01/01/2025
[From 2020]
"Turning a horse out until its third birthday and then beginning race training will adapt the skeleton to turnout for a year, but not to training or racing. The bone modeling system will largely atrophy. The horse is then introduced to training and will have to recreate the vascular supply and cell population devoted to remodeling. By contrast, the horse who trained at two only had to repurpose the vasculature and cells already present for growth.
This can be complicated by the fact that the heart and lungs, which are oft-used indicators of a horse’s fitness, don’t respond to training exactly the same way as bone. Horses have such relatively large heart and lungs that they respond faster than the skeleton to training, especially when a previously sedentary horse begins training. Dr. Larry Bramlage believes the horse who went through a year of turnout and began training at three is at greater risk of skeletal injury down the road because its skeleton may be less able to keep up the pace. Thanks to heart and lung conditioning, the rested horse may appear to be getting fit just as quickly (or even moreso) than his stablemate who trained at two, which could fool a trainer into increasing his workload too quickly for the skeleton.
The data bears this out. Year after year, the Equine Injury Database has shown that 2-year-old runners had a significantly lower fatality rate than 3- and 4-year-olds. Preliminary data released earlier this year showed that older horses who had raced as 2-year-olds had a decreased risk of career-ending injury to those who had not."
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