According to Animal Genetics Inc., Warmblood Fragile Foal Syndrome (WFFS) is an autosomal-recessive trait, meaning a foal can only be affected if that foal inherits the disease from both parents. Parents that are carriers do not have any symptoms associated with WFFS. However, they will pass on a copy of the defective gene to their offspring 50% of the time whether bred to a carrier or a non-carrier and regardless of the foal’s gender. If two carriers are bred, the foal has a 25% chance of being affected (a death sentence) and a 50% chance of being a carrier. (Feel free to research this further on your own. I have, but did not want to get bogged down in such matters due to the points I am trying to make.)

My understanding is that, in March of 2012, a mare that gave birth to a foal with all the symptoms currently associated with WFFS was at first thought to be a carrier for a different genetic disease, such as Hereditary Equine Regional Dermal Asthenia (HERDA, which was discovered in 2007). When she was found to not be a carrier, research of her and some of her relatives led to the identification of the genetic anomaly responsible for WFFS.

A genetic test for Warmblood Fragile Foal Syndrome Type 1 (WFFS), developed by N. Winand, became commercially available in 2013.

There is no way of knowing the exact numbers of WFFS cases prior to the test due to possible misdiagnoses, and there is no way of accurately predicting the number of cases since the test due to misdiagnoses and very limited testing of aborted fetuses that may be linked to the syndrome.

Detailed information about the prevalence of the WFFS mutation is not readily available; however, random samplings of 124 horses (used in the patent application for the genetic test) and 500 warmbloods in Germany (study by B. Gunreban) showed carrier rates of 11.11% and 9.5% respectively. Let’s say 10%, shall we?

Update: This percentage is at best a guess in today’s gene pool, and is likely higher than it was 5 years ago. It may be seen as a ‘rare’ condition, but assuming that the percentage will stay the same and not increase without intervention is simply uninformed.

What If #1

Let’s assume there are 4,000 warmblood breeding stallions worldwide (alive or deceased and available through frozen semen) and an equal number of breeding mares. (If you want to argue about the actual numbers here, you will miss the point.)

Let’s further assume that 10% of them are carriers of WFFS. That would mean that 400 of the stallions are carriers and 400 of the mares are carriers. Agreed?

Now let’s say that each carrier stallion averages 100 foals over a decade and that each carrier mare averages 6 foals over that time span. (Again, if you want to argue about the actual numbers here, you will miss the point.) Given these numbers, each carrier stallion will have sired 50 carriers, whether he was bred to a carrier mare or not, and each carrier mare will have produced 3 carriers, whether bred to a carrier stallion or not. If a carrier stallion and a carrier mare are mated, they will produce 50% carriers and 25% foals with WFFS. That’s how autosomal recessive syndromes work.

So, from our 400 carrier stallions we now have 40,000 offspring, half of which, 20,000, are carriers. Since most of the matings will likely be warmblood to warmblood, we will not add the offspring of the mares to our totals in this What If scenario.

Not all of the offspring will be breeding stock, but half will be male and half will be female. So, let’s assume that 20% will be stallions, 30% will be geldings and that all of the fillies will become broodmares. That leaves us with 4,000 new carrier stallions (20% of the 20,000 carrier offspring) and 10,000 new carrier broodmares (50% of the 20,000 carrier offspring).

Now let’s pretend that, in that same decade, half of our original stallions are no longer available for breeding through fresh or frozen semen. Fair? And let’s pretend that none of the original mares are still producing. Reasonable?

Looking at the subsequent decade, we have 4,200 (200 + 4,000) carrier stallions and 10,000 carrier mares. Please note that the number of carrier stallions now exceeds the total number of stallions assumed to be in the genepool currently. We can again assume that each stallion will sire 100 foals over the decade and that 50% of them will be carriers. That gives us 21,000 new carriers (half of 42,000 foals) in our second decade.

Of course, there has been no mention of affected foals if a carrier is bred to a carrier because they will not enter the gene pool. But do keep in mind that as the percentage of carriers increases so does the likelihood of breeding a carrier to a carrier.

Can you see how the numbers and percentages of carriers will increase and that just breeding a carrier to a non-carrier will not halt the progression of WFFS?

What If #2

What if all the warmblood breeds, studbooks and registries made testing mandatory? And what if they all decided not to license any new stallions that were carriers, to not approve any new mares that were carriers and not register any foals that were carriers? (Geldings and spayed fillies would be exempt.)

Update: This possible course of action does not restrict any bloodline nor cause it to be lost. Only the carriers from any given line would be ineligible for registration unless not capable of reproduction. It also does not force anyone to have their breeding stock tested. It does force them to have the offspring tested if they want to register them.

Of course these policies would have to apply to all of the regulatory bodies or there would likely be dizzying shifts from registry to registry. By applying these new rules from this point onward, there would be no forced removal of any breeding stock, but there would be incentives to breed for non-carriers!

How long do you think it would take before the gene pool was clear of the mutation? One decade? Two decades?

Discussion

Please compare the two What Ifs and, by all means do your own research and calculations. You might even want to look at what has happened in the past regarding autosomal-recessive syndromes in horses. Pay particular attention to what has happened once a condition was identified, tests were made available, education was provided and the governing bodies did not take immediate and firm action. See how many of those that were identified decades ago are still in the afflicted gene pools today.

By all means discuss these topics with others. As for me, I am very sad, because I have a strong suspicion that What If #2 will never even be considered.

Please read the replies, and feel free to add your own.