From:
Bob C
Date: 2001-12-21 06:22:00 UTC
Subject: Bob C: Hip Dysplasia in Ferrets? (Text)
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