The KWPN randomly select foals and has them x-rayed at the age of 11-14 months. The OC-index has a medium of 100. A score below 100 indicates that x-rayed foals have displayed OC-findings, whereas a score above 100 means that less or no findings have been documented. Each index comes with a reliability percentage, only published when that figure is above 55%.
The KWPN society normally refuses to licence stallions with a severe OC-remark, except when they show exceptional talent and potential.
Recent additions to the OC-index are the 2007 born stallions Bordeaux (by United x Gribaldi) and Bretton Woods (by Johnson x De Niro x Romancier). According to the KWPN society Bordeaux has an OC-remark, class C, on his right hind leg hock. However when vetted for the Swedish warmblood society the bay stallion was found to be clear. Bretton Woods has a class C remark on right hind leg hock and stifle.
Bretton Woods has an OC-index of 96, with a reliability of 63%. This can be considered a clear indication towards heritability of OC. Bordeaux has an OC-index of 101, 64% reliability, which means he neither improves the status nor burdens his offspring with heritable OC.