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Current understanding of osteochondrosis

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Page 1: Current understanding of osteochondrosis

Current understanding of osteochondrosis Dr. Leo leffcott thinks that the underlying or primary lesion of osteochondro­

sis (OC) arises as a failure of endochondral ossification in the articular growth cartilage which can then extend to more serious pathology and the typical signs of Oc. "There is much research currently underway in laboratories around the world attempting to unravel the complexities of pathogenesis of the condition," he said in an interview recently. .

He said there is a well-known genetic component to this condition although this is only part of the story as the problem has many causative factors. The breeding of horses in relation to OC is important, but should be put into its proper context. "I think management and environmental factors are probably more relevant to many stud managers. It is quite clear from our research that overfeeding is something a lot of horse people tend to do because horses are being bred for sale:' He pointed out that it is very important that horses are not overfed and that there are very sensible and easy methods of checking this, like weighing foals before and after weaning. Limiting the foal's growth rate to a reasonable level will limit the chances of things going wrong within the growth cartilage and the consequential development from dyschondroplasia into osteochondritis dissecans (OCD).

"We've heard a lot about mineral supplementation and getting the calcium:phosphorus ratio right is an important factor in preventing the development of OC," he said. "Another thing from a stud management point of view is the thought that copper deficiency is related to the incidence of Oc. Some studies done about 10 years ago at Ohio State University has given the impression that copper deficiency is involved in OCD. Work that we have done, as well as recent research in New Zealand, has shown that this is probably not the case. Perhaps other parts of the developmental orthopedic disease syndrome may be sensitive to copper but it is a controversial area that needs more work. If we follow the research that is happening in New Zealand at the moment, then we probably shouldn't be recommending as much use of copper as we have been doing recently."

Another factor, mentioned by Dr. leffcott, that is extremely important in limiting OC, is the effect of exercise on young horses. "We see OC commonly in Thoroughbreds, Standardbreds, Arabians and other large breeds but we very rarely see it in ponies and very rarely, if at all, in feral species, for example zebras. Feral species are up and about and moving soon after they are born and they get an awful lot more exercise than domestic horses often do."

Some studies that were done in Holland showing that animals exercised when they were younger than 5 months old were less likely to suffer the effects of Oc. If you exercise foals before they are going to show early lesions in the growth cartilage, then this exercise should stimulate cartilage and bone and improve the integrity of the joints and articular surfaces, which means horses are less likely to develop Oc. However if you start exercising foals after they've got these early lesions, that is, when they are yearlings or older, then these early lesions are probably going to be exacerbated by exercise and the horse will most likely develop full-blown OCD. Another point about exercising horses younger is that it will stimulate tendon and bone development. We see so many horses that end their performance careers due to lameness, so anything that will stimulate modelling of bone and improve skeletal integrity in the first year of life is extremely important.

"There are a number of valuable preventative measures that stud managers can do to limit OCD, but without understanding more about the pathogenesis we are not going to eliminate it completely," Dr. leffcott said.

Can too much exercise cause osteochondrosis?

At Colorado State University, Dr. Robert W. Norrdin and his team are con­ducting a study entitled, "Role of strain alignment and microdamage in the subchondral bone failure of osteochondrosis." Bone and joint injury can occur in a horse, regardless of its activity level. However, these problems appear more frequently in performance horses, especially intensively trained Quarter horse and Thoroughbred racehorses.

Volume 20, Number 5, 2000

From RIRDC Equine Research News (1/00)

OCD is a defect in the cartilage and bone of the joint surfaces in the legs. Microscopic damage usually occurs in the bone before the cartilage collapses. The most severe forms of the disorder can result in lameness. OCD may be caused by strain and overuse of the leg joints as well as traumatic overload as the hooves continually strike the ground with excessive force. "Horses develop unusually high stresses on joints during training and racing," states Dr. Norrdin. "We hypothesize that compressive strain on the fetlock jOint is primarily responsible for the accumulated damage that often leads to bone failure in performance horses." Early results of this study indicate that although the pattern of the strain on the bone is not always consistent between affected horses, excessive strain on the joints is traumatic and does playa role in equine bone failure. According to these investigators there may be scientific jus­tification for altering training schedules, modifying shoeing practices, and adjust­ing track surfaces to protect performance horses from such injury.

This one-year investigation is a collab­orative effort between Colorado State University and the University of Califor­nia, Davis, funded by the Morris Animal Foundation.

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