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"Lethal White"

The Merriam-Webster OnLine Dictionary gives the following definition of the word lethal:

Main Entry: 1le·thal
Pronunciation: 'lE-th&l
Function: adjective
Etymology: Latin letalis, lethalis, from letum death
Date: 1604
1 a :of, relating to, or causing death <death by lethal injection> b:capable of causing death < lethal chemicals>
2:gravely damaging or destructive :DEVASTATING <a lethal attack on his reputation>
synonym see DEADLY
-le·thal·i·ty /lE-'tha-l&-tE /noun
-le·thal·ly /'lE-th&-lE /adverb

It also states:

Main Entry: 2lethal
Function: noun
Date: 1917
1:an abnormality of genetic origin causing the death of the organism possessing it

And then goes on further to define a lethal gene as:

Main Entry: lethal gene
Function: noun
Date: 1939
:a gene that in some (as homozygous) conditions may prevent development or cause the death of an organism or its germ cells -- called also lethal factor, lethal mutant, lethal mutation

Where did this term originate?

The original breeders of Australian Shepherds were ranch people, and had horses as well as dogs. There is an actual lethal gene found in certain types of Paint horses that results in a white foal with blue eyes. These foals are unable to digest their food and die of colic within a few hours to days after birth. It is impossible for them to survive. Because of a superficial physical resemblance (and approximately the same birth odds - 25%), the name was used to describe the mostly white pups of merle parents.

Why is this term inaccurate?

  • The puppies do not die shortly after birth, like the Lethal White foals do. While they may have vision and hearing problems (or may not), they are otherwise healthy and capable of growing and developing normally.
  • They are rarely pure white (as the foals are). While carrying more white than is the "norm" for their lines, they usually have markings of some sort, and can have brown eyes (unlike the foals). See our Double Merle pictures page for a sample of the pattern variety found in these dogs. You may also want to look at the pattern white pictures for comparison.

So what is the correct term?

The genetically correct term for these dogs is "homozygous merle," which simply means the dog carries 2 copies of the merle gene. We've also heard these dogs referred to as "fatal whites," "merle merles," "white merles," "merle whites," "excess whites," "over merled," and "rare whites" (they aren't rare). "Double Merle" (abbreviated "MM"G) is a more accurate as well as easy to remember term. Plus, it's a cinch to pronounce and a much more positive term that than some of the others. Additionally, Double Merle is widely used among breeds other than Australian Shepherds ("lethal white" has historically been limited to Aussies). "Double Merle" also eliminates the negative connotations sometimes associated with "lethal white."

Why do some people still use the term "lethal white"?

There are various reasons. One sad fact is that most of these pups are euthanized at birth. Some people use that to justify the "lethal" part of the term.

Other people believe the term has "shock value" and use it to direct attention to the matter.

Some folks simply haven't had the opportunity to study the facts or share their lives with a homozygous merle.

How this term may be harmful ...

  1. It's inaccurate (as stated above).
  2. This term tends to be very divisive. People either like it and use it, or find it offensive and derogatory. This can lead to disagreements between people who actually all have the best interests of the dogs at heart.
  3. It propagates the myth that double merles carry defects preventing them from living long, healthy lives (see our page on Double Merles for the facts on health concerns). This can result in dogs being bypassed for adoption and ultimately, their death.
  4. In order to prevent producing double merles, people inadvertently bringing them into the world must know what the merle color pattern looks like. Education is the key. Double merle is a more effective educational term - capitalizing on the uniqueness of merle - rather than the abundance of white (remember, the parents of these pups are not white).
  5. Unfortunately, it's not only pups with "excess" white that are killed at birth. The Australian Shepherd breed standard does not require dogs to have any white at all. Regardless, some breeders feel pups with little to no white are not marketable and will kill them. Solid black males (like Bandit on our pattern white page) fall victim to this most often, even though their color is acceptable. In some breeds, certain colors or patterns are not permitted by the breed standard. The reasons are not always logical, particularly to the layman (especially since the colors may be allowed in other breeds, and often have no adverse health consequences for the dog).
  6. The term is being incorrectly used to describe any mostly white dog who is deaf, not just homozygous merles.

Lethal White in Horses

For more information on the Lethal White problem in horses, see the following sites: