Q: "I have sent you a copy of the e-mail i sent [NAME OMITTED], bcause
[NAME OMITTED], told me that hip dysplasia is not a problem in America...
i du not agree that ferrets don't have the weight/muscle/bone growth
imbalance like large dogs.  Do you agree with [NAME OMITTED]?  Hip
dysplasia is a problem in ferrets in Denmark, but they do not show any
pain what so ever, and i think that is why the problem does not exist in
America, because no x-rays have been taken."
 
A: First, I am not a veterinarian; I am a zooarchaeologist intensively
trained in comparative osteology (among other things).  Most of the vets
on this list know far more about hip dysplasia than I do.  I hope they
will speak up and correct any mistakes I might make in this response.
 
Hip dysplasia (HD) is a progressive, degenerative joint condition found
in large breeds of dogs, although it is not unheard of in smaller canines
and other animals.  The Hip Dysplasia Registry of the Orthopedic
Foundation for Animals (OFA) at the University of Missouri, Columbia sets
standards for hip dysplasia in dogs, and reviews and grades hip dysplasia
in canines and other animals.  Researchers at the University of
Pennsylvania (PennHip) are also looking at the condition, as well as
numerous veterinarians and animal scientists.  Hip dysplasia has been
noted in Maine Coon cats, but is not limited to that variety.  Dysplasia
has been reported in pigs, sheep, other domestic animals, and even in
humans.  According to Dr. Greg Keller of the OFA, hip dysplasia has NOT
been reported in ferrets (at least to the OFA), and he does not know of
any peer-reviewed literature that suggests the condition has ever been
reported.  My own extensive and protracted search has found none.
 
I am not going to discuss the causes of hip dysplasia; how could I explain
in a few paragraphs a disease that in 1996 one of the top researchers, Dr.
James A. Baker, called "baffling?"  Thought to be heritable, caused by
multiple genes at multiple locations (polygenic), hip dysplasia is not
limited to hips, but can effect all joints, especially those of the
shoulder, knee and between the vertebrae.  Regardless of the obvious
genetic influence, there is a strong environmental aspect controlling
gene expression--hip dysplasia can be controlled or prevented by reducing
growth during development by limiting food intake.
 
From my point of view (as a zooarchaeologist), it is extremely difficult
to identify pathological cause in prepared skeletons.  Veterinarians
have the advantage in that they can inspect X-rays taken from living
individuals, and physically inspect affected individuals for pain,
mobility, range of motion, and other symptoms.  All I can do is note the
presence of osteoarthritis on individual bones and realize some sort of
degenerative changes have taken place, but without usually being able to
say WHAT caused the problem.  That is to say, I can easily note the
presence of arthritic changes, but I usually can't say what caused them.
However, in cases of animals having hip dysplasia, I CAN identify the
cause in maybe 70% of the cases (based on blind tests), based on a number
of criteria: no obvious presence of injury or infection, presence of
osteoarthritis in shoulder, knee, and intervertebral joints, and specific
changes to the femoral-acetabular structures.  I have found these changes
in the skeletons of large dogs, a few smaller ones, sheep, and a few cats,
but as of yet, I have never seen them in a ferret, and I have inspected
hundreds of ferret skeletons.
 
That is not to say I haven't found arthritic changes in ferret hips; they
are common enough in older ferrets for me to consider their presence as a
typical condition.  However, in the example of dysplasia I have inspected,
the walls and floor of the acetabulum are eroded, and the neck and head
of the femur are significantly changed.  The only time I have seen those
changes in ferret skeletons have been because of injury or infection; not
because of a heritable condition.
 
I have a few thoughts on the issue.  While dysplasia is found in most
breeds of dogs, it tends to affect the larger breeds most often.  The same
is true with dysplasia in cats.  These animals have been selectively bred
to be significantly larger than their progenitors (gray wolf and wildcat).
Ferrets have, to date, been spared the human desire to manipulate size.
Second, ferrets, as with other small mustelids, have "loose joints"; that
is, ferret limbs are designed to twist and turn in ways impossible for
cats or dogs (or at least quite painful).  This is because ferrets evolved
chasing animals down burrows and follows other adaptations allowing
hunting in small, narrow spaces, such as a unified internal carotid, small
external ears, powerful neck, and extremely supple vertebral column.
Because of this, there are subtle differences in how the femur is attached
in the hip when compared to dogs or cats.  For example, the acetabulum
is shallower, which allows the femur greater range of motion; this
"looseness" allows the legs great flexibility when wiggling down burrows.
The neck of the femur is also comparatively longer in ferrets, aiding
extension of motion.  These differences MAY preclude the types of problems
seen in the joints of large cats and dogs.  Third, the problems found in
cats and dogs can be largely eliminated by slowing growth by limiting diet
in developing individuals.  Ferret size is ALREADY limited by diet and
neutering, so the rapid growth that imbalances the weight/muscle/bone
ratios in dogs and other domesticated animals is not typically seen in
ferrets.  Therefore, I strongly agree with your original respondent that
hip dysplasia is not a problem in American ferrets.
 
As for the lack of observation of dysplasia in American ferrets being due
to a lack of X-rays: I disagree.  X-raying ferrets is common in veterinary
care because it is a relatively rapid and cheap method to check for
obstructions, masses, organ enlargement, and bone problems.  While vets
may not be primarily looking for signs of hip dysplasia, they WOULD notice
the changes in the joints associated with the disease.  Maybe not every
vet, but enough would notice so that a warning would be mentioned in
ferret health literature.  Remember, osteoarthritis is PAINFUL; even
without significant osteological changes, animals suffering from hip
dysplasia are in obvious pain from movement or physical manipulation.  If,
as you mention, ferrets are not in pain, it is doubtful they are actually
suffering from dysplasia.  I wonder if the laxness in the ferret hip
joint--normal compared to dogs or cats--is confusing the issue.
 
Personally, while I think ferrets COULD potentially suffer from dysplasia
of the hip (or other joints), they just haven't been subjected to the same
type of selective breeding for size as in cats or dogs (or other domestic
animals).  From an outsider's perspective, it seems that breeding for size
triggers the problem.  However, as an owner of EXTREMELY large ferrets, I
worry about the current trend of some ferret owners trying to breed
ferrets much larger than typically found.  It may be that if the trend
continues, ferrets will suffer dysplasia as genetic defects are increased
with inbreeding for size.
 
However, I have some good news.  If ANYONE on this list (or reading this
post) suspects a ferret has hip dysplasia, I can offer some unoffical
help.  Unofficially, for a limited time, if you forward the x-rays (or a
good copy) to me, then a "volunteer" experienced with rating joints for
dysplasia will inspect them to see if dysplasia actually exists.  This is
in effect a free consultation by someone highly experienced and trained
in the subject.  Obviously, I am trying to protect the identity of the
person making this offer so they are not inundated with phone calls or
mail by ferret owners by-passing their personal vet, trying to get a free
consultation.  So inundate me--I will forward all serious inquires,
x-rays, and contact information to the proper person(s).
 
Bob C
 
Illustration of the hips can be found in back messages by using the
search engine at http://groups.yahoo.com/group/Ferret-Health-list .
[Posted in FML issue 3644]