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> I had an unfortunate incident over Christmas - lost a lovely little
> filly at six days old - no apparent cause.  A friend suggested I test
> the stallion for SCID and will do so before doing any more breeding to
> him.  I've been reading up on it and getting lots of facts, but my
> question is this : what are your feelings concerning the defect?  How do
> you go about deciding to breed a carrier, if you do have one?  What are
> the general feelings in the breeding community about a well-known
> stallion or mare that are carriers?  Is the stigma still alive and well?
>  If your stallion proves positive, do you geld or do you just make an
> informed decision about future breeding?
First of all, if the filly died of "no apparent cause" odds are it was not
a SCID death.  Foals who die of SCID generally die of some sort of
infectious disease--pneumonia, scours, something--and they simply don't
respond to treatment, since they don't have a functional immune system.

That said, being a SCID carrier is simply one fault to be weighed among
all the other faults that any given horse has.  Given that there is a test
for the carrier status, if one even just tests one's breeding stallions,
and then if one comes up with a carrier stallion, then tests the mares to
whom he is to be bred to make sure he is not bred to any carrier mares,
then there is no need to EVER produce a SCID foal.  The carrier status
does not affect the horse in any way.

We see so many horses being bred with long backs, long cannons, shallow
heart girths, lack of angulation in the hindquarters, etc., ad nauseum,
that breeding a GOOD stallion that is a carrier, and breeding him wisely,
makes sense.  All else being equal, it makes sense to use the
non-carrier--but in my experience, all else is frequently not equal.

Is there still a stigma?  Yes.  If you are standing a stallion to the
public, you will run into prejudice.  However, here at least, I do believe
the prejudice has been at least somewhat replaced with an educated
approach to how to use carriers wisely.  If you do have a carrier, you
have to ask yourself what your own breeding goals are--if your main aim is
public stud, it may make economic sense to geld.  If you have a specific
breeding program, then it is often well worth using carriers that possess
traits that you wish to perpetuate--we have one adult carrier stallion
that fits that role, and I do sincerely hope that we get a non-carrier son
from him.  That said, though--we currently have one son (just a baby and
not yet tested) and if we get another son, unless the colts are of similar
quality, the SCID carrier status would not be the deciding thing in
choosing which one to carry on.  The stallion is old, and so even if I
have to use a carrier son to replace him, I can still breed the SCID gene
out in a subsequent generation.

We are not yet to the point of having our entire herd tested, although we
have most of our stallions done--but my goal over time is to test stepwise
so that we can identify any further potential carriers in our herd, and
know which foals we need to test to track the gene.

One of the best people to talk to on this subject is geneticist Michael
Bowling, in Davis, CA.  He does a better job than I do of explaining how
abrupt cessation of the breeding of all carriers does irreparable harm to
the gene pool, whereas gradually lowering the carrier rate over time by
testing and judicious use of carriers while gradually selecting for
non-carrier descendants over several generations is much healthier for the
breed.

Heidi



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