Breeders can supposedly eliminate the possibility of having a lethal foal by testing their breeding stock and never crossing horses who both carry the suspect gene, however, if we had used this test as the basis for our decision, Dainty Affects and her brother would probably never have been born, so I think we all need to use some common sense here.  I personally feel that 98% of all overo horses will test positive as I have talked to very few breeders who have not had lethal foals out of their stallions or mares. 

    I am confused on this issue since you can breed the same pair several times and never see a lethal.  According to the study, my stallion must have the gene and the mare must have the gene or they would never have produced a lethal in the first place.  So….if they're carrying the gene, why did two of the three foals have no defect?  It seems to me that either they will or will not produce a lethal every time, if bred the same way, if the study is to be believed, so I am raising an eyebrow at this point in time, until a lot more research is done. 

    UC Davis announced their discovery of a mutant gene that appears in DNA strands of horses who have produced lethal white foals.  They stated that 25% of matings between overo-to-overo horses result in lethal white foals.  That was my understanding when I read the information in January of 1999.  UC Davis admits they have no conclusive proof that this gene is actually responsible for the syndrome, only that it is present in horses who have produced lethal white foals.  UC Davis prints a disclaimer stating that "lethal white foals can also occur from mating with Quarter horses, tobianos and breeding stock horses," as this gene is present in their DNA as well.  IF this is true, then we have beaten the statistics and most of the breeders I know, are in the same boat, or they would not be in business if 25% of their foals are lethal white foals and another 10% to 40% are solids! 

    I finally acquired the data from UC Davis on the numbers of horses they had tested before publishing their study.  Only 700 horses had been tested at UC Davis for the Lethal White Syndrome, as of January 1999.  UC Davis said that most tests were from horses who had produced a lethal white foal.  This bothered me, so I called the APHA for some more statistics to conduct my own study. Over 87,000 mares were bred and reported on American Paint Horse Association Stallion Breeding Reports in 1997-1998, to nearly 15,000 approved stallions, totaling 102,000 breeding animals.  There had been over 500,000 Paint horses registered to date.  The APHA cannot forward relevant breeding statistics to UC Davis, as they have not yet developed a "follow-up"  breeding form that requests a stallion owners' report on the results of mating, so the accuracy of the 25% statement from UC Davis was based on testing 700 horses. 

    I am not, in any way, trying to belittle the wonderful efforts these universities are making.  What concerns me is the reporting from UC Davis which gives the general  public is the impression that 25% of our annual overo foal crop dies within a few days of birth!  That's just not true, and I'm sure that UC Davis is not aware that most people think that's what they're saying, and this is impacting the overo industry negatively.  Overo-to-overo mating can definitely result in a lethal white foal, and the overo doesn't necessarily have to be a "frame" overo, either. 

    The last lethal white foal I saw was sired by a very minimum colored Paint stallion whose sire was a Three Bars bred Quarter Horse and whose dam was sired by a frame overo and out of a quarter horse.  The dam of this foal was a black breeding stock mare whose mother was a purebred bay thoroughbred mare and whose sire was by a frame overo stallion and out of a black Quarter Horse mare.  The resultant foal carried very little Paint genetics and it's tail was nearly all black, but it still died. 

    Most long-time breeders agree that only about 1% to 2% of all overo-to-overo mating produces lethal white foals unless you're breeding horses whose lineage has a proven record of producing lethal foals.  This is a more realistic representation of the nominal percentage of all birth defects of varying kinds that are reported across the entire equine industry.

    MY CONCLUSION: 
There are many types of birth defects.  This is one of many.  I'm not trying to trivialize this situation, but present facts on the subject, based on over 20 years of breeding overo horses in this industry.  I really feel that the researchers should simply call this birth defect "Lethal White Syndrome" and leave the word "overo" out of the mix, since, by their own admission, several other breeds of horses produce lethal white foals, including tobiano horses.  I can only give you a personal observation that there is one bloodline in the Paints that I personally shy away from because they have consistently been seen to throw lethals. 

    I breed anything with Painted Robin bloodlines only to AQHA or JC stallions as this is the line that, after years of observation, seems to have a tendency to throw a lot of lethal foals.  Painted Robin was a quarter horse crop-out who carried the bloodlines of the strongest white producing AQHA sires in the industry: Leo, Sugar Bars, Skipper W and Plaudit.  The photographs I've seen of him indicate that he may have had an equine form of "Down's Syndrome" as he displayed many characteristics.  Oversize head, slanted eyes and ears.  He was almost all white. 

    In conclusion, breeding Paint horses is a gamble, regardless of how much research you do, or how many tests are available, but we're the fastest growing breed in the World because our best horses are like diamonds… difficult to attain, but well worth the effort, emotionally and financially.  You can reduce the risk of producing a lethal foal by breeding loud colored frame overo mares to AQHA or Jockey Club registered stallions, or vice versa.  Your color percentage will be awful, but you'll be safer. 

    When in doubt as to how to proceed, this course of action is what I would suggest.  As for me, since we've had only 3 lethals born here in over 20 years, I shall keep breeding overos responsibly as we've always done, and cry when the mix doesn't work.  Hope this has helped inform you.  Please contact me if you have any comments or questions.

MICHELLE STALLINGS
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