a frameshift mutation in the gene SERPINB11, (c.504_505insC), and 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.
Since 2016 all registered Connemaras are required to be tested and the result is included in their passports. If the relevant page has been removed from a Connemara Pony's passports or if the pony has been re-issued with a clean "white" passport, neither the prospective purchaser, nor her/his vet, will be aware of the pony's HWSD status. Where there is any doubt, the pony can be tested for the recessive gene prior to purchase (hair sample) at a cost of around £35.
Further information on the disease is available in this open access research paper.