Lethal white (or frame overo or OLWS) is for all intents are purposes what is it named. A horse can have one copy of the OLWS gene and be fine (heterozygous for frame). A horse only is lethal if is carriers two copies (homozygous for frame)
You have to have horses with one copy in order to get horses that look like this -
The problem is, when you breed two OLWS carriers together you have a 25% chance of producing a lethal (or homozygous for rame overo) foal. The foal will not survive past 72 hours and if not humanely euthinzed, it will die a horribly, horribly painful death.
Horse can carrier the frame overo/OLWS gene and be completely solid. It is a good idea to test any horse of QH or APHA breeding to be sure of the frame overo/OLWS status before breeding.
This is a great website with lots of facts about OLWS. OLWS
I am not even going o go there with the foolish reasoning of breeding off the sire's pedigree alone... All I can say is I hope that your friend does her research and unless the colt is absolutely spectacular, that she gelds him. There are more than enough average stallions out there without adding more.
Yes, it's lethal--hence the name lethal white. And even with a "clear" sire, he should still be tested, as he can still be a carrier. Either he or the mare MUST be tested and negative if you don't want to risk the heartbreak. Breed two carriers, and you've got a 25% chance of a suffering and dying foal.
Breeders of the desireable Overo Paints live with the lethal white factor. Foal is born, lives for a day, then dies. Nothing can be done to save it. I have witnessed one lethal white. Was told by the farm owner it was the price she pays for the more desireable overos. That was a while ago, I don't know if things have changed, pretty sure the lethal white foals still die.
Waresbear, they don't have to be dying anymore. I have overos and I know who carries the OLWS gene and those horses never get bred to each other. It's only when both parents are carriers and both throw the gene that the foal dies, obviously neither parent is homozygous for it or they'd both be dead too. I breed the OLWS horses to either a tobiano or to a clear solid breedstock horse. If only one horse is carrying the gene, only one can pass it on and the foal will not die, at worst it will be a carrier.
I bought this young lady (an OLWS carrier)
To be bred to this colt (a sabino who tests clear)as soon as both are old enough:
There's no way a foal of theirs will die and I have at least a 50/50 chance of color with this mating. Even if the foal ends up breedstock, it'll be a very good looking and athletic horse. There doesn't have to be a deadly downside anymore if you're careful in the matings.
This breeder had a stallion who carried the lethal white gene (I own him now, he's a gelding), he's sired some expensive babies (one for sold for $60,000) and she bred him to outside mares but she also bred him to her own mares. After the lethal white, I asked her why she was breeding the same mare back to him. She said all better bred overos carry the lethal white gene, her next foal from the same mare was a solid. By the way, the mare that had the lethal white was solid as well. She told me no tobianos carry that gene, only solids & overos. I don't know, just what I was told by someone who paid me to ride & show their horses, I wasn't going to argue.
To clarify, though, even solids and tobianos can be LW carriers, and thus must be tested negative before being bred to another carrier. You breed two carriers together, regardless of their base color or apparent pattern, and you've got one if four odds of a lethal foal....and it's true that no vet can save them. They colic and die or you euthanize them. The gastrointestinal tracts is malformed and incomplete, as the same gene that controls the color also has a role in GI development.
And RESPONSIBLE breeders know how to get the overo color without risking dead babies.
"And RESPONSIBLE breeders know how to get the overo color without risking dead babies."
That's just it, responsible breeders test their stock. I even test my Arabians who carry the Sabino gene as that's an overo trait. I've not had a purebred Arabian test positive for the OLWS gene but if I have the negative results then I don't have to worry about crossing my half arab who does carry the OLWS gene on that particular horse.