The KWPN, the international Dutch Warmblood registry, offers a particularly interesting program which evaluates the predisposition of a horse to produce offspring with OCDs.
Historically, the KWPN required x-rays as part of its PROK and Elite predicates. As a result, they compiled quite a database of multi-generational x-ray results – which could be compared against the horses’ pedigrees. So, a horse’s D-OC results are a comparison of the genetic quality of the horse against other horses in the KWPN database. All they are essentially saying is whether that horse has a higher or lower chance of passing OCDs onto his or her offspring. The only horses eligible for this evaluation are horses with bloodlines sufficiently related to the KWPN baseline population that this analysis is statistically significant.
The KWPN also provides OC Breeding Values scores for stallions, which take into account the D-OC scores and PROK results from that stallion’s offspring. These Breeding Values include reliability scores, which are meant to relate the accuracy (or reliability!) of the score.
Context is important. On the highest end of the range I have ever seen, a score of 108 was awarded to Sabantha Fortuna, our broodmare by Voltaire. This makes sense, as Voltaire had the reputation of producing horses with lasting soundness in their joints. On the lowest end in the KWPN database, Arko III currently has an 87 with a reliability of 66%, while Vigo D’Arsouilles has a 89 with a 71% reliability factor. Truthfully, however, most horses seem to land within a range somewhere between 99 and 101.
Think of the D-OC score as just another tool in your kit for producing sporthorses. Genetics are only one component to OCDs; environment factors heavily into whether a foal will be born with OCDs, or whether they will heal in that young horse. There are a great many things a fantastic stallion can bring, even if he has low OCD scores, so consider choosing a mare with high D-OC scores for him rather than eliminating him altogether.