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Although Labs are generally healthy, as a breed they are susceptible to
a few genetic health problems: hip and elbow
dysplasia, Progressive
Retinal Atrophy, dwarfism, centroneuclear
myopathy (CNM), exercise induced collapse (EIC), megaesophagus, and hypothyroidism. Hip Dysplasia
Canine hip dysplasia (CHD) results from poor development of the hip
joint and affects dogs of many different breeds. It is inherited,
but because of the polygenic ("multiple genes") mode of
inheritance it has proven to be difficult to eradicate. For example, it
is possible for two dogs with "good" hips to produce a puppy
with CHD. Additionally, environmental
factors, such as trauma or excessive growth, can contribute to the
problem.
The severity of CHD can vary from mild with no symptoms to severe and
crippling arthritis. The first signs generally appear before a dog's
first birthday and may only appear as a slight irregularity in gait.
Young, affected dogs can improve somewhat as they mature and develop a
stronger musculature, but even these dogs will develop arthritis later
in life.
Diagnosis can be made by x-ray as early as 4 or 5 months of age, although
at this age there is a small chance of error. All dogs intended for breeding should
be x-rayed once they have matured, but before being bred for the first
time. Twenty-four months of age is considered the minimum age for an
accurate determination and for certification by the Orthopedic
Foundation for Animals (OFA). Bitches should not be x-rayed within
about four weeks before or after her heat cycle because the additional
hormones circulating in her system at this time may cause a false
positive reading.
X-rays sent to the OFA will be examined by three veterinary
radiologists who will determine whether or not the dog is dysplastic and
will also assign a rating. Non-dysplastic hips will receive a rating of
Excellent, Good, or Fair. Dysplastic hips will receive a rating of Mild,
Moderate, or Severe. There is also a Borderline rating and the OFA will
usually request an additional x-ray be taken about 6 months later.
Arthritic changes over this time period will help determine whether the
dog is actually dysplastic.
Between January 1974 and December 2001 there were 134,979 Labs
evaluated by the OFA. Of these dogs, 16.1 percent were graded Excellent,
while 13 percent were graded as dysplastic. Although the Lab is ranked
as the most popular breed in the United States, it was ranked 67th in
the number of dysplastic dogs. Breeders are slowly making headway toward
eradicating this problem. Before 1980 only 10.4 percent were rated as
excellent, but for dogs born in 1994/95 16.6 percent were rated
excellent for an increase of 59.6 percent. During the same time period
dysplastic dogs declined from 14.5 percent to 11.7 percent for a
decrease of 19.3 percent.
Breeding only unaffected dogs probably accounts for the majority of
the improvement. The OFA believes that environmental factors and high
caloric intake do not cause CHD and that high doses of vitamin C won't
reduce or prevent CHD. However it is wise to do everything possible to
prevent CHD, therefore we recommend the following: Only breed unaffected
dogs and only buy puppies from unaffected parents. Line the whelping box
with carpeting or towels instead of newspapers to provide better
traction. Prevent excessive jumping (e.g. into the back of a pickup) or
forced exercise (e.g. roadwork) until the dog is mature (at least 24
months). Keep dogs on the lean side, instead of obese. Provide a good
quality diet.
Can high doses of vitamin C help a dysplastic dog? Read an article
by Larry Mueller, Editor of Hunting Dogs, for his experiences.
Elbow Dysplasia
Elbow dysplasia (ED) is a general term for various inherited
abnormalities of the elbow. These abnormalities are: fragmented coronoid
process of the ulna (FCP), osteochondrosis dessicans (OCD), and ununited
anconeal process (UAP). They can occur separately or in any combination.
Both elbows are affected in about 20 to 35 percent of affected dogs.
Males are more commonly affected, possibly because of their larger size
and faster growth.
A dog with ED will typically show foreleg lameness between
five to 12 months of age, but some dogs may not appear lame until much
later in life. Some dogs may have obvious pain, while other affected
dogs have an abnormal gait. The lameness or abnormal gait may be
sporadic. Additionally the problem may appear worse after increased
exercise, jumping or sharp turns.
In addition to lameness, other signs of elbow dysplasia include front
legs that are rotated inward with the elbows sticking out and a decrease
in the range of motion. Less commonly seen are muscle atrophy and joint
capsule thickening.
Most cases of elbow dysplasia can be confirmed with x-rays. Multiple
views are taken, and generally both elbows should be checked. However
some cases
of FCP may be difficult to diagnose using x-rays because of the
relatively small size of the coronoid process. In these cases a CT scan
may be useful.
Treatment consists of surgery for some animals, in addition to pain
medication. Unfortunately only about half of the dogs that are treated
medically and/or surgically will have a satisfactory long-term recovery
because arthritic changes will continue throughout the dog's life. Early
treatment seems to be the most successful. Another option can be to feed
nutraceuticals, such as chondrotin and/or glucosamine. These may take a
considerable amount of time before any benefits are noted. Swimming can
help build muscles to improve joint stability without undue strain on
the joint. Weight reduction may also help reduce strain. For young dogs,
modifying food intake to keep the growth rate at a minimum may be
helpful.
Although scientists are studying the causes of elbow dysplasia,
results have been varied. Like hip dysplasia, it is believed to be polygenic ("multiple genes"),
but environmental factors can also contribute. Some of these factors may
include excess weight, consuming excess protein or calcium, rapid growth
rate, excessive exercise, and trauma.
The OFA also has an elbow registry and will certify elbows anytime
after the dog is two years of age. They also give preliminary evaluations, and
considering that elbow dysplasia often develops before 12 months of age
a preliminary evaluation may be prudent. Between January 1974 and December 2001, there were 16,831 Labs
evaluated for elbow dysplasia. Of these, 87.4 percent were rated normal
and 12.6 percent were rated dysplastic.
Progressive Retinal Atrophy (PRA) and other eye problems
Labs are also at risk for several eye problems including: PRA, cataracts, and retinal dysplasia.
PRA is a progressive deterioration of the light-receptive area (retina) of the eye, and
will result in blindness.
Symptoms are subtle, often starting with night blindness and eye
dilation. Typically the age of onset is between four to six years which
makes it difficult to identify carriers and remove them from the
breeding pool.
This disease is caused by a simple recessive gene. For
the dog to be affected he must have two copies of this recessive gene. A
dog that has only one copy of the gene is a carrier and will show no
clinical symptoms, but can pass the recessive gene on to his
descendants.
A genetic test is available for the prcd form of PRA (the only form
found in Labradors) through Optigen.
Your vet would need to draw a blood sample from your dog and submit it
for the DNA test.
Cataracts are relatively common in dogs. Most are hereditary, however
haziness or cloudiness in the eyes of an older dog is often not caused
by cataracts. Some cataracts are stable while others may progress in
severity. Surgery can often help dogs with severely impaired vision.
Retinal dysplasia (RD) or "folds" is inherited with
dwarfism. In mild cases, sight is only slightly affected. In severe
cases the dog may be blind and have skeletal abnormalities. Because RD
may disappear with age, it is important to have puppies checked by a
board-certified ophthalmologist, preferable
between eight to ten weeks of age. At this time, folds are more easily
detected. As the puppy grows the folds may straighten out and become
almost impossible to diagnose. Dogs with any type of RD should not be
bred because they probably also carry the gene for dwarfism.
Additionally one of that
dog's parents is also probably a carrier for dwarfism.
All breeding stock should be examined annually by a board certified veterinary
ophthalmologist who has the special equipment and training needed to properly examine the dog's eyes.
This exam is painless. The results can then be submitted to Canine
Eye Registration Foundation (CERF).
Dwarfism
In Labradors, dwarfism has been linked with retinal dysplasia or
"folds." These problems seem to be more common in dogs with
American field trial breeding.
A dog that received two copies of the gene for retinal dysplasia will probably go blind and will develop abnormally. Generally the legs
will bow outward, giving a bulldog-type appearance with short legs and a
disproportionately large head. Any dog with these symptoms should never
be bred. Additionally the dog's parents and most, if not all, of his
siblings, should not be bred because they are carriers of the gene even
though they may not show any outward signs of it.
Another form of dwarfism may be caused by an abnormality of the
pituitary gland. The pituitary gland secretes a growth hormone, and if
this hormone is decreased or absent the dog will not develop properly.
Unlike chondrodystrophic (skeletal) dwarfs, these dogs remain
proportionate, just smaller than average. Generally an owner will notice
the dog failing to grow around eight to twelve weeks of age. Other signs
might include: a soft, wooly coat, hyperpigmentation (darkening) of the
skin, gradual alopecia (hair loss), and little, if any, sexual
development. These animals may be helped with injections of growth
hormones over several months, thyroid supplementation and/or cortisone
replacement. Check with your vet for the best treatment of your dog. In
addition, all dogs with this condition should be neutered.
Centroneuclear Myopathy
This condition was known by several names, including muscle myopathy,
muscular dystrophy, myotonia, generalized muscle weakness, and
polyneuropathy. Dogs are the only mammal with a similar condition in
people known as centroneuclear myopathy. Because research on the dog
form can help research on the people form, the dog form has also been
named centronuclear myopathy.
First diagnosed in 1976, this condition is characterized
by a marked deficiency of skeletal muscle mass, abnormal posture, and a
stiff hopping gait.
The first signs of this condition may be a significant weight loss as
early as two weeks, followed by a lack of tendon reflexes. Between two and
five months of age, the puppy may show an awkward gait and a reluctance to play as
much as their littermates and may tire more easily. More
advanced symptoms include pronounced muscle wasting (particularly in the
head, shoulders and hips), a short, stilted stride and "bunny
hopping" with their rear legs, an arched back and low head posture,
and a lanky appearance.
Watch a movie of an affected dog at http://labradorcnm.com/pages/site/Clinics_movie.html#
This condition is inherited as an autosomal recessive gene, meaning
both parents carry the gene even if they don't show any symptoms. All
offspring of an affected dog will carry at least one copy of the gene.
A genetic test is available through the CNM
Project at the Alfort School of Veterinary Medicine in France.
There is no treatment, except for rest. Some dogs may respond to
Diazepam or steroids. Dogs with muscle myopathy may make an acceptable
house pet with a normal life span, however they are very sensitive to
stress and cold.
Exercise Induced Collapse (EIC)
Labrador, Chesapeake Bay and Curly Coated Retrievers can be affected by
a genetic problem causing collapse. Affected dogs are often described as
extremely fit and muscular. Although they can tolerate mild to moderate
exercise, strenuous exercise combined with extreme excitement can induce
weakness followed by collapse.
Signs start with a rocking or forced gait, followed by weakness in
the rear legs. Some dogs continue to run while dragging their rear legs.
Some dogs also exhibit weakness in their front legs. Some dogs lose
their balance and fall over. Most dogs remain conscious.
It is important to stop all exercise at the first sign of in
coordination or wobbliness. A few dogs have died during exercise or
while resting just after the episode.
In Labs, this condition is genetic and inherited as a recessive gene.
A dog with one copy of the gene (a carrier) would not show any symptoms,
however he can pass the gene to his offspring. A carrier should only be
bred to a dog clear of this gene to avoid producing an affected dog. An
affected dog can also be bred, but should only be bred to a clear dog to
avoid producing an affected dog. All puppies of an affected dog will
carry the gene.
A genetic test is available from the Veterinary
Diagnostic Laboratory at the University of Minnesota.
Megaesophagus
Megaesophagus is so-named because of the enlargement of the esophagus
caused by the loss of peristaltic function. (Peristalsis is the process
of muscular contractions that move food through the esophagus.) Dogs
with megaesophagus will usually regurgitate their food soon after
eating. It is often seen in young puppies, but may develop later in
life. Other signs include labored breathing (possibly aspiration
pneumonia), fever, lethargy, and nasal discharge. Some dogs may outgrow
this condition, while there is no improvement in other dogs.
To confirm the diagnosis, your veterinarian may decide to take chest
x-rays, run blood tests, and run a urinalysis. Although there is no
specific treatment for megaesophagus, your veterinarian may be able to
identify an underlying cause and provide supportive care. Feeding small,
frequent, high-caloric meals from an elevated stand may also help.
In Labs, the condition appears to be genetic, however the mode of
inheritance is still unknown. In some breeds it is caused by a recessive
gene and in other breeds it is caused by a dominant gene. Until more is
known about this condition, it is safest to avoid breeding any affected
dogs, their parents and their siblings.
Hypothyroidism
Hypothyroidism occurs when the thyroid gland does not secrete enough of
the thyroid hormone called thyroxine (T4). T4 plays a major role in
controlling metabolism and is necessary for growth. The other main
thyroid hormone is called triiodothyronine (T3). Both T3 and T4
circulate through the bloodstream and are regulated by the thyroid
stimulating hormone (TSH).
The most common cause of
hypothyroidism is autoimmune thyroiditis. This occurs when the body
makes antibodies against the thyroid gland which gradually destroys the
gland and decreases its ability to secrete T4.
Because T4 affects many internal organs a deficiency can manifest
with varied symptoms. Some possible symptoms include obesity, lethargy,
mental dullness, hair loss, hyperpigmentation (darkening of the skin),
mood swings, facial paralysis, and disorientation. Other possible
symptoms include diarrhea, constipation, vomiting, abnormal heat cycles,
lowered body temperature and even heart problems. One study found that
the majority of dogs with hypothyroidism had some kind of skin
abnormality, however some dogs may not have any symptoms.
The disease can occur at any age, but tends to affect dogs starting
at two to five years of age. Dogs may appear normal for years, only to become hypothyroid at a later date.
Some of the tests to determine hypothyroidism include a blood test, a
skin biopsy, TSH test, or a thyroid biopsy. The blood test is most
commonly used, however other factors may also cause a decrease in the
production of T4. These factors include using medications such as
cortisone, valium, and anticonvulsants, and diseases such as
Cushing's disease, diabetes, chronic renal failure and liver disease. A
skin biopsy, by itself, probably wouldn't be conclusive evidence of
hypothyroidism. The TSH test was considered quite reliable, but it can
be expensive and difficult to find TSH. The thyroid biopsy is rarely
used because is so invasive. Sometimes the only way to determine
hypothyroidism is to administer the treatment for several months and
note the results.
Treatment consists of correcting any underlying problems and,
perhaps, administering a synthetic thyroid hormone. Generally a change
in attitude and energy level is seen very quickly, however skin changes
and hair regrowth may take several months. Dogs usually remain on this
hormone for life, but the hormone level should be checked every six to
12 months to adjust the dosage amount.
Because there appears to be a genetic predisposition to
hypothyroidism, breeding stock should be tested annually starting at
sexual maturity. After about four years of age the dog can be tested
every other year.
Of the 119 test results submitted to the OFA for Labradors between
1974 and 2002, 79 percent tested normal.
If you're thinking about buying a Lab puppy, be sure to check with
the breeder about the possibilities of these problems in their puppies.
At the very least you should insist that both parents have hip and eye
clearances.
Updated: September 2009
The information given here is to help you learn
more about your dog and not to replace your veterinarian's advice.
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