According to an ongoing international study led by a New Zealand-based researcher, exercising Thoroughbreds younger than 18 months of age doesn't seem create make more--or fewer--cartilage defects in the intercarpal (knee) joints. It also doesn't make them more or less severe, and it doesn't change the sites on the joint where they show up. In other words, whether it's on the track or in the pasture, the exercise these foals are getting is going to cause exactly the same kind of wear and tear on their young knees.
"One thing is clear: even at a young age, Thoroughbred horses can present with numerous cartilage and hidden abnormalities that might go easily undetected for several years," said Woong Kim, PhD, researcher in the tissue mechanics laboratory in the University of Auckland Faculty of Engineering. "Another astounding fact is that these changes are likely to be caused by self-imposed activities by the animals themselves."
In their study, Kim and his colleagues divided 3-week-old Thoroughbreds into two study groups: those on an on-track conditioning program and those on pasture only. Foals in the conditioning group were trained (with their mothers) on an oval track five days a week over a distance of 1,130 yards (about 0.6 miles) per day. The rest of the time they were kept at pasture, like the pasture-only group.
After 18 months, six yearlings from each study group were euthanized so researchers could fully evaluate the animals' knee joints. "Approximately 700 horses per year die in the U.S. alone from catastrophic skeletal fractures while racing, and that figure does not include fatalities during training sessions," Kim said. "Thus, we made a careful decision, under the supervision of an ethics committee, that a small number of animals would be sacrificed for a 12-year study that involves more than 20 researchers across five institutions, generating more than 10 high-impact studies" in hopes of finding a way to reduce the number of racing-related deaths.
Extensive microscopic analyses of euthanized horses' (from both the exercise and the pasture groups) bone tissues revealed extensive information about the way equine knee joints react to the stress of exercise and how those reactions develop, Kim said. In particular, the researchers investigated cartilage thickening and defects and the rerouting of blood vessels into affected areas of bone. But interestingly, the researchers concluded that the number and severity of defects was not significantly different between groups.
"Our studies have provided graphical evidence showing that occult abnormalities can exist regardless of age and exercise," Kim said.
Interestingly, the horses in the conditioning group which were not euthanized and went on to a racing career had better racing results than the pasture-only group, Kim added. However, many factors than just the health of the knee joints play a role in that effect.
"Our study is a small piece of a big puzzle," Kim said. "Although several studies have reported that early conditioning causes no harm to the animals that receive it, this project is at a preliminary stage and requires further research."
The study, "Histologic and histomorphometric evaluation of midcarpal joint defects in Thoroughbreds raised with and without early conditioning exercise," appeared in the April 2012 issue of the American Journal of Veterinary Medicine. The abstract can be viewed online.
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