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PUTTING THE CARTILAGE BEFORE THE HORSE
by Cathy L. Smith
With horses, being able to move is everything.
A horse will do everything in its power to keep on its feet,
because without motion it knows it will fall prey to any predator
that comes around. And most horse owners want to see their
animals able to perform, whether it is for trail riding or
as a multi-million dollar racehorse. Not only that, but we’d
like to know they are not in pain when doing so.
To that end, Dr. Jamie MacLeod has been continuing
his studies of diseases and conditions of the equine bones,
joints, and musculature at the Maxwell H. Gluck Equine Research
Center. One of the center’s newest researchers, MacLeod
holds the John S. and Elizabeth A. Knight Chair in Musculoskeletal
Science. He comes to the Gluck Center from Cornell University
where he expanded on his burgeoning interest in equine movement
and, more specifically, the effects of work and movement on
joint cartilage (also called articular cartilage).
Ideally, articular cartilage is smooth and
unblemished. It is the most abundant type of cartilage found
in the body and lines the bones in the joints, as well as
providing cushioning for weight bearing on the bones. It allows
the bones to slide over each other with minimal resistance.
It’s no surprise that movement causes wear and tear
to the cartilage. But this natural process can become a problem
when the wear is extreme or there is injury to the cartilage.
Most of the time when this happens, arthritis sets in.
“Lameness is the main reason that the
athletic careers of horses are limited,” MacLeod said.
“It’s a huge problem.”
For reasons that are not well understood,
MacLeod said, cartilage does not heal well. In contrast, bones
usually heal without difficulty. And the mystery is that many
mammals bones start out as cartilage when they are in the
fetal stage. Most of the cartilage forms into bone as the
fetus develops.
He said the more a horse is used and the more
strenuous his activity, the more wear and tear there is on
the cartilage. So if a horse is put to work at an early age,
it follows that it will have more wear on its cartilage than
a horse that begins working later in life. And, MacLeod added,
the type of work the horse does will determine which joints
will be most affected.
“A race horse injury will be different
than what is seen in a show jumper or a draft animal. Horses
often accumulate joint injuries throughout their lives—just
like people do. If you ask a premier race horse to be athletic
early in its life, it will accumulate injuries or at least
aches and pains earlier in life,” he said.
What MacLeod is focusing his research efforts
on is the study of gene expression in chondrocytes. Gene expression
refers to the sequence of a gene’s DNA which alters
to become the structures and functions of a cell. Chondrocytes
are the cells that synthesize and maintain the cartilage throughout
life. He feels gene expression promises a better solution
to healing cartilage than surgery. In the same vein, he is
looking to new information supplied by the Equine Genome Project
(see Horse Cures of the Future: A Map Would Help) and microarrays
(the study of microscopic DNA spots to measure gene expression).
He said these two research strategies will provide he and
other equine researchers with more powerful solutions to assist
them in their experiments.
With a better understanding of chondrocyte
cell biology, MacLeod hopes to answer the questions of what
can be done to prevent cartilage damage and, should such damage
occur, what can be done to help the cartilage to heal. Both
answers mean a lot in the equine world—and to the field
human medicine as well--since the disease process of arthritis
caused either by sudden trauma or life’s normal wear
on joint cartilage is very similar in horses and people.
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