Clean Run - November 2017 - 59

breeders) had no reason to believe
that ETOs might be caused by something other than physical pain or training. No one even considered that the
cause(s) of ETOs could have a heritable
component. Thus, there was no reason
to be concerned about it when selecting breeding stock. But now that we
understand more about ETOs, those
who are breeding performance dogs
that will be required to jump should
be concerned.
Today, most breeds in agility are still
bred for a purpose other than agility,
which creates a problem if that other
purpose does not involve jumping. It
becomes very difficult to determine
which sire and dam will produce nice
agility prospects! Even in breeds that
excel in agility, performance dog
breeders are the minority or they
do not focus solely on agility. Many
breeds are bred primarily for conformation or companionship, with only a

Emmetropia
Myopia
Hyperopia
Not Tested

small percentage bred strictly for performance. Many pups that enter agility
are offspring of dogs that have never
jumped a jump in their lives. Some
breeds participate in more than one
performance sport. A breeder that focuses on producing top herding dogs
is understandably not going to be concerned about jumping ability.
Many breeders are still unaware that
a problem even exists. For those who
are not breeding performance dogs
and selling them as agility prospects,
it probably doesn't matter. But it is
very important that performance dog
breeders understand what ETOs are
and the impact they might have on the
future of their puppies. These breeders need to educate themselves and
evaluate their dogs. Most breeders are
unaware of the risk factors for ETOs
and that they are presumed to be inherited, or they are aware and do not
want to admit it. The unusually high

incidence of ETOs in some lines (and
some breeds) very strongly supports
the heritability of ETO causes, and the
current recommendation is that breeders (and puppy buyers) err on the side
of caution.
The current thinking is that breeding
an affected individual is inadvisable. It
is also not advisable to breed an unaffected individual that has produced
affected pups in one or more litters,
particularly when bred to a different
individual each time, or an unaffected
individual that has siblings, or other
close relatives with ETOs. Obviously,
much more data needs to be collected
to ascertain which breeds have higher
incidence of one or more of the risk
factors. In one study, conducted to
determine whether the distribution of
naturally occurring myopia in Labrador
Retrievers has a genetic component,
the results indicated that indeed there
was a signiﬁcant genetic component.3

From: A Canine Model of Inherited Myopia: Familial Aggregation of Refractive Error in Labrador Retrievers.
Invest. Ophthalmol. Vis. Sci.. 2008;49(11):4784-4789. doi:10.1167/iovs.08-1828

This diagram shows the relationships between the 134 dogs in the study, including the mating loops. The sample included
62 females and 72 males, with 92 dogs having yellow, 37 black, and 5 unknown coat color. Although the diagram shows dogs from
37 litters, it does not show all dogs in each litter. Refractive error was obtained from an average of 42% of dogs from each litter
(only those whose refractive errors were determined are shown).
November 17 | Clean Run

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Table of Contents for the Digital Edition of Clean Run - November 2017
