Sunday, June 17, 2007

Breeding Carriers of Lavender Foal Syndrome in Arabian Horses

I would like to calirfy a couple of things from yesterday's post, Lavender Foal Syndrome - An Arabian Horse Breeders Nightmare The foal that I was watching on marestare was euthanized early yesterday morning, I'm sorry if I left anyone thinking otherwise. Until the tests are done, the status on this foal will be that it is suspected of being the latest victim of the deadly Lavender Foal Syndrome.

To update on that foal, the owner of the foal tried to contact Cornell University but because of the weekend was unable to speak with them directly. However, the owner and vet did have the information necessary to take samples from the foal for the University's study on LFS and will be sent off post haste.

Once it is determined the foal was indeed an LFS foal, the owner will be assisting the university in obtaining samples from related horses from their herd to further assist the study. Those samples will be from both parents as well as those horses's parents and probably any siblings of any or all of these primary horses.

The more samples of related horses the university gets, the easier it will be to be for them to locate genetic indicators (or markers). While the death of this foal is tragic, it will be providing valuable input for the geneticists who will hopefully someday soon) find the responsible gene. Once the gene has been isolated then the work can begin engineering a test to screen for it.

A test to screen for possible carriers will be a huge relief to the Arabian horse breeding community. Just as the advent of the SCID (Severe Combined Immunodeficiency) test has done. Breeders of Arabian horses will be able to test their breeding stock and make informed decisions about which horses to cross without the added risk of hidden genetic killers.

That brings us to what you need to know to make informed decisions when breeding with animals that you know carry fatal traits such as LFS or SCID (this disease is recessive as well, and the following statistics and probilities etc will be the same)

Lavender Foal Syndrome is devastating to the breeder who encounters it. Not only have they lost a foal they planned and dreamed about for 11 long months but they are also left in the awkward position of having a breeding horse that is a know carrier of the genetic disorder.

Because the sydrome is considered to be recessive, one gene must be contributed by each parent for a foal to get the lethal combination that results in the expression of this rare neurological disorder.

Once a victim has been identified as having Lavender Foal Syndrome, that automatically classifies each parent as a carrier of the disorder. While it may not be possible to know which parent of the carrier horse contributed the fateful gene, there is no question that the parent of the afflicted foal is a carrier. (I'll address grandparents and direct relatives later.)

The decisions of how to breed carrier horses are based pretty much on the odds. If you have a know carrier, you know that that carrier statistically will contribute that affected gene 50% of the time. That should translate to half of that horse's offspring will also be carries, however, Mother Nature is not that co-operative.

Just like the flip of the coin, odds may hold out over millions of test but can vary greatly in small increments. This translates to each time you breed to that horse to a NON-carrier you have a 50-50 chance you will get a carrier foal. But you also have that same chance you will produce a clear foal. There is no chance, breeding to a non-carrier of producing a lethal foal.

It does not mean half the foals will be carriers and half will be non-carriers. Good example my mare, Aana, who has had 5 colts in a row, statistically she should have given birth to an even mix of colts and fillies. Aana has defied the odds. Odds are only odds, not specifics.

So the question is, if you breed a carrier to a carrier what are the chances? Breeding two carriers there is a 25% chance the mating will produce a non-carrier. There is a 50% chance of producing a carrier. There is a 25% chance of producing a lethal foal.

More on LFS to come!

Because it is so rare, there are few cases to study to garner data needed to establish reliable information. Anyone having or who knows someone who has had a lavender foal is requested to contact researchers to help find and isolate this killer of Arabian Foals.
For more information on Lavender Foal Syndrome


  1. Thank you for the information on LFS. Such a tragic syndrome - to find out that both the dam and sire are carriers of the gene when a foal is born with LFS is devastating. I pray that being able to gather samples from both the dam and sire and siblings will indeed help to find this gene/marker and thus a test to be developed to determine if an Arabian horse is a carrier. Thank you MiKael, for your always informative and professional blog entries.

  2. wow, I remember vaguely hearing about LFS.

    Thanks for giving me a learning lesson!

    Very good post-thnx!

  3. Wow MiKael.

    This sounds like the Lethal White syndrome in the Overo Paint Horses. Although in this case the babies rarely survive past a few days old. It is dreadful.

    I hope you are feeling better, we seem to be still existing a parallel life LOL. I am much better although my neck is still terribly stiff and I cant turn my head to the left without pain, but at least the headache has gone and the nausea. Did you have a similar bug??

    I hope you sorted the Rachel problems out successfully and all is running smoothly again. When is your open house?



  4. Very interesting. I had never heard of LFS. You always do a great job of educating you readers. Thanks MiKael.