One of the major challenges in training racehorses is keeping them sound. Not unlike a human athlete, a racehorse's ligaments, tendons, bones and joints are susceptible to injury throughout its career and, at times, it seems impossible to avoid some sort of musculoskeletal mishap.
A vast number of components
can comprise any musculoskeletal injury but many believe the economics
of the Thoroughbred industry - namely the preparation of young horses
for 2-year-old sales and racing 2-year-olds - are the main culprits for
these sorts of injuries.
Training for most race horses commences when
they are 18 to 20 months old. The skeleton of a horse often does not
reach full maturity until they are four years old so training at a young
age might predispose horses to a multitude of career-limiting or
-ending injuries.
Shin soreness or bucked shins is an extremely
common condition in young racing Thoroughbreds and Quarter Horses (and
occasionally Standardbreds.) It involves the front portion of the cannon
or metacarpal bone and is the result of rapid bone modeling.
Before a
horse begins training, its cannon bones have the same thickness all the
way around. When horses start galloping, there is a considerable
increase in stress on the front of the cannon bone. To contend with the
stress, the equine body responds by adding new bone to the area in
duress. Ultimately, this creates stronger bones but early on this new
bone is prone to microfractures similar to the stress fractures that
human athletes endure during training.
The severity of bucked shins
can vary greatly, but most horses will exhibit pain when the cannon bone
area is massaged, will be lame while trotting, and have a short, choppy
stride. Another symptom is swelling in this area of the leg.
The
condition is usually diagnosed by recognizing the clinical indicators in
a horse when it begins its first training and/or racing campaign.
Horses suffering from shin soreness must be rested until all signs of
lameness have disappeared, which can take several days or many months.
For
example, New York-based trainer Barclay Tagg's then 2-year-old colt,
Tale of Ekati, had sore shins and returned after a month of light
training to triumph in the Grade 2, $250,000 Belmont Futurity on
September 15th of last year.
"One shin was very sore, but he got over it very quickly," Tagg said. "I got two real good works into him."
While
Maimonides, a 2-year-old, owned by Ahmed Zayat, exited the Grade 1
Hopeful Stakes held at Saratoga Race Course on September 3 with the same
affliction, his recovery was expected to take a bit longer. Sonny
Sonbol, Zayat's racing manager, said he needed "three to four weeks to
get over his shins and start back training and get ready for the
winter."
Estimates vary, but it is believed between 65 and 90 percent
of all Thoroughbreds in the United States and more than 40 percent of
all Thoroughbreds in Australia buck their shins early in training.
About
only 12 percent of young English racehorses buck their shins. Unlike
the United States and Australia, much less emphasis is placed on
2-year-old racing in England and English horses are trained on straight
tracks, so less strain would be placed on the cannon bone.
However,
the English are not immune to their young horses being injured. In a
study of 314 young Thoroughbreds in Newmarket more than 50 percent
experienced some period of lameness, and in roughly 20 percent of those
horses, the lameness prevented them from racing.
Also, bucked shins
are not exclusively relegated to 2-year-olds but to all horses which are
just beginning intense training. Some horses can suffer recurrences of
shin soreness after a period of stall of paddock rest. Therefore, bucked
shins do not discriminate based on the age of a horse, but depend on
how intense the training is and if the horse is undertaking the action
for the first time.
Dr. David Nunamaker, VMD, PhD, is an orthopedic
surgeon and chair of the research department at the University of
Pennsylvania's New Bolton Center who had conducted extensive research on
bone development from 1982 to the present. Dr. Nunamaker, Dr. William
Moyer, DVM, chair of the Large Animal and Surgery Department at Texas
A&M University and Dr. John Fisher, DVM, an equine veterinarian and
Maryland horse trainer, analyzed their research results and established a
training system created to reduce the severity of bucked shins or erase
them.
"We found that a horse's bone shape alters in response to its
training," Dr. Nunamaker said. "The way most conventional training is
conducted, a bone changes in a way it should not and that is why you get
into trouble with bucked shins. Also saucer fractures seem to occur
only in horses that have previously bucked their shins. This could lead
to catastrophic fracture."
Dr. Nunamaker concluded a problem will
become evident after 50,000 cycles of trotting and galloping. A cycle is
equal to one swift stride.
"The Standardbred doesn't have issues
with bucked shins because you never see a pacer do anything but pace
while Thoroughbreds train with a variety of gaits, such as walking,
trotting and galloping," Dr. Nunamaker said. "Thoroughbreds do not run
while they are training and when they do run it's only every 10 to 14
days. The bone remodels to what it experiences - which is not racing."
Speed
work is very important because when a horse runs at speed, the angle of
strain is much greater. So horses that breeze more often remodel their
bones for racing.
Utilizing the research results, Dr. John Fisher adheres to a training program that stresses and stimulates the cannon gradually.
"When
a horse is breezed, the bone sees it as an emergency and immediately
begins laying down new bone," Dr. Fisher said. "This new bone is weak
and needs to be strengthened through later remodeling, which would be
triggered by further breezes spaced closer together. If remodeling is
not allowed to take place and the horse is asked to do too much before
he is ready, the new bone will be weak and prone to injury. The
bone-strengthening is entirely based on stress and recovery to gradually
increase bone density and strength."
In Dr. Fisher's program, horses
transition from a one furlong work at 15 seconds to a half-mile or more
in 13 seconds over a 16-week period.
If there are more than four
days between short distance works, Drs. Nunamaker and Fisher have
discovered the new bone will stop rebuilding and actually weaken, with
no additional stress after five days.
Once the program has been
finished, a horse is prepared to begin conventional training because he
should have accumulated enough bone strength that he will not buck
shins. However, if a horse is subjected to different track conditions or
circumferences, such as a European horse racing on American dirt, the
threat of shin soreness resurfaces.
Even though Dr. Fisher has
modified the program throughout the years, he is still quite pleased
with its performance.
"We just don't have many injuries at all," Dr
Fisher said. "No more tendons, no more suspensories, no more fractures."
How
much high-speed work and distance are required to signal the bone to
remodel itself correctly and not form weaker bone? Research is still
being conducted but Dr. Nunamaker claims the goal is to correctly change
the bone at the slowest possible speed over the shortest possible
distance.
"Maybe two furlongs, maybe one furlong," Dr. Nunamaker said.
"Maybe it won't even have to be that far. We just don't know but there
is a fine line during a crucial time period as to what is too much and
what is not enough."
Once the bone has attained maximum strength by becoming thicker at its stress points, it should stay that way.
"When
we looked at the timing of the injuries that occurred in horses that
have shin injuries, we found that when the horse reached four years old,
it no longer had shin injuries," Dr. Nunamaker said. "It may develop
injuries to other parts of its body, but not to the shins. It is in the
first two years of its training program, if it starts at two years of
age, that it is going to have shin injury problems. After that no more
shin injuries."
It is important to note the bones are the slowest
part of the body to train. In most cases, the cardiovascular system and
soft tissues are prepared for the stress of racing before the bones.
Study
results presented at the 2005 Australian Veterinary Association depict
shin soreness or bucked shins can be avoided. Certain training
techniques place horses at risk for this condition.
The most
significant factor was how far the horse trained and how quickly he
went. If a horse trained at a speed greater than 33 mph during its first
ten weeks of training, he tended to have some shin pain.
"A gradual
increase in the weekly distances at these speeds is the key to reducing
the number of cases," Dr. David Evans, BVSc, PhD and associate professor
of veterinary science at the University of Sydney and one of the
researchers on the project, said.
The study also revealed that using
short gallops of 200-300 meters at 33 mph or greater can decrease shin
soreness; training horses to induce shin soreness will not reduce the
risk of contracting the condition during subsequent training; and shin
pain occurred much less often in horses that began training at an
average age of 30 months.
Dr. Evans acknowledged that much more research was necessary before any authoritative program could be implemented.
K.L.P.
Verheyen, DVM, MSc, PhD, MRCVS, of the Royal Veterinary College (RVC)
in London, agrees with Drs. Nunamaker and Evans that training methods
are associated with injury risk.
"Stress injuries are repetitive
loading injuries," Dr. Verheyen said. "Compare it to a paper clip and if
you keep bending it, it will break. Interval training (alternate
periods of hard exertion and rest) is a better option because high-speed
exercise is as not bad as previously thought. It actually stimulates
bone to respond, because bone is a living tissue and is constantly
remodeling. If the same exercise is repeated again and again, the bone
will stop responding, which is what we think is happening with the
low-speed exercise and stress fractures."
While more research must be
conducted to provide greater insight into how equine bones adapt and
grow, even less is known about how tendons and ligaments respond to
training. In a series of recent studies, Allan Goodrich, a professor at
the Royal Veterinary College and the University College of London,
discovered that the tendons of young horses (less than two years)
strengthen in response to training. These results raise the possibility
that early training enhances the development of the limb's support
structures and could diminish injuries during training and racing.
After
reviewing training methods and treatments, it is obvious much more
research must be completed before any sound strength management program
can be introduced.
"We just don't have all the answers yet," Dr. Nunamaker said.