Bucking the strain of bucked shins - DVM
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Bucking the strain of bucked shins
Although fairly prevalent in 2-year-olds, this common inflammatory condition of the cannon bone can affect any Thoroughbred racehorse in training and lead to more serious injury further on in a horse's career.


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Prevention

According to Moyer, Fisher and Nunamaker,1,2 horses that train on a harder track surface seem to remodel their bone at a faster rate than horses exercised on a more compliant surface. Also, classically trained horses that exercise on a harder surface seem to have a higher incidence of bucked shins than horses training or racing on a more compliant surface.

Nunamaker suggested that an exercise regimen could be designed to optimize the shape of the MCIII. This in turn should influence (i.e., decrease) the incidence of bucked shins in the Thoroughbred racehorse model and diminish the problem within the industry. Noted Nunamaker, "Adaptive exercise has been shown to change the geometric properties of MCIII, to influence bone modeling and remodeling and to reduce the incidence of fatigue [bucked shins] of MCIII."1

If everyone followed the Nunamaker-Fisher program for training,1,2 there probably wouldn't be any bucked shins, states Hogan. "They figured out why horses get bucked shins and discovered that it's really a very simple phenomenon. They studied the physics of the way the horse's foot hits the ground and determined the best way to train young horses to help eliminate the condition."

Nunamaker found that increasing the number of short distance works (breezes) from once every seven to 10 days (as done with classical training programs) to three times a week produced large changes in the modeling, remodeling and inertial property measurements of MCIII.1 Some trainers may suggest that, mentally, it's difficult to get a 2-year-old to gallop out the last furlong a couple of times a week. Nunamaker and Fisher used sensors applied to the cannon bone and worked out the physics, coming up with the best training modality. Nunamaker showed with the modified training regimen that only 9.3 percent of the horses trained had bucked shins during the five-year training period when the modified training program was implemented. Compliance, then, is the issue.

To extrapolate from their work, Hogan suggests that when adding breezes to a young horse's schedule, at the end of their gallops once or twice weekly, push them the last furlong to run at a 12- to 13-second clip, so the bone gets the signal or request for higher speed that allows it to adapt to that kind of speed. "Then the bone is prepared for that increased speed as it begins to lay down strong lamellar bone. But in this scenario it has enough time to do so," he says.

Conclusion

As with most musculoskeletal injuries in the racehorses, an increased awareness and understanding of the physiologic requirements of bone's adaptation to modern training practices has led to the early detection of many stress-related injuries. Bucked shin syndrome is just a precursor to what could become a potentially deleterious breakdown in the microstructure of the cannon bone. Early recognition of the problem, coupled with the knowledge of how to use exercise judiciously to temper the changes occurring in the bone in response to training, has resulted in decreased morbidity and a properly-modeled cannon bone better suited for multiple years of safer competition. All good news for Rolling Fog.

Ed Kane, PhD, is a researcher and consultant in animal nutrition. He is an author on nutrition, physiology and veterinary medicine with a background in horses, pets and livestock. Kane is based in Seattle.

References

1. Nunamaker DM. On bucked shins. Milne Lecture: Equine Orthopedics, in Proceedings. American Association of Equine Practitioners, 2002;48-76.

2. Moyer W, Fisher JRS. Bucked shins: effects of differing track surfaces and proposed training regimens, in Proceedings. American Association of Equine Practitioners, 1992;541.


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Source: DVM360 MAGAZINE,
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