Warmblood Fragile Foal Syndrome in Horses: WFFS Signs and Genetic Testing
- See your vet immediately if a newborn foal has very thin, stretchy, tearing skin, open skin lesions, floppy ears, marked joint laxity, or is born premature and weak.
- Warmblood Fragile Foal Syndrome, often called WFFS or FFS type 1, is an inherited connective tissue disorder linked to a PLOD1 gene mutation.
- Affected foals are born with two copies of the mutation. Horses with one copy are carriers and usually look normal but can pass the variant to offspring.
- DNA testing is used to identify carriers and confirm suspected cases. Hair roots are commonly used for testing.
- Breeding two carriers together creates an average 25% risk of an affected foal, 50% risk of a carrier foal, and 25% chance of a clear foal.
What Is Warmblood Fragile Foal Syndrome in Horses?
Warmblood Fragile Foal Syndrome, also called WFFS or fragile foal syndrome type 1, is a fatal inherited connective tissue disorder in horses. It is best known in Warmblood and sport horse lines. Affected foals are born with abnormally thin, fragile, hyperextensible skin and mucous membranes that can tear with normal handling, pressure, or even before birth.
This condition is present from birth. Reported signs include open skin lesions, floppy ears, unusually loose joints, fluid accumulation, bruising, and premature delivery. Because the tissue defect is severe and widespread, many affected foals are stillborn, nonviable, or euthanized shortly after birth for welfare reasons.
WFFS matters to pet parents and breeders because carrier horses usually appear completely normal. The problem often becomes visible only when two carriers are bred together and a foal inherits two copies of the mutation. That is why genetic testing is such an important part of prevention and breeding planning.
You may also see the condition referred to as FFS type 1 rather than WFFS. The newer name reflects that the mutation has been identified in some non-Warmblood breeds too, although it remains most relevant in Warmblood and sport horse populations.
Symptoms of Warmblood Fragile Foal Syndrome in Horses
- Very thin, stretchy, fragile skin present at birth
- Open skin tears or raw lesions
- Loose or hyperextensible limb joints
- Floppy ears
- Hematomas or bruised swellings
- Seromas or fluid pockets under the skin
- Subcutaneous emphysema or crackly swelling under the skin
- Hydrops or marked fluid accumulation associated with pregnancy
- Premature birth, stillbirth, or a very weak nonviable foal
See your vet immediately if a foal is born with tearing skin, large open lesions, severe weakness, or obvious tissue fragility. These are not normal newborn findings. WFFS is uncommon, but it is a true emergency because affected foals are often painful, vulnerable to infection, and may not be viable.
Not every foal with skin lesions has WFFS. Other inherited and non-inherited conditions can look similar, so your vet may recommend exam findings, photos, pedigree review, necropsy if the foal does not survive, and DNA testing to sort out the cause.
What Causes Warmblood Fragile Foal Syndrome in Horses?
WFFS is caused by an inherited mutation in the PLOD1 gene. This gene helps the body make normal collagen, which is a major structural protein in skin, ligaments, tendons, and other connective tissues. When the mutation is present in two copies, collagen support is abnormal and tissues become fragile.
The condition is inherited in an autosomal recessive pattern. That means a foal must receive one mutated copy from the sire and one from the dam to be affected. Horses with only one copy are called carriers. Carriers are not expected to show clinical signs, but they can pass the mutation to their offspring.
If two carriers are bred, each pregnancy has an average 25% chance of producing an affected foal, a 50% chance of producing a carrier, and a 25% chance of producing a foal with no copies of the mutation. Those percentages apply to each pregnancy separately.
The mutation is most relevant in Warmblood and sport horse populations, where reported carrier frequency has been around 9% to 11% overall in tested Warmbloods. Studies have also identified the allele in some other breeds, including Thoroughbreds at a much lower frequency, which is why breed-specific testing recommendations matter.
How Is Warmblood Fragile Foal Syndrome in Horses Diagnosed?
Diagnosis starts with your vet’s exam of the foal and the foaling history. WFFS is usually suspected when a newborn has thin, hyperextensible skin, open lesions, floppy ears, and unusually loose joints, especially in a Warmblood or sport horse pedigree. Some cases are recognized after stillbirth, abortion, or the birth of a nonviable foal.
A definitive diagnosis relies on genetic testing for the known PLOD1 mutation. Testing can be performed on hair roots, blood, or appropriate tissue samples, depending on the lab and the situation. If the foal has died, your vet may recommend necropsy plus DNA testing, because appearance alone may overlap with other connective tissue disorders.
This distinction matters. Conditions such as HERDA and other causes of neonatal skin fragility can look similar, so a visual exam by itself may not be enough. Genetic confirmation helps your vet guide the breeding plan for the mare and stallion, and it can help related horses be tested appropriately.
For healthy adult horses, diagnosis usually means carrier screening, not illness workup. A normal-looking mare or stallion can still be a carrier, which is why pre-breeding DNA testing is the most practical way to reduce risk.
Treatment Options for Warmblood Fragile Foal Syndrome in Horses
Spectrum of Care means you have options. Here are treatment tiers at different price points.
Budget-Conscious Care
- Urgent farm call or clinic exam for the newborn foal
- Pain and welfare assessment
- Basic wound protection and gentle handling guidance
- Discussion of likely prognosis based on severity
- Targeted DNA sample collection for the foal or parents if feasible
Recommended Standard Treatment
- Veterinary exam and stabilization attempt if the foal is alive
- Analgesia, bandaging, nursing support, and infection-risk management as appropriate
- DNA testing of the foal and often the sire and dam
- Breeding-risk counseling for future matings
- Humane euthanasia discussion when suffering is significant or survival is not realistic
Advanced / Critical Care
- Referral hospital evaluation for a live foal
- Intensive wound care, IV fluids, nursing support, and critical care monitoring
- Comprehensive diagnostics, including bloodwork and confirmatory genetic testing
- Necropsy with tissue submission if the foal dies or is euthanized
- Expanded herd or breeding-program screening and genetic consultation
Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.
Questions to Ask Your Vet About Warmblood Fragile Foal Syndrome in Horses
Bring these questions to your vet appointment to get the most out of your visit.
- Do this foal’s skin and joint findings fit WFFS, or are other conditions also possible?
- What samples should we submit for genetic testing: hair roots, blood, or tissue?
- Should we test both the mare and stallion even if they look completely normal?
- If one parent is a carrier, what does that mean for future breeding plans?
- Would necropsy add useful information if this foal does not survive?
- What is the expected turnaround time and cost range for WFFS testing through the lab you use?
- Are there related horses in our program that should also be screened?
- How can we avoid affected foals while still preserving useful bloodlines and genetic diversity?
How to Prevent Warmblood Fragile Foal Syndrome in Horses
The most effective prevention is pre-breeding DNA testing. Because carriers usually look healthy, you cannot reliably identify risk by appearance alone. Testing potential sires and dams before breeding helps your vet and breeding team choose pairings that avoid producing affected foals.
In practical terms, the key step is to avoid carrier-to-carrier matings. Breeding a carrier to a horse that tests negative for the known mutation should not produce an affected foal, although about half of the offspring may be carriers. That makes recordkeeping and transparent communication especially important for future breeding decisions.
Testing is currently recommended for Warmblood and sport horse populations, and it may also be appropriate in non-Warmblood breeds where the allele has been detected. Many labs use hair samples with intact roots, which makes screening relatively straightforward and affordable compared with the emotional and financial cost of an affected pregnancy or foal.
Prevention is not about eliminating every carrier from breeding overnight. A more balanced goal is to work with your vet and breed advisors to make informed mating choices that protect foal welfare while also considering long-term genetic diversity in the population.