The
following was written for Elm Hill Labradors by PennHIP
(University of Pennsylvania Hip Improvement Program) for
additional information please log on to www.pennhip.org.
The
documentation reflects Elm Hill Labradors desire to only breed
quality Labradors that support a "Hip Improvement Program". We
stand by the University of Pennsylvania Hip Improvement Program in
all respects with a genuine desire to improve the breed standard.
PennHIP 101 and introduction to canine hip
dysplasia
Since the 1960’s veterinarians and breeders have
attempted to eliminate canine hip dysplasia (CHD) from our canine
population by selectively breeding only dogs without sign of the
disease on hip radiographs. Although a marked reduction in the
disease has been achieved this way, to this day CHD remains to be
one of the most common orthopedic diseases in dogs leading to
painful, debilitating arthritis.
For this reason, Dr. Smith and his colleagues at
the University of Pennsylvania investigated other ways of diagnosing
hip dysplasia and in the late 1980’s founded the University of
Pennsylvania Hip Improvement Program (PennHIP). PennHIP differs from
the conventional diagnostic method used by the OFA, BVA or FCI, in
that instead of examining only one x-ray, PennHIP requires three.
The way the animal's legs are positioned for the conventional (OFA)
view often masks looseness of the hip so that the hip joints appear
to be tighter than they really are. The positioning for the three
PennHIP x-rays is therefore crucial and veterinarians have to be
specifically trained in the technique.
The three views for the PennHIP evaluation are
the 1. hip-extended view, 2. compression view and 3. distraction
view. The first view is the same used by conventional hip scoring
methods, this x-ray is evaluated for signs of arthritis which is the
hallmark sign of hip dysplasia. The second and third views are used
to measure the looseness (laxity) of the hip joint. Ever since the
1960’s it has been empirically accepted that joint laxity leads to
arthritis and therefore the diagnosis of canine hip dysplasia is
based on the radiographic signs of arthritis and/or laxity.
From the PennHIP distraction x-ray a true
measurement of joint laxity is possible, it is a purely objective
quantification, it is repeatable and highly accurate. This
measurement is called the distraction index (DI) and is a number
between 0 and 1. The distraction index quantifies the "looseness"
(laxity) of a dog's hips, the closer to 0 the tighter; the closer to
1 the looser. Looser hips have a higher risk for developing
arthritis. The studies show that dogs with a DI below 0.30 are
virtually at no risk for developing arthritis and can be considered
"truly dysplasia free". Interestingly, dogs from breeds known to be
dysplasia-free, such as performance Greyhounds and Borzois, all have
DIs below 0.30. As the DI increases above 0.30 the probability of
developing arthritis increases so that dogs with a DI of 0.70 have
almost a 100% likelihood of developing OA.
Scientific investigations have shown that joint
laxity (looseness) is inherited from one generation to the next. By
accurately identifying dogs without joint laxity it is possible to
selectively breed tight hipped dogs and thus eliminate the disease
from the canine population.
So ideally, to make the most rapid improvement
in hips, it might be recommended to breed only dogs with DIs below
0.30. Unfortunately most of the popular breeds of dogs have only a
few breed members in this range. For this reason, to avoid the
potential adverse effects from inbreeding, PennHIP calculates a
ranking of one dog's DI to the DIs of all the other dogs within the
same breed. The breed average DI (actually the breed “median”) will
be represented by the 50th percentile. Dogs in the 60th
to 90th percentile have DIs well above the breed average
and those in the 10th to 40th percentile have
DIs well below the average. PennHIP recommends breeding ONLY
above-average dogs to improve the overall breed average. Basically
when you breed only above-average dogs within a specific generation
or breed interval, the breed average will move toward 0.30 from one
generation to the next. By applying even greater selection pressure
e.g. breeding only dogs that are in the 70th or 80th
percentile, more rapid genetic improvement will be made.
For clarification, if a dog has a DI in the 80th
percentile it means that he has better (tighter) hips than 80% of
the dogs within the breed but worse (looser) hips than 20%.
As genetic progress is being made the breed
average will change. This means that a Labrador Retriever at the 60th
percentile born in 2012 will likely have a tighter DI than a Lab in
the 60th percentile born in 2008, but the total number of
“breedable” dogs within a generation or breeding interval will
always be 40% of the population. I think you will agree that 40% of
your breed is a substantial number of dogs from which to select
breeding candidates such that you maintain the other important
characteristics of the breed standard. Currently the average (50th
percentile) DI for Labrador Retrievers is 0.46, and the DI for dogs
in the 60th percentile is 0.43. PennHIP therefore
recommends breeding only dogs with DIs of 0.43 and better (tighter).
Breeding average hipped dogs (so for Labs 0.46) is not recommended
since it will not help to improve the gene pool and only create more
average hipped puppies.
A few PennHIP facts:
- PennHIP can be done as early as 16 weeks of age
with great accuracy.
Screening puppies
will provide valuable information to breeders and owners in
regards to the dog’s
susceptibility for developing arthritis and value as breeding
stock.
- PennHIP provides valuable information regarding
your dog’s risk for developing arthritis.
Knowing your dog’s risk will allow
you to take preventive measures early before
the disease
progresses. Weight management, controlled exercise and dietary
supplements have
been shown to prevent or delay the onset of arthritis.
- PennHIP offers breed specific ranking of your
dog
Understanding the rank of your dog
compared to the rest of the breed will enable
you to make the best
decisions when considering to breed.
-PennHIP is an objective measurement that is
repeatable and highly accurate.
Methods such as the OFA, BVA and FCI
rely on subjective scores where two
evaluators often do
not agree with one another.
- The positioning of the dog’s legs during the
PennHIP procedure allows for an accurate measurement of joint
laxity.
Joint laxity is the primary risk
factor for the development of arthritis. The degree
of laxity is
correlated to the dog’s risk for developing arthritis.
- During the PennHIP procedure dogs must be
sedated or anesthetized.
Dogs need to be completely relaxed
when the PennHIP x-rays are taken, sedation
is necessary so as
to eliminate the natural reflexes and muscle contraction.
- PennHIP does NOT hurt your dog’s hips, the
joints cannot be falsely made to look looser or tighter than they
really are.
The hip joint is a ball on a rope,
meaning that no matter how hard you pull, you
can only pull as far
as the rope allows.
- The heat cycle does NOT affect PennHIP
readings.
The only hormone that has been shown
to affect laxity reading is called relaxin.
This hormone is
produced just before and during the birthing process. Relaxin is
closely related to
the hormone responsible for lactation, therefore it is recommended
to not do PennHIP until 6 to 8 weeks after weaning the puppies.
- PennHIP has a mandatory submission policy
This means that all x-rays taken for
PennHIP must be submitted to our Analysis
Center, this allows
us to have the ONLY non-biased database currently available.
