Two Decades of Equine Osteochondrosis Research Reviewed

Twenty-two years after a prominent equine veterinary researcher declared it a primary research focus, osteochondrosis—together with other orthopedic disorders of juvenile horses—is now the central topic of a special issue of the Veterinary Journal.

Leo Jeffcott, BVetMed, PhD, FRCVS, DVSc, MA, VetMedDr (h.c.), currently emeritus professor of clinical research and training and of equine practice at the University of Sydney Faculty of Veterinary Science in Australia, first made that declaration in a 1991 review paper in Equine Veterinary Journal. Osteochondrosis research has since progressed immensely, leading veterinarians to hope that the disease’s detrimental effects on equine health and breeding economics might be significantly reduced in the near future, said Paul René van Weeren, DVM, PhD, Dipl. ECVS, professor in the department of equine sciences at Utrecht University in the Netherlands. Van Weeren and Jeffcott coauthored a review of osteochondrosis included in the Veterinary Journal special issue. “There is little hope that osteochondrosis will be eliminated within the next 20 years

if we stick to the current breeding goals regarding performance and aesthetics,” he said. “But further progress in the knowledge of cellular and molecular mechanisms will certainly make the condition more manageable and hence reduce the impact on equine health and welfare.”

The “current breeding goals” van Weeren mentioned include preserving the genetic traits of a specific performance or physical appearance rather than eliminating traits that might cause osteochondrosis, he said. However, that’s in part because researchers have yet to pinpoint how a horse passes osteochondrosis on to its foal, and the disease sometimes skips a generation. Until scientists are better able to determine which genes are responsible for osteochondrosis and how the genetic transfer occurs, researchers cannot make specific breeding recommendations.

“In any case there is little hope of eradicating the problem by breeding strategies alone, as environmental factors are known to play a large role and because the disease is definitely polygenic (involving multiple genes),” he said.

Researchers have learned much in the past 20 years about what appears to increase the risk of osteochondrosis and how it develops. For example, they now know that large pastures can be a risk factor for young foals, as can a lack of exercise and even slight changes in blood supply through tiny arteries in a foal’s cartilage. Scientists have also determined that copper deficiencies might not cause the disorder but supplementing mares with copper in late pregnancy can benefit their foals' future cartilage health.

Van Weeren said researchers also have made progress in treatment, recognizing that osteochondrosis with bone fragments can be easily and successfully remedied via arthroscopic surgery, while osteochondrosis without fragments doesn’t usually require surgery. And if it weren’t for the economic value of a clean radiograph (X ray) at a young horse sale, treatment might not be worthwhile in many cases at all, as the condition frequently resolves spontaneously.

There’s also been significant evolution in what to call the disease and what the disease actually is. These have been among the many sources of controversy surrounding this condition over the past several decades, van Weeren said. Coined osteochondritis dissecans in 1887 by German surgeon Franz König, researchers have finally been able to create names for the complex and varied condition that more accurately reflect what it is. Now osteochondritis dissecans (OCD) is reserved primarily for cases where there are actual loose fragments and obvious inflammation. When there are no fragments or inflammation, it’s called osteochondrosis (OC). A new term surfaced just this year—juvenile osteochondral conditions (JOCC)—which groups together all developmental disorders related to immature joints or growth plates in young horses, he said. And the 1986 term developmental orthopedic disease (DOD) is still valid as well. First introduced by Wayne McIlwraith, BVSc, FRCVS, PhD, Dipl. ACVS, Dipl. ECVS, professor of surgery and director of Colorado State University’s Orthopedic Research Center, DOD now serves as the broader term referring to all the above conditions plus other orthopedic disorders related to development, such as Wobbler syndrome and limb deformities.

Although scientists have responded to Jeffcott’s call 22 years ago for heavily focused osteochondrosis research, they still have a long way to go in understanding this complex disease, van Weeren said. New studies will focus on further localizing the responsible genes on the equine genome and developing a clearer picture of how the various forms of osteochondrosis are linked.

Van Weeren's and Jeffcott's review, "Problems and pointers in osteochondrosis: Twenty years on," will appear in the Veterinary Journal

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.