Basset breeders don’t think the
breed has. This is an opportunity
for the Basset Hound community
to nip POAG in the bud before it
becomes prevalent in the breed.
Don't we wish we were in that 
position instead of trying to slowly
reduce the number of carriers in
the PBGV population? So spread
the word to your Basset friends.

Genetic Consequences of

Breed Formation. Dr. Bell gave
two presentations. The first was on
breed development and maintenance. Dr. Bell described
how individual species developed through natural selection
to improve the chance for survival and the ability to 
reproduce. Individual dog breeds were developed through
artificial selection for specific traits. In a typical breed, only
a small percentage of the population reproduces. This is not
necessarily detrimental to the breed if the selectionincreases
the breed’s superiority. As breeds were selected and 
studbooks closed, there was a significant reduction in 
diversity. Typically, breeds go through population expansion
followed by purging of lines that show deleterious traits. 
Dr. Bell stressed the importance of allowing breeds to grow
with distinct lines. In general, population contraction causes
a loss of breed diversity and fewer quality breed lines.

The dark side of breed development is the appearance of

diseases and disorders. Reproduction will always lead to some
deleterious mutations which can increase in frequency with
either natural or artificial selection. Also, a disease can increase
in frequency in a particular breed due to founder effect. As
defined by Wikipedia, founder effect is the loss of genetic
variation that occurs when a new population is established
by a very small number of individuals from a larger population.
Inbreeding can lead to homozygosity of recessive mutations
(inheriting the mutation from both parents) with resulting
decreased litter size, increased neonatal death, shortened life
span and specific genetic diseases. Dr. Bell noted that all breed
databases show abandoned lines. The popular-sire syndrome
is the single most influential factor in restricting breed gene-
pool diversity because it leads to the loss of other quality
male lines. Healthy breeds need outbred clusters and different
line-bred families to create selective pressure for the breed.

Roles, Risk, and Responsibilities: A blueprint for 

Genetic Health Improvement.Dr. Bell’s second presentation
focused on the responsibility of breeders to improve the
health of a breed. He stressed that genetic disease is often
predictable and preventable. However, veterinarians report
that less than 5 percent of their clients’ puppies come from
health-tested parents. Breed characteristics are easy to 
maintain whereas genetic health is not, and requires 
constant selection. Prospective breeding dogs should 
have complete health exams, including musculoskeletal,
ophthalmologic, cardiac and metabolic tests. In addition,
medical history of close relatives should be examined.

Dr. Bell was adamant that a breeder’s health guarantee for

a puppy is not a replacement for health testing of the sire
and dam. Breeders should plan matings that minimize 
the risk of producing individuals with genetic diseases. 
Conscientious breeders understand that adverse test results
limit breeding options. The problem lies with breeders who
hide the occurrence of genetic disease. If test results are not
available for prospective mates, assume that they are 

affected or carriers. Conscientious
breeders provide documentation.

Breed clubs share responsibility

for the health of the breed. Clubs
should conduct regular breed
health surveys, provide pre-
breeding health screening 
recommendations, support 
reporting of test results in an open
health registry and periodically 
review breed standards. Breed clubs
should advocate against extreme
phenotypes and educate judges to

select for moderation. Finally, clubs should fund research
into breed-related genetic diseases.

Veterinarians should be knowledgeable about disorders in

various breeds, know screening tests and assist breeders with
genetic counseling. They must discuss pre-breeding tests
with clients and promote open reporting of health results.
Pet owners should be counseled to only get pets from 
breeders who perform health tests.

DNA Tests: How to Choose Which Ones to Use. Dr.

Mellersh closed the conference with a discussion of how to
choose DNA tests to be recommended by a breed club. Here
is a list for breeders and clubs to consider. I have included
some PBGV-specific information with each point.

Is the DNA test based on good science?Research that led to

the DNA test should be published in a peer-reviewed journal.
Dr. Mellersh’s identification of the POAG mutation in
PBGVs has been submitted to a peer-reviewed journal.

Is the mutation associated with the disease in your breed?

Most tests assay for mutations found in a specific breed or a
small number of breeds. If the test is specific for Beagles, it
won’t be helpful for PBGVs. There is a PBGV-specific test for
POAG available through AHT.

Is information available regarding the risk of developing the

disease?If the risk of developing the disease is low, select
carefully against the mutation. If the mutation is common,
then rigorous selection against the mutation may do harm.
Unfortunately, the POAG mutation is more common in PBs
than expected. Almost half of tested dogs carry the mutation.
It is important to proceed slowly to eliminate the disease.

Do you know mode of inheritance?To use the DNA test 

results for planning matings, one must know whether the
mutation is recessive or dominant, autosomal or sex-linked.
POAG in PBGVs has an autosomal recessive inheritance.

Is there information on the prevalence of the mutation in your

breed?This will help monitor progress towards eliminating
the mutation from the breed. Tested samples are not typically
representative of the breed. It is important to determine
prevalence in a representative cross-section of dogs, which
requires the assistance of breed clubs. So far, we only have
data from tested samples. The PBGVCA is planning to do a
cross-sectional prevalence survey, partnering with Dr. Mellersh.

What will you do with the results? A breeder’s priority

should be to reduce the frequency of the mutation over time
while protecting the genetic diversity of the breed. Dr. Bell
will discuss this point in detail in his health seminar at the
2016 PBGVCA National Specialty.

Which testing laboratory would you choose? The testing 

lab should have a good reputation and International 
Organization for Standardization accreditation. Best is if the
testing lab is affiliated with the research lab that identified
the mutation, which is the case with Dr. Mellersh.  

I

Saber Tails   

IWinter 2015    

www.pbgv.org

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The eye clinic at the 2016 national specialty

is the perfect opportunity to have your

PBGV’s baby browns examined by a board-
certified veterinary ophthalmologist. Please

sign up for the eye clinic when you register

for the conference. Eye exam, tonometry and

gonioscopy will be available.