(Fwd) Equine Foot Physiology

["Judith Lessard" <lessardj@cvm.msu.edu>]

The following information is from the College of Veterinary Medicine 
at Michigan State University.

Judith Lessard
Editorial Assistant
Publications and Media Relations
College of Veterinary Medicine
Michigan State University
<lessardj@cvm.msu.edu>


October 15, 1998

Contact:	Robert Bowker, VMD, PhD	
  (517) 353-4532

  or

  Linda Chadderdon
  Information Officer
  (517) 355-5165	

A New Theory About Equine Foot Physiology

A Michigan State University College of Veterinary Medicine
researcher has pieced together a new picture of equine foot
physiology that suggests vascular systems in horse hooves function in
much the same way that air- or gel-filled running shoes do.

"Moving liquids are the best way to dissipate energy," said Robert
Bowker, a professor in the College of Veterinary Medicine's Anatomy
Department. "That is why some of the major running shoe
manufacturers market products that contain liquids in their soles."

 Bowker has theorized a "hemodynamic flow" process in which he
 proposes that much of the blood in horse feet fulfills purposes other
 than providing nutrients to hoof tissues.

"It dissipates energy within feet that is created during the act of
galloping, trotting or walking," he said. 

This theory not only proposes a new physiology for horse feet, it
also suggests some of the more widely held views in the equine
industry should be revised or, at least, re-examined. 

For example, Bowker's theory presents a wholly different view of how
horse feet respond to ground impact.

It also suggests horses with navicular disease may not need to be put
down and that hoof trimming techniques might need to be reviewed.

"We may need to be trimming hooves so that more of the back part of
the foot-including the frog--bears the initial ground impact forces
and weight," Bowker said.

 This would encourage development of tissues that dissipate more
 energy when hooves hit the ground. "If hooves are trimmed so that the
 frog rests on the ground," Bowker said, "it stimulates the back part
 of the hoof to grow more fibrous and cartilaginous material."

With digital cushions constructed of more resilient tissues, less
ground impact energy would be transmitted to foot bones and
ligaments, reducing internal foot problems, such as navicular
disease.

Currently, equine foot physiology researchers subscribe to one of
two anatomical theories: pressure theory or depression theory. Both
seem to be mirror images of each other.

"Pressure theory says that when the hoof hits the ground, the
pressure of the impact hits the frog of the hoof, which causes the
back part of the foot to move outward," Bowker said.

Depression theory suggests that when impact on the ground occurs, the
pastern descends and depresses the digital cushion inside the hoof.

"According to both theories, these actions push hoof cartilage to the
outside, with the digital cushion absorbing the energy," he said. 

Both theories state that blood is pumped from the hoof at impact.

Yet both theories share a single problem. Researchers who attempt to
duplicate depression or pressure theory in the lab or on live horses
are unable to do so. 

Problems arise when researchers attempt to account for how the energy
of the hoof's impact with the ground is dissipated.

"The digital cushion is made of soft, elastic tissue and acts like a
spring," said Bowker.  "So for every action, we would expect a
reaction of equal force." 

Yet when researchers put energy measurement devices into digital
cushions, that does not happen.

"When the hoof is in the air, it registers zero pressure," he said.
"But  when it hits the ground, instead of registering positive
pressure, it is actually negative."

Bowker's hemodynamic flow hypothesis suggests this negative pressure
is actually created by the outward movement of the hoof cartilage.
This movement creates a vacuum action that sucks blood from beneath
the coffin bone into the rear portion of the hoof.

"As the blood moves to the rear of the hoof through microvessels in
the lateral hoof cartilage, it dissipates the energy caused by its
impact on the ground, much like fluid-filled running shoes do," he
said. 

In developing this new theory, Bowker observed that horses with good
feet have more blood vessels in the lateral cartilage of their hooves
than those that had histories of foot problems. 

Additionally, blood vessels in healthier animals were located inside
the lateral cartilage of the hoof, and the digital cushion on these
animals tended to be made of cartilagineous material instead of
elastic tissue. 

This is particularly true for horses in breeds that are said to have
good feet, such as Arabians. "It was also true for Quarter Horses in
their mid-20s with no history of foot problems," he said. 

Bowker believes environmental factors also contribute to the
formation of these kinds of tissues.

"We found more cartilagineous digital cushions consistently,
regardless of breed, in domestic horses from the Rocky Mountains,
where harder ground surfaces and higher altitudes may contribute to
their formation," he said. 

In regions of the country where ground surfaces are softer, more
horses have digital cushions made of elastic tissue.  "We believe
these horses have a greater chance of having internal foot problems."

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