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Lethal White Syndrome

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This frame overo sire
Special Affects and this frame overo mare

Sonny's Dainty Side, produced this frame overo filly called Dainty Affects.  A full brother who was marked the same way, and on the third breeding, a lethal.

Sonnys Dainty Side
and Dainty Affects. 

We would never had enjoyed these foals out of frame overo horses if we had been afraid to cross overo parents. 

Lethal White Syndrome is a heartbreaking birth defect, like dozens of other defects but there is no conclusive proof that it afflicts 25% of our overo horses.  More realistically, 2% to 3% of our annual foal crop is affected.  This figure is more in line with all of the birth defects that afflict animals.

It would not have been economically feasible to breed overo horses if this assertion were true. We would all be out of the overo business. This claim shouldn't be made without more conclusive testing.

These Paint horses are the result of mating an overo to an overo.  We own Paint mares and only have a few AQHA mares.  The majority of our breeding has been overo-to-overo although we avoid the loud "frame" overo-to-overo breeding.

Lethal White Syndrome Links

UC Davis 
University of Minnesota Lethal White Test Form



 OLWS - Important Update

I e-mailed UC Davis on November 7, 2000 and asked how many horses had been tested for OLWS to date, and of these horses, how many Paints had been N/N?  If a horse is tested N/N it means that they have little or no chance of producing a lethal.  The reply I got was: "There is no statistical data available on this."

Several other major universities who have been very outspoken on this subject, like the University of Minnesota, are no longer carrying information, and refer readers.  I find this extremely puzzling and feel that nearly all overo horses will be found to test positive for OLWS.  Knowing or suspecting this, what do we, as responsible breeders, do about it?

      Overo Lethal White Syndrome  or "O. L. W. S.", is a terminal defect that inevitably kills newborn foals. It is one of many birth defects that trouble breeders.  Lethal "white" foals have blue or washed out grayish eyes (not like true albinos who have pink eyes) and generally have no skin pigmentation at all, although in many cases, some foals have a touch of dark coloration here and there on the body.  We had one born with a tail that was partially black.  Other than the partially pigmented tail, this absolutely gorgeous foal was snow white.  Breeders have reported foals born with small dark spots.

    The foals initially appear normal except for their unusual coloring. They're usually breathtakingly beautiful and perfectly conformed.  The foals stand and nurse and start playing next to their mothers, like any normal foal.  Then you notice that they don't have a bowel movement after they nurse or when you give them an enema.  Signs of colic, or intestinal cramping generally begin, from one hour to twelve hours following birth, due to the foal's inability to pass feces.  The "lethal white" foal has an underdeveloped and contracted intestine.   In most cases, the intestine simply stops short of the anal opening so the food cannot pass all the way through the foal's digestive system.  This problem is caused by a failure of the embryonic cells that form nerves in the gastrointestinal system, and attempts to surgically bypass the problem have, to date, been unsuccessful. 

    In most cases, the foal will start to show signs of distress within three to five hours after birth by rolling up on their back repeatedly.  However, cases have been reported where foals go up to three days before signs are noticed.  Personally, in those cases, I feel that no one has been paying attention to what's really going on.  Depending upon the severity of the cramping and intestinal twisting, it can take several days for the foals to die on their own if no one takes pity on them and has them euthanized. 

    Lethal white foals just can't seem to get comfortable for very long.  They toss and turn, consistently showing signs of distress, and get up and down repeatedly.  That's not what normal foals do.  They suckle and play and then sleep, with the play periods increasing as the days pass and they get stronger.  It is not normal for a foal to roll and roll and roll.  It's not normal for a foal's rib cage musculature to cramp or for them to bite at their sides. 

It's not normal for them to butt their mother underneath repeatedly if they've already suckled or to switch and twitch their tails all the time (unless they're being bitten by flies) or to suck the tail tight against their buttocks.  These are signs of stress and pain.  It is not normal for a foal to roll high up on it's back, time after time.  A twist can develop in horse intestines from repeated rolling. They aren't built like we are inside. It doesn't matter whether your foal is a lethal white or a normal colored baby, this is a warning sign of possible trouble and you should call a veterinarian immediately if you see this behavior pattern developing.  Remember that it's repetitive rolling that goes on and on that is indicative of a problem, or repeated cramping along their rib cage.     

To date, no gene has actually been isolated to blame for the problem.  However, researchers have discovered a specific protein in the genes of horses who have produced lethal foals and feel this problem stems from a genetic defect.  These same cells also play a role in determining an animal's skin color.  Some of the original researchers felt that OWLS might be related to albinism as the physical signs and characteristics of severe albinism and OLWS are very similar. 

There is no treatment for OLWS because the syndrome is always fatal.  The surgery necessary to bypass the intestinal damage has never been successful, due to the extensive nature of this type of lesion. Veterinarians and professional breeder's advise immediate euthanasia for all "lethal" foals as death will inevitably occur. Your vet will not be able to tell if the foal is a "lethal" foal unless they've had extensive experience in this area, until they start showing signs of colic and stress.  There are true white foals born on occasion, so we are all reluctant to euthanize a foal until it's in distress, which can take several hours to arise, after they eat and eat and the food goes nowhere. 

    Current studies point to the theory that both parents must carry a defective gene to create this abnormality.   According to the UC Davis study, white patterned "frame" overo Paint horses who carry a certain  protein in their genes are most commonly blamed for producing the defect.  UC Davis also states that Quarter horses, Thoroughbreds, half Arabians, miniature horses, crop-outs, Paint breeding stocks and Tobianos have also produced "lethal white" foals.   

Research at the University of Minnesota and at UC Davis in California is purported to making prevention a real solution by identifying a horse's propensity for passing this problem on.  Long time breeder's will attest to the fact that breeding two frame overo horses, does not necessarily produce a lethal foal.
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Question:  If two horses must carry the gene to produce a lethal foal, how can you mate the same pair several times and have several normal foals and then a lethal foal? Do we quit breeding our good mares to good stallions out of fear?

    I find this very confusing when taking UC Davis' statements into consideration, and I've been breeding Paints for twenty years!  How much more confusing must this be for new Paint enthusiasts?  If these assertions are correct, how does this happen?  Special Affects, has sired 210 foals.  Only four of these foals were lethal whites.  Special is a "frame" overo. I had him tested in January of 2000 and he tests positive, yet he's produced nearly all normal foals.  Using the Universities findings, we would never have bred 210 foals and had 206 registered babies who have won numerous regional, national and World Championship Awards.  Years ago, we bred a mare named Sonnys Dainty Side to Special.  I was apprehensive about breeding a mare as "loud" colored as Special Affects, but the owner insisted, so we complied.  This mare's first foal was Dainty Affects, who earned nearly 300 points in Western events.  We bred Sonnys Dainty Side back to Special Affects and she had another loud colored "frame" overo stallion.  The third breeding produced a lethal.

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Ronny & Michelle Stallings

2422 Dr. Sanders Road

Aubrey, Texas  76227

(940) 365-2860