4 T Horses Ranch
Leathal White Overo VS Cremellos and Perlinos- related or not?
Lethal Whites VS Double DilutesBy Tracy Steele
Many times I have talked to someone who thought that a palomino to palomino, or other Crème to Crème cross (that can result in a cremello or perlino foal,) could result in a lethal white foal. "But I KNOW so-and-so had an all white baby out of two palominos and the foal was a lethal white- it died!" Before we go further, let's define what a lethal white foal is. It is an all-white foal that dies, not long after birth (hours or days) due to complications from intestinal tract abnormalities, caused by a genetic defect. UC Davis has identified the one gene responsible for this genetic defect, so lets examine what they have to say about it. The UC Davis web site states this about the appearance of a lethal white foal:
"A lethal white overo foal lacks black pigment in the skin. Foals have blue eyes, white hair and pink skin, but may have small pigmented skin spots or a few colored hairs."
This DOES sort of sound like the description of a cremello or perlino
horse, (minus the small pigmented spots or colored hairs of course)
doesn't it? But there IS a difference in the foal appearance.
Cremello and perlino foals are born a very light crème color, with
blue eyes and pink skin. However, since they have crème colored
hair, and NOT white, you can easily see any true white markings, such as socks, blazes, etc. (see picture #1, a cremello colt.)
Now, you may be thinking, "Yes, but what about the lethal part of it? What does it matter if they LOOK a little bit different?" Well the differences between lethal whites and double dilutes do NOT stop with appearances. The genetics behind them are completely different. Lets take a look again at what UC Davis has to say-
UC Davis has identified the ONE and ONLY gene responsible for producing the lethal white syndrome. It is associated with horses that carry the overo paint gene. Overo is much more complex genetically than the tobiano coloring gene. There are many different genes that can combine to produce an overo foal. Just ONE of these overo genes is responsible for lethal whites. The gene responsible for the lethal white foals has been named "Lethal White Overo" (LWO). Another description from UC Davis- "The spotting pattern in horses with the LWO gene generally corresponds to the frame overo pattern, with white markings on the head and sides of the body, not necessarily on the legs, the belly or the dorsal midline. However, it has also been found in some tobiano/overos, in some solid-colored (breeding stock Paint) offspring from overo matings, and in some tobianos and Quarter Horses without obvious evidence of the overo pattern." Did you notice that they mentioned nothing about what color these horses were; sorrel, palomino or otherwise? The reason is that this gene is not linked with a coat color. It is linked to a gene that CAN cause an overo spotting pattern in a horse that would have otherwise been solid colored, but does not always do so. (Overo is so complex genetically, that no one is exactly sure why the gene does not consistently produce spots.)
So, what does this LWO gene have to do with the cremellos? The answer is- absolutely NOTHING. The LWO gene is NOT the same gene that creates double dilutes. I call Cremellos and Perlinos "double dilutes" because that is exactly what they are. They look the way they do because they received two copies of the Crème dilution gene (double that of a palomino or bucksin: one from each parent). They are NOT lethal whites that somehow managed to survive.
To prove this point further, let's look at what these two different genes do to a horse in their single and double forms.
The LWO gene in its single form (heterozygous- only one parent passes the gene on) can produce the "frame overo" paint pattern, or can even be hidden in an otherwise solid looking horse (such as a quarter horse- this is one of the genes responsible for "crop-outs"). LWO in its homozygous form (two copies of the gene-one from each parent) produces an all white foal that always dies (Lethal White.)
The Crème gene in its single form dilutes the coat color on a horse that would have been a sorrel, into a palomino, and what would have been a bay, into buckskin. (Please see www.doubledilute.com for great color charts and more information on color possibilities.) The Crème gene in its homozygous (double) form produces dilutes the coat and eyes even further, producing Cremellos and Perlinos. These horses are 100% normal and viable, and cannot ever produce a sorrel or bay no matter what they are bred to. In that way they are similar to the homozygous tobianos. Just as a homozygous tobiano is homozygous for the tobiano spotting pattern, thus producing a paint no matter what it is bred to; cremellos and perlinos are homozygous for the Crème gene. This is why people who love the crème colors, and have done the genetic research on these horses, are so excited about them. Just as a homozygous tobiano is valuable to a paint breeder because of the spots guarantee, a cremello is valuable to a palomino or buckskin breeder because of the COLOR guarantee.
Ok, but you STILL just KNOW you heard of a cremello colt from resulting from the mating of two solid (non-overo) palominos, dying- a lethal white. I offer you two possibilities.
1. Since the LWO gene can be hidden in solid colored horses, (OF ANY COAT COLOR- palomino, bay, black gray; they could all carry the LWO gene) two solid Crème horses- (palomino or buckskin) who ALSO happened to carry the LWO gene, COULD, in theory, produce a cremello or perlino foal that ALSO got a copy of the LWO gene from each parent. That would be the only way you could get a true lethal white cremello from a "non-overo" breeding. (Note- I say "non-overo" because the horses would look solid- so not "overo" to the eye- but would still carry the Lethal white overo gene) This would be a million in one thing, but "it could happen," as it could with ANY colored horse.
2. The foal was not a truly a lethal white after all, but instead died suddenly and unexpectedly from grass tetanus, colic, or some other ailment. However, because of it's light coloring, instead of looking for another reason for its death, it was instead written off as a "lethal white". Lack of education on the part of the breeder/foal owner is the main culprit in this (the most likely) situation. There are many myths and misconceptions out there. That, coupled with the rarity of these colors, makes correct information on these horses harder to find, and misinformation easier to believe.
Now, that you've had a chance to examine the facts we've worked hard to gather, I hope you can see that trying to blame the crème gene for lethal whites would be like trying to blame it on the gene that creates black horses, or sorrel horses, or dun horses. Why? Simply put, it's because the lethal white overo gene is found in ALL colors and even several breeds. (Side note-Any breed that can have the overo coloring also has the possibility of having the LWO gene.) Cremellos and perlinos are just like any other colored horse out there. They are NOT more inclined to carry LWO or any other genetic disease. Research shows it is not any certain coat color that needs to be held responsible for the tragedy of lethal white foals. Just one gene is responsible for the syndrome, LWO, and it is colorblind: not prejudiced towards, nor linked to, one color, Crème or otherwise.
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