equine osteochondrosis

It makes sense to take all possible steps to reduce the risk of horses developing heritable and potentially performance-limiting diseases, like the developmental orthopedic disease osteochondrosis. But new study results suggest that a few osteochondrosis cases might be due to joint infections and, therefore, essentially out of our control.

If scientists can identify those particular cases of osteochondrosis, the affected horses could probably continue in the breeding programs without passing on “osteochondrosis genes,” the researchers said.

“It’s likely that several mechanisms may instigate the process (of osteochondrosis development), with sepsis and bacterial infection of cartilage canals being one of them,” said Bjørn Wormstrand, PhD candidate, of the Norwegian University of Life Sciences Faculty of Veterinary Medicine at the, in Oslo.

“As a nonheritable disease, this could be interesting regarding the breeding limitations imposed in some studbooks because of the heritable component in the development of osteochondrosis,” he said.

Osteochondrosis forms when growing cartilage, which ultimately turn to bone, loses blood supply in a small area. That small area, cut off from circulation, eventually dies and necrotizes. During that transformation, the area becomes an osteochondral lesion, which can lead to pain, lameness, and poor performance.

Scientists are still investigating the exact mechanisms that cause that growing cartilage to lose vascularization (blood supply). But several studies have shown that the process appears to be genetically linked, passing down within equine families, Wormstrand said. However, he and his fellow researchers suspected that in some cases of septic arthritis—which occurs when bacteria infects joints’ synovial space—bacteria might destroy vessels in the cartilage canals and interrupt blood supply. And in that situation, the genetics would have nothing to do with the resulting osteochondrosis.

In their study, Wormstrand and his colleagues dissected the joints of seven foals euthanized because of septic arthritis; all the foals had at least one osteochondral lesion. While pre-euthanasia tests had already revealed bacteria in the synovial fluid, Wormstrand’s group wanted to see if there was also bacteria in the growing cartilage near the joint.

Sure enough, they found bacteria in the foals’ cartilage canals, which guide the cartilage growth as it turns to bone, he said. They noticed that bacteria appeared to be related to the osteochondral lesions, causing necrosis of areas of cartilage fed by the infected canals. Those septic lesions occurred in the study foals’ articular-epiphyseal cartilage complex and physes (growth plates of bones forming from cartilage).

“Most osteochondral lesions in horses in general are not caused by sepsis (bacterial infection),” Wormstrand said. “But if one could distinguish the sepsis-related, presumably nonheritable osteochondral lesions from the lesions with a heritable component, these horses could possibly be used for breeding without increasing the frequency of osteochondrosis in the population.”

The study, “Septic Arthritis/Osteomyelitis May Lead to Osteochondrosis-Like Lesions in Foals,” was published in Veterinary Pathology. https://journals.sagepub.com/doi/abs/10.1177/0300985818777786