AND BREEDING PRACTICES IN THE LABRADOR RETRIEVER
Jack Vanderwyk, January
Many veterinary specialists
are able to tell us what genetic defects are and how we can prevent them,
namely not breeding with affected animals. That sounds very simple, but
it isn’t. As for the Labrador Retriever, we are talking about 111 (one
hundred eleven) genetic defects, of which only a few are tested: several
eye diseases like PRA and cataract, elbow dysplasia and hip dysplasia.
If an animal is tested and no signs of genetic defects are found, a breeder
may be quite sure that the offspring of this animal will not develop these
genetic defects, especially when these genetic defects weren’t found in
the parents of this animal either. However, if an animal is tested and
signs of genetic defects are found, while this animal was born out of phenotypically
unaffected parents, the breeder has a problem. Should he use this combination
again, or should he stop breeding one or both parents, even when all the
other puppies are phenotypically unaffected?
Nobody is perfect
No human being, no
Labrador Retriever is perfect. We may check for 4, 6 or 10 out of 111 genetic
defects and a dog might prove to be phenotypically unaffected, but this
can mean that the dog is a carrier of dozens of other genetic defects.
Several decades ago the Germans thought they were the perfect race and
they even invented “scientific” methods to keep it that way, but we all
know that the perfect human being does not exist. With all the genetic
and medical knowledge we have, science didn’t succeed in creating a human
being without any genetic defects, let alone a Labrador Retriever. All
the programs invented to eliminate a genetic defect like canine hip dysplasia
didn’t lead to the fact that we are now able to guarantee the production
of Labrador Retrievers without hip dysplasia, or will be in the near future.
So there are other
facts to consider.
Manifest and hidden
Some genotypical defects
will never become phenotypical genetic defects, and some genetic defects
will only become phenotypical in some animals, maybe even once in every
20 or 30 generations. Other genetic defects will only become phenotypical
as a result of wrong exercise or wrong nutrition, especially during the
first year of a puppy’s life. In his article “Are Hip Dysplasia and Elbow
Dysplasia Hereditary Diseases” (July 2002) Professor Doctor H.A.W. Hazewinkel
from the Department of Clinical Sciences of Companion Animals of the Utrecht
University in The Netherlands emphasised the important environmental influences
on the occurrence of hip dysplasia and elbow dysplasia in Labrador Retrievers.
Thus it is possible that generations and generations of Labradors will
be produced who are phenotypically free of hip dysplasia and elbow dysplasia,
and will satisfy many, many buyers of Labrador Retrievers for their entire
life, while other Labradors, from the same parents, but raised under less
optimal environmental circumstances, will develop hip dysplasia or elbow
dysplasia. So if you want to be sure if your puppy has no genetic defect
like hip dysplasia or elbow dysplasia, you could provoke these genetic
defects by overfeeding and physically overstressing it during the first
year of its life.
However, most people
realise that they didn’t buy a test automobile but a living animal and
will not take the chance that a skeletal defect develops. They realise
that “responsible ownership” includes taking good care of your puppy and
preventing it from developing skeletal defects.
Further more: breeders
may claim that “incompetent use” of a puppy leads to the fact that they
are no longer responsible for the quality of their “product”.
Mode of inheritance
and degree of heritability
Our Jennifer (born
in 2001) has all the looks of a Flatcoat Retriever, but her mother was
never near a Flatcoat Retriever and none of her ancestors, siblings or
offspring look like a Flatcoat Retriever. Still a lot of them must carry
the gene for the Flatcoat phenotype. Going back in time I discovered an
ancestor who was a Flatcoat-Labrador interbred, born in 1921. All these
years Labradors were produced who didn’t look like Flatcoat Retrievers,
until our Jennifer was born 80 years later. It might take another 80 years
before this trait will show up again in Jennifer’s offspring, but it might
never happen again.
Some genetic traits
have a high degree of heritability, while other genetic traits or defects,
like hip dysplasia and elbow dysplasia, have a low degree of heritability.
No serious breeder will breed a dog with phenotypical hip dysplasia or
elbow dysplasia, unless he knows for sure that such a defect was caused
by the wrong nutrition or wrong physical exercise (trauma) during the first
year, that the parents and grandparents of this dog didn’t have the phenotypical
defect, and that this dog is unique and important to the development of
his breeding stock (or even to the breed as a whole).
There are four major
modes of inheritance that cause most of the defects in dogs: autosomal
recessive, autosomal dominant, sex-linked recessive and polygenic.
PRA and brindle, for
instance, are autosomal recessive traits.
1. Both parents are
proven carriers, but generally show no phenotypic manifestation of the
2. The trait tends
to occur in one generation and then skips one or two generations until
carrier descendants are again mated, allowing the genes to be expressed.
3. Males and females
are affected equally.
4. Matings between
carriers (heterozygotes) on the average produce 25% affected (homozygous
recessive), 50% carriers (heterozygous) and 25% that do not have the mutant
gene (homozygous dominant).
Some forms of epilepsy
and deafness are autosomal dominant.
1. At least one parent
of an affected offspring must show the trait.
2. The trait occurs
in successive generations (no skipping).
3. Males and females
are affected equally.
4. About 50% of the
offspring of an affected parent will be affected.
(Hemophilia A, for
instance, is a sex-linked recessive defect.)
1. On the average
half the male offspring of a carrier dam are affected.
2. On the average
half the female offspring of a carrier dam are carriers.
3. The trait may skip
4. The pattern of
transmission is often called oblique, because the gene goes from phenotypically
normal dams, to affected sons, and then to phenotypically normal carrier
5. Affected males
transmit the gene to all of their daughters and to none of their sons,
because the sons receive the Y- and not the X-chromosome.
6. If both parents
are affected with the trait, all offspring are affected.
7. For an affected
female offspring to emerge, the dam must be at least a carrier, and the
sire must be affected with the trait.
8. Most affected offspring
in a typical pedigree are male.
9. There may be related
affected males on the maternal side of the pedigree, but only rarely (if
ever) on the paternal side.
10. All male offspring
of an affected female are affected with the trait when the sire is normal,
and all daughters are phenotypically normal carriers.
These traits are more
complex than the typical dominant or recessive genetic trait. The additive
interaction of the genes can cause variable results and the gene can be
easily passed on to other generations without being identified.
Canine hip dysplasia
and elbow dysplasia are believed to be polygenic defects.
1. As with the recessive
trait, both the sire and the dam must contribute one or more of the genes
that cause the abnormal phenotype in the offspring.
2. Unlike recessive
traits, the contribution from the sire and dam need not to be equal.
3. Since we do not
know the number or the specific effect of the genes involved in polygenic
traits in dogs, no predictable Mendelian ratios are associated with these
4. Both sexes are
affected with polygenic traits (excluding sex-limited traits), but not
necessarily in equal numbers.
5. The trait may skip
generations and may appear to be erratic in occurrence.
Especially when it
comes to polygenic defects it is hard to tell which one of the parents
is mainly responsible for the defect in part of the offspring. It is throughout
possible that the bitch and the sire are equally responsible, but it could
be that the bitch’s part is 99,5% and the sire’s part is 0,5%, or the other
way around. A breeder might exclude both animals from the breeding stock,
but this could mean that he would exclude a valuable animal that would
produce normal puppies if mated to another partner.
DNA: the final solution?
“Studies in dogs with HD have shown that HD may be a polygenetic (sic!)
disease, needing more abnormal genes to act together in expressing HD in
the affected dog.” In other words: he’s not sure. Science knows too little
about genetic defects to be able to tell us breeders which dogs will produce
offspring with genetic defects, and which will not. Hazewinkel also wrote,
“DNA-screening tests have to be the future goal for the international kennel
clubs and breeders associations”.
Okay, so it is possible
that one day a simple DNA screening test will tell us if a Labrador Retriever
is affected by one or more out of 111 genetic
defects. But will it tell us something about the severity of these
genetic defects? Let’s presume that all Labrador Retrievers carry the genes
for hip dysplasia and elbow dysplasia. All of them. Let’s presume that
all Labrador Retrievers have been doing so since the 1850’s. This would
mean that these genetic defects can’t be eliminated. So what should we
do then? Stop breeding Labradors and let the breed become extinct? Or rely
once more on the mode of inheritance and degree of heritability, like we
have been doing for more than 150 years? 150 years in which breeders of
Labrador Retrievers provided millions of people with a lifetime friend,
a unique dog, healthy on the outside but carrier of a gene that might pop
up once in a while? Maybe even once in 80 years?
Maybe we should just
wait until there is a matured and reliable DNA test that is able to tell
the breeder or buyer of a puppy what their chances are to get a phenotypically
healthy puppy, even if it might carry the gene for a defect hidden deep
down somewhere. And one thing is certain: no DNA test will ever be able
to provide us with perfect Labradors, let alone perfect human beings. Because
they do not exist and they never will.
Throwing out the
baby with the bathwater
Most Labradors are
screened for hip dysplasia and elbow dysplasia between the age of one and
two years. The results of these screenings are usually final, if the owner
reconciles to the facts. To illustrate how “scientific” the screening results
are: it is possible that an x-ray produces the result of HD-C (moderate
bad hips) and that the same x-ray, examined by the same expert a few weeks
later (probably in a better mood or with more time) produces the result
of HD-A (OFA excellent). Another disturbing fact is that most veterinary
specialists who examine x-rays without seeing the dog, are not (yet) able
to tell the difference between dysplasia caused by genetic defects or dysplasia
caused by trauma.
So for a breeder it
is rather difficult to trust the experts’ judgement.
Dr. George A. Padgett,
DVM, advises us to “look at the whole dog”. When you see a completely healthy
dog with all the traits you want to see in a Labrador Retriever, that is
your starting point, because that is the phenotypical dog you want to reproduce.
And as long as scientists aren’t able to tell us if this super dog produces
0.001 or 99.999% of the genetic defects, breeders have to rely on what
the eye can see.
A simple example of
“throwing out the baby with the bathwater” is our Oliver. When he was one
year old Oliver’s eyes, hips and elbows were screened. He had perfect hips,
perfect elbows, and perfect eyes. The next year his eyes were screened
again. A very small triangle was found in both eyes. The diagnosis was
posterior polar cataract, a type of cataract due to a dominant gene, appearing
as an inverted Y or triangle, or irregular circle of opacity, at the pole,
and not associated with the hyaloid artery. These cataracts show little
tendency to progress until senile changes occur, and in Oliver's case I
was assured by two veterinary eye specialists that he will never have any
seeing problems, nor his offspring, as long as he is not bred to a bitch
with that same innocent form of cataract.
In March 2003 Oliver
visited another veterinary eye specialist, a professor this time, for a
second opinion. This veterinary specialist also assured me that dogs affected
with the posterior subcapsular triangular cataract rarely if ever become
blind, and in Oliver's case he was very sure that Oliver will never have
any seeing problems.
In 2004 Oliver was
screened once more. At first the veterinary eye specialist came to the
conclusion that Oliver has perfect eyes, but when she read that Oliver
was screened before and the little triangle was found, she took another
look and had to admit that there is a little defect, not the kind of cataract
that will ever cause any seeing problems, but a very minor defect.
You should meet Oliver.
He is a great dog, a beautiful dog, a lovely dog, and people are standing
in line to buy his puppies. Looking at the whole dog, as Dr. Padgett advises
us to do, and at the same time looking at the very minor genetic defect
that will never cause him or his offspring any problems, I simply had to
come to the conclusion that it would be a very stupid thing to exclude
this super boy from my breeding program.
is a generic term, like “virus”. AIDS is caused by a virus and a
simple cold is caused by a virus. However, it would be a very bad thing
to put both illnesses in the same category. No one would ever get another
The same applies to
other genetic traits. Sure, if it’s clear that my dog will transmit a serious
genetic defect to his offspring, I will exclude that dog from the breeding
program immediately. But what if the chance that this will happen with
my dog is 0.001%? What if the chance that this will happen with all dogs
is 0.001? Should I move on to breeding worms?
If veterinary scientists
want us to take them seriously, they should provide us with realistic and
feasible prognostications. And in the cases they are not able to do so
(yet), they should restrain from screaming blue murder or coming out with
Genetics and the
legal and moral liability of the breeder
A breeder is not liable
for any genetic defect when he:
1. Has done all he
can to research the ancestors of his breeding stock, to make sure that
these dogs didn’t have any serious genetic defects.
2. Had the parents
of his puppies screened for serious genetic defects in the breed.
3. Has made sure that
any signs of serious phenotypical defects in his breeding stock could only
have been caused by environmental influences.
A purchase deed regarding
to a puppy is usually not a contract in which the rights and the observance
of duties of the buying side and the selling side are of equal standing.
Observance of the seller’s duties can be verified thoroughly, by health
certificates, pedigree certificates, etc., but the only verifiable duty
of the buyer is payment. The buyer might say that he gave his puppy the
right nutrition, the right amount of food, the right physical exercise,
etc. but the seller is not able to verify the observance of these important
Due to the fact that
the right nutrition and the right exercise of a Labrador puppy during its
first year can be of overriding importance regarding to the question if
the puppy will develop a manifest genetic defect or not, in other words:
to the fact that a phenotypically normal puppy may change into a phenotypically
abnormal puppy, it is not advisable to include genetic matters in the purchase
deed. A breeder may guarantee the fact that a puppy is a pure-bred Labrador,
descending from this sire and that dam. He may guarantee the fact that
both the sire and the dam were phenotypically normal and healthy at the
time of the mating and that the puppy was phenotypically normal and healthy
at the time of deliverance. But no breeder can guarantee that a phenotypically
normal Labrador puppy will not change into a phenotypically abnormal Labrador
puppy, and no breeder can guarantee that the puppy will become a show champion,
because all these matters are beyond his range of influence. Pure research
showed the important environmental influences on the occurrence of genetic
defects during the first year of a puppy’s life. If a buyer of a puppy
is not willing to take this risk, he should buy an adult Labrador and not