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Warmblood Fragile Foal Syndrom - WFFS

Answers You Need--Warmblood Fragile Foal Syndrome

By now, you’ve probably heard about Warmblood Fragile Foal Syndrome (WFFS). While this is serious genetic disorder, and all breeding stock should be tested, it is very rare for a foal to be born with WFFS. The other good news is WFFS does not affect performance horses.

Fortunately for breeders, testing is simple and cost effective. If you know the status of the stallion and mare before you breed them, you can eliminate the chance of reproducing WFFS. There’s no need to test geldings or horses that have not or will not be bred.

Understanding WFFS

WFFS has been around for more than 170 years. It is caused by a gene mutation that impairs a normal enzyme function critical for the biosynthesis of collagen. This gene mutation is autosomal recessive, therefore two copies of the mutation are required, one from each parent, for offspring to have WFFS.

A horse is a carrier of WFFS if he or she has one copy of the mutation. Carriers do not have the disorder, but can transmit the mutation to their offspring. Carriers are not impacted as performance horses.

A carrier bred to a non-carrier, produces a carrier 25% of the time. A carrier bred to a carrier, produces a carrier 50% of the time, a non-carrier 25% of the time, and a foal with WFFS 25% of the time. It’s important to have your breeding stock tested so that you do not breed two carriers.

In most cases, a fetus with WFFS will be reabsorbed. Should a foal be born with WFFS, there are obvious symptoms, including hyperextension of the joints, fragile skin and mucous membranes, accumulation of fluid below the skin, hematomas and premature birth. Unfortunately, there is no cure for WFFS, and foals with the disorder are euthanized.


The KWPN, KWPN-NA and the NRPS now require testing of breeding stock. Fortunately, testing is simple and easy. The Veterinary Genetics Laboratory at the University of California at Davis can conduct a DNA test with a hair sample. A discounted rate of $30 is available through the KWPN-NA.

At this time, approximately 9-11% of warmblood horses are carriers. At UC Davis, 340 warmbloods have been tested, with 9% identified as carriers. Ninety-five Thoroughbreds have been tested; 4% are carriers. Forty-five Knabstruppers have been tested; 7% are carriers. Look for updated results on their Facebook page.

All of the mares and stallions at Iron Spring Farm have been tested. None of the current mares and stallions are carriers.