Australian Shepherd Health & Genetics Institute

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White Fright

Double Merle Puppies
Double Merle Puppies

by C.A. Sharp

France-flagRev. April 2013


The subject of white, or mostly white, Aussies is a contentious one wherever Aussie people congregate.  Too much white is “bad” and people who keep such Aussies are branded as ignorant or irresponsible.  As a retired breeder, an authority on Aussie genetics and (gasp!) the former owner of a homozygous merle bitch, now deceased after a long and happy life, I suppose I ought to address the issue.

Before you start lighting your kindling, I do not recommend or promote the keeping of white Aussies by most people under most circumstances.  The bitch I had was intentionally kept up and donated for non-invasive research purposes.  When my bitch Moby’s scientific “career” was over, I kept her because she loved life and I loved her.

Predominantly white Aussies are almost always the result of merle-to-merle breeding.  These homozygous (meaning “two like genes”) merles have inherited the merle color gene from both parents.  They are usually, but not always, blind and/or deaf.  The defects are variable, so the amount of vision and hearing loss will range from little to total—with most tending toward the bad end of that scale.  The eye defects result from improper development of the tissues of the eye while the loss of hearing is attributable to a lack of pigment in the inner ear.

I have heard people say repeatedly that homozygous merles also suffer other kinds of defects, but I have found no hard evidence of this in the veterinary literature.  It has not been the case with the homozygous merle Aussies of which I have personal knowledge.  I don’t know if the lack of these other defects is because we keep so few of these dogs or because they do not happen.

If you breed a homozygous merle, whatever the breed, you should only do so with a non-merle mate.   And unless you have considerable experience in that breed, I strongly discourage you from doing it at all.  If you breed a homozygous merle, all of its offspring will probably be merle.

I say probably, because sometimes something called “germinal reversion” occurs and a homozygous merle will produce a non-merle pup.  This has been reported in the scientific literature in Aussies (Sponnenberg, J Hered, 1984) and there are anecdotal reports of it happening in Shelties and Collies.  These non-merle pups are not cryptic merles.  They have no merle spots on them and if bred to other non-merles, all their pups are non-merle.

Homozygous merle Aussies are usually, but not always, predominantly white.  This is why the standards discriminate against white coloration beyond an “irish” pattern (blaze, collar, chest, underbody and legs) and why people are discouraged from keeping white pups.  But it is possible to have a “normally” marked merle Aussie that is also homozygous.

Betty Nelson, the chair of ASCA’s original Genetics Committee for the length of its existence, had a homozygous merle bitch who was a medium blue shade with a stripe down her nose, a white throat and chest, one white foreleg and white toes.  Hardly “full white trim.”  But for her line (Woods—one known for almost no white) this was a lot.  She was also light in color compared to the normal deep pigmentation of her line.

The situation is similar in breeds which also have merle and do not have white markings.  I once asked a Dachshund breeder about “dapples,” which is what they call merles. He told me that the homozygous merles in some lines had a lot of white but in others they had very little.  This ties in with what I know of Aussie lines with little white.

There are also predominantly white Aussies which are not homozygous merles at all.  Their white arises from genes that give many breeds of dog white markings.  These genes can cause everything from no white, like a Dachshund, to almost all white, like some Fox Terriers.  Aussies with “too much white” that were not homozygous merles were once far more common than they are today.  I can remember seeing several when I first started in the breed in the early 70s.  Look at the historical section of ASCA’s first yearbook for pictures of some of them.

White Aussies are rare today because we have been slowly eliminating the “more white” forms of the white marking genes from our gene pool by not breeding Aussies with more than allowable white (though the preference for white trim on the show dogs does have some pushing the envelope.)

If you don’t want to produce homozygous merles in your litters, it’s easy to avoid doing so:  Don’t breed two merles together.  That’s the route I took when I was breeding. If you do plan merle-to-merle breedings you must decide beforehand what you will to do with the homozygous pups.

If you want to keep a homozygous merle, you must be willing to devote yourself to keeping it safe from dangers it cannot hear or see for its entire lifetime.  These dogs are not for everybody.  While my Moby was one of the sweetest Aussies I’ve ever owned, I’ve known of others whose temperaments were terrible.  Bad temperament is not directly a result of the dog being a homozygous merle, but if a dog is genetically predisposed to temperament faults the sensory deprivation and ease of startling them with things they cannot hear or see may push borderline dogs over the edge and make those who would have been bad even worse.  Proper socialization is necessary for any Aussie, but doubly so for a homozygous merle.

If you do keep a white Aussie, you should be doing everything you can to educate people who see the dog and might think it is pretty about the problems of homozygous merles.  The rescue organizations have enough trouble placing sound dogs; they don’t need more pound puppies who were dumped because ignorant buyers discovered after the fact that the pretty white Aussie they chose had a problem.  Or because they decided their noble intention to “save” a blind, deaf pup had become too much bother.

If you produce a homozygous merle, you have a responsibility to see that it is taken care of.  If you acquired it, you have made a commitment for the life of that dog to caring for a handicapped animal.  If you want to breed it my first advice is don’t, but if you do you damn well better know what you are doing.