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