Still some misconceptions about genetics (no pun intended--well, maybe a
little...) and whether Marshall Farms does or doesn't engage in disreputable
methods in breeding its ferrets.  First, I agree with Lisa that MF does need
to be a responsible breeder.  If MF keeps its ferrets poorly housed or
mistreats them, that is another matter entirely.  If USDA has issued
warnings or criticized them for poor care, then ferrets owners deserve to
know whether MF has corrected those problems.  Although if they have had
problems in the past and corrected them, MF certainly doesn't deserve to
wear a scarlet letter forever, either.
 
Regarding the genetic health of their ferrets, I still do not believe
sufficient evidence has been presented to clearly show that MF's breeding
practices have led to a number of alleged health problem in their ferrets
compared with other breeders.
 
LisaFerret commented that:
 
>Inbreeding predisposes an animal to certain defects and susceptibilities to
>some types of cancer.  For instance, the recessive genes are more likely to
>become "dominant" when interbreeding occurs - some of the nicer recessives
>are blue eyes in humans - but can be as bad as Crohn's disease or breast
>cancer.
 
I suspect that you meant to say that "recessive genes are more likely to
*breed true* when interbreeding occurs." If so, that's completely correct.
Interbreeding can increase the prevalence of recessives in a population, and
you picked a pretty good example with Crohn disease.  (Geneticists have
decided they don't like possessives and so all of the ___'s have been
dropped from disease names.  Don't ask me why.  It looks weird.)
 
Crohn disease is now known to be an inherited defect in some families
descendent of Ashkenazi Jews from Poland and Russia.  (For the curious, this
particular gene is on the short arm of human chromosome 16 in the p12-q13
region, although it is not the only gene believed to increase the risk for
the disease.)  It is probably a good example of a defect showing up in
increased numbers due to a combination of factors related to a too-closed
gene pool.  Some Jewish and other religious groups have in the past
restricted intermarriage with those outside their group or kicked out people
who did marry outsiders.  The rate of recessive genetic diseases increases
(1) if the group isn't diverse enough to begin with, (2) if those who have
children with genetic diseases don't refrain from having children, or (3) if
someone with the defect (or a carrier) has *lots* of children who live long
enough to pass it on to many, many others--a so-called "founder's effect."
(Yes, THAT's where Queen Victoria comes in.)  In humans, this has been
studied extensively in island populations which also have a lot of
inbreeding--perhaps not with siblings or first cousins, but eventually, most
people end up marrying a relative.
 
MF *could* be guilty of enriching their gene pool with undesirable recessive
genes in this way, but so could *any* other breeder who breeds for a
specific trait.  In fact, there are those who breed ferrets with Waardenburg
syndrome for certain coat patterns even though these ferrets will be deaf
and/or blind or have other health patterns.  I haven't heard of any
Waardenburg ferrets coming from MF.  Whoever is breeding those ferrets, I
think it is reprehensible to purposely breed for coat color that is linked
with such severe defects.
 
>Marshall Farms themselves advertised last winter about their genetics.  The
>ad read, "The secret is out - MARSHALL FARMS! bred to be genetically pure."
>In my opinion, that means genetically alike.
 
Whoa.  Think about that one for a minute.  That's the advertising people at
MF talking, not the breeders.  People who advertise scientific products and
services typically know only enough science to scrape by and often play fast
and loose with terminology to sell their "product," whether it's a flask or
a ferret.  As a scientist, "Bred to be genetically pure," means nothing to
me.  It's non-specific.  Are the animals congenic?  Are they bred to exclude
known disease genes?  Do they lack retroviruses?  I couldn't tell you.  I
can tell you that whoever wrote that ad didn't know much about genetics.
 
I do agree with Kirstin Hendrickson in that if Marshall Farms were indeed
breeding genetically identical animals, they would be carbon-copies of each
other in almost every respect, and it's obvious that MF ferrets vary in
size, shape, color, temperament, etc.  BTW, true congenic animals are so
similar that organs can often be transplanted between them without the need
for anti- rejection drugs.  The vets can correct me if I'm wrong, but I
don't think that is possible with MF ferrets.  (The fact that there appears
to be only one blood type in ferrets [unlike humans] does *not* mean they're
genetically identical.)
 
Lisa responded to my comments about non-MF ferrets with early-onset cancers
by saying...
 
>As far as the one year old ferret is concerned, even in perfect conditions,
>aberrations occur - that's why some MF ferrets are healthy and do not
>develop any major problems...
 
That's not a very convincing argument *if* you're saying that any example
that refutes your position is an aberration.  That's reminiscent of
statisticians who disregard "outliers" because they don't fit the model used
to predict risks or associations.  Usually outliers (e.g., people who have
really high cholesterol but never get heart disease) tell you that (1) the
real association is more complex than your model can handle, or that (2)
your model will predict what's happening for most people, but you'll always
be way off for a small percentage.  In the case of MF, I don't think there's
enough systematically collected information to tell what the real situation
is.
 
--Jeff Johnston ([log in to unmask])
[Posted in FML issue 1696]