Lameness in Racehorses Paul R Earl Facultad de Ciencias Biol

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Lameness in RacehorsesPaul R EarlFacultad de
Ciencias BiológicasUniversidad Autónoma de Nuevo
LeónSan Nicolás, NL 66451, Mexico
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Millions and millions of dollars are involved in
horse lameness. It is caused mainly by
overexercise on hard surfaces.The first point
is that 70 of horses on dirt tracks have front
cannon bone problems, whereas 4.1 times less
(17) on turf tracks have. The cannon bone is the
main fused leg bone. The second point is that
maturity is reached at 4-5 years of age, and
young bones are soft. This is an appeal for all
racetracks to switch from dirt to grass.
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Racehorses run farther as they get older,
staring at ¼ or 3/8th of a mile (3 furlongs)
going to 2 miles usually. Nonetheless, it is
speed not distance that causes the damage. Still,
the owner of Man o War at 3 years old winning
the Preakness at 1 ¼ and the Belmont Stakes at 1
½ miles thought the Kentuky Derby at a 1 1/8
miles was too long for him!There is more to it
than if stake winners only. Some owners only want
to win stake races. Then those horses that cannot
reach a Gallant Fox triple crown standard will
be sold or crippled or both.
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The main sign of trouble ahead is heat in the
legs.
Infrared thermogram. What is your diagnosis?
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The anatomy of the legs
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Some Problems with the HoovesSubsolar
Infections are the commonest hoof infections, and
common causes of acute lameness. A penetrating
wound in the sole, frog or white line generally
caused by the horse stepping on a sharp object
like a nail causing lacerations.Bruised Soles
are one of the most common causes of lameness in
both shod and unshod horses. Injury to the sole
may cause damage to the sensitive structures
underneath and results in bruising. The result
can be damage to the many tiny blood vessels
underneath the sole and consequent hemorrhage.
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Normal and contracted heels
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Splints that were parts of the toes millions of
years ago can make a horse from 2 to 3 years
lame. The ligament between each side
bone--splint--and the cannon bone fuse possibly
causing a temporary soreness.Bucked shins is a
very common condition possibly caused by
microfractures and the like caused in turn by
concussion and stress. The surface, the
periosteum, may separate from the front of the
cannon bone in the process of laying down more
bone. Many trainers force the horse to buck as
inevitable. This is done by fast works, not
galloping long distances. This scale is walk,
jog or trot, gallop, breeze, work or race.
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Desmitis of Supporting Ligaments like the with
impar ligament and the proximal suspensory
ligament desmitis is a separate diagnosis from
navicular disease. Will some of these lame horses
develop inflammation and degeneration of the
navicular bone? Such horses are separated from
those with abnormal fluid in the navicular bone,
although a few horses have both fluid in the bone
and desmitis of the supporting ligaments. These
horses are diagnosed with navicular disease. The
treatment is the same, mainly depending on
rest..
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Thrush is an infective condition of the frog and
its sulci which results in degeneration of the
horn and the production of foul smelling
grey/black discharge. In severe or neglected
cases the infection can spread to involve the
underlying corium. The degeneration of the horn
is due to infection with bacteria and especially
fungi. Wet unhealthy stable conditions, poor
routine foot care, prolonged confinement,
overgrown ragged frogs and long or high heels
which produce deep sulci. Most of these
conditions can be corrected by a blacksmith.
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Nail Prick occurs at shoeing when a nail
penetrates the live structures of the foot. It
happens most commonly if the horse is restless or
fractious, the hoof wall is particularly thin or
broken, the shoe is too small or the hoof has
been dumped. Dumping means Dumping is excessive
rasping of the outside of the walll usually at
the toe, but it can extend all the way around the
wall. Nail Bind occurs when the nail of the shoe
is driven close to, but not into the sensitive
structures of the foot resulting in pressure and
inflamation.
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TendonitisIt is inflammation
of the superficial deep digital flexor tendons
(DDFT) often referred to as a bowed tendon due to
the bowed appearance of the tendons on the back
of the cannon bone. The strap that crosses the
cannon bone in front is the extender ligament
Tendonitis of the DDFT is fairly rare.The damage
can range from mild tearing of tendon fibers to
actual rupture of the entire tendon and the
bone-attached ligaments. Tears in tendons are
best diagnosed by ultrasound. Tendonitis is
predominately a forelimb problem.
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The 2 primary causes of superficial DDFT are
either acute trauma due to overload, or a
cumulative damage due to repeated damage to the
tendons. Aside from poor conditioning and
misapplied racing bandages, high racing speed can
bow a horse.Hyperextension of the distal
interphalangeal joint as a result of allowing the
toe to grow and thus rise may cause chronic or
acute tearing of the DDF tendon fibers.
Normally, tendons are elastic so that they can
stretch with routine overloading. This is
referred to as elastic deformation.
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Clinical signs of superficial DDFT include
heat, tendon swelling (edema) and thickening and
lameness. X-ray images of lame horses likely are
less effective than ultrasound. Inflammation may
be best demonstrated by IR photographs. Note
that in many late cases of inflammation,
antiinflammatary drugs are contraindicated, as
inflammation speeds up the healing process.After
tendon fibers are torn, hemorrhage results in
blood clots likely along with swelling and
inflammation. As the inflammation and the blood
clots subside, scar tissue forms in the place of
the displaced fibers.
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Typical bowed tendon. This horse might be checked
for bone chips with X rays.
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A low bow in the left leg
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LaminitisLaminitisinflammati
on of the laminas of the foot--is a common,
painful and sometimes disastrous condition of the
horse hoof that has always been known. Laminitis
occurs when the coffin bone (distal phalanx) and
the inner aspect of the hoof wall are separated.
Nevertheless, a blacksmith can likely cure a
given problem with well managed racehorses.
Laminitis isessentiallya problem of neglected
horses.
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Bring the hoof and the coffin bone back into
their original positions through trimming.
Optimize blood flow through the foot by a little
walking or roping. Removing the cause of
laminitis overload of the coffin bone.
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There are 2 kinds of laminas. Dermal laminae grow
outwards from the laminar dermis attached to the
coffin bone. They are made of living connective
tissues that fold into primary finger-like
structures each of these in turn is folded into
hundreds of feather-like secondary laminas. These
dermal laminas interdigitate with corresponding
epidermal laminae, each again of primary and
secondary generations, that project inward from
the inner horny surface of the wall, anchoring
the coffin bone to the hoof wall. The amount of
folding in the laminas increases the surface area
of bonding.
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The blood supply to the equine foot is unusual.
All arteries have receptors in their walls that
can bind specific chemical messengers circulating
throughout the body. The binding of these
chemicals some like bradykinin causes the
dilation or constriction of the arteries changing
the amount of blood reaching the tissues. Blood
rich in the oxygen and nutrients necessary to
sustain living tissues is carried in arteries
from the heart to the hoof. It then passes
through a capillary bed in the dermis where
oxygen and nutrients can diffuse to the cells.
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Acute laminitis occurs anywhere from 24 to 72
hours after the initial damage to the basement
membrane and is heralded by the clinical signs of
pain. Signs of acute laminitis include1/ severe
lameness, reluctance to move or even to
recumbency 2/ typical stance to try to get
weight off the toes front feet out in front if
only the forelimbs are involved all 4 legs in
under the body if all limbs are involved
pointing with a leg if only one limb is involved
3/ increased digital pulses are almost always
present 4/ continued heat in the foot
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Disposing Factors in LaminitisNumerous
predisposing factors have been identified. They
can be divided into 6 major groups1/ High
heels2/ Carbohydrate overload excess grain,
lush pasture, sudden feed change 3/ Endotoxemia,
sepsis, shock colic, intestinal obstruction,
pleuritis, retained placenta, metritis, abortion
4/ Excessive unilateral weight bearing
post-fracture repair, severe lameness 5/
management unconditioned animals worked on a
hard surface, cold water ingestion by overheated
horse, overweight animal
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TherapyThe treatment of
horses that develop acute laminitis can be
considered an emergency. A delay of even a few
hours can make the difference between a
successful outcome and a failure. If any of the
known risk factors for laminitis have occurred,
therapy should be started before the clinical
signs become visible. The treatment should be
focused on restoring the circulation of the hoof
and of course the reattachment of the laminas to
the coffin bone. It is at least 8 weeks before
prognosis. In chronic cases, 4 months to a year
are required before future performance abilities
can be estimated.
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Navicular diseaseFinding excessive
fluid in the navicular bone, especially diffuse
fluid in the medullary cavity, indicates
navicular disease.The diagnosis is considerably
refined for about 10 years via the use of
magnetic resonance for soft tissues. Ultrasound
produces poor images in boney tissue. X ray is
often used. Again, the basic cause is not at all
always overwork pulling on bones, ligaments and
muscles, although the basic treatment is always
rest. The main cause is high heels and sometimes
bar shoes.
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A low bow with navicular disease
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What have we learnt ?We should know 2
facts about lameness 1/ racing on turf rather
than dirt will vastly reduce injuries, and 2/
velocity over pulse gives the horses capability
at a given moment.Running on grass will GREATLY
reduce owner costs, but raise racetrack
costs.Training horses as a single set not as
individuals is the universal rule. As very many
are quite beyond their capacities, lameness is
the common result and has the common factor of
uneconomic rest.