Fragile foal syndrome type 1

FFS weakens the skin, tendons and other tissues that support the body

Skin, tendons and other tissues depend partly on collagen for their strength. Think of collagen as fibers that help tissues hold together when stretched or loaded. The PLOD1 gene provides instructions for an enzyme, a protein that helps produce collagen.

The variant tested for in type 1 FFS is PLOD1:c.2032G>A. Two copies severely disrupt connective tissue function. This is more than sensitive skin or an injury caused by rubbing: the tissues themselves lack their usual resilience. Explaining the underlying defect also helps distinguish the inherited condition from an ordinary wound.

References [1] · [3]

FFS can cause fragile skin and open wounds at birth

In liveborn affected foals, skin may be unusually thin, stretchy and easy to tear. Mucous membranes, which line some body cavities, can also be involved. Extensive open wounds and excessively flexible joints have been described. Some foals also have bruising or abnormal fluid accumulation.

Injuries can develop before delivery, so a newborn’s lesions are not necessarily injuries sustained during birth. Their distribution varies, and no single feature identifies FFS by itself. This differs from the situation of a one-copy carrier, which is not expected to show this disease.

References [2] · [3]

FFS can be associated with abortion and stillborn foals

FFS can also present as abortion, stillbirth or premature delivery. A study published in 2025, using records of pregnancies that had already taken place, found more pregnancy and foal losses in matings between two carriers than in the other mating groups examined.

The study involved one stud farm and relatively few carrier-to-carrier matings. It did not find increased embryonic losses before day 42 of pregnancy in that group. Its findings therefore do not establish FFS as the cause of every early loss, and its outcome percentages cannot be used as a prediction for any individual mare. Genetic probabilities and observed pregnancy outcomes answer different questions.

References [5] · [3]

FFS can affect several breeds, including Thoroughbreds

WFFS stands for Warmblood Fragile Foal Syndrome. The name still appears in laboratory reports and older records, but the condition is not exclusive to Warmbloods. A genetically confirmed affected Thoroughbred has been reported.

The variant has also been identified in Knabstruppers, American Sport Ponies and Haflingers. Finding carriers in a population is different from documenting affected foals there. Published frequencies depend on which horses and families were sampled; they do not tell you the result for one horse. Equally, a breed absent from a published list is not automatically proven free of the variant.

References [1] · [4]

Fragile skin alone cannot confirm a diagnosis of FFS

A vet considers the lesions, whether they were present at birth, the pregnancy history and information about both parents. Other connective tissue disorders can resemble FFS. HERDA is one example, although it involves a different gene and its signs often become apparent later.

Examining tissue, sometimes after the foal has died, can guide an investigation without necessarily identifying the cause on its own. The targeted PLOD1 test can establish whether two copies of the FFS-associated variant are present. A vet and laboratory can advise on suitable samples and preservation; photographs alone cannot replace that investigation.

References [3] · [4] · [2]

FFS DNA testing distinguishes unaffected carriers from foals with FFS

The test looks for the specific variant associated with type 1 FFS. It distinguishes no detected copy, one copy and two copies, as explained below. A horse with one copy can pass it to a foal, but does not have FFS. To develop this disease, a foal must inherit two copies of the variant, one from each parent.

A negative result addresses the tested variant within the test’s limits. It does not rule out every cause of fragile skin, developmental abnormality or pregnancy loss. Laboratories may use different letters in their reports. Read the laboratory’s own key and check that the report belongs to the horse in question, rather than assuming that one letter has a universal meaning.

References [1] · [3]

No treatment restores normal tissue strength in a foal affected by FFS

There is no curative treatment that restores normal tissue strength in a foal affected by FFS. Injuries may be extensive and incompatible with an acceptable quality of life. Liveborn cases described in clinical resources are generally euthanized soon after birth because of the severity of the condition.

A newborn with unusual tissue fragility or major wounds needs prompt veterinary assessment. The vet assesses pain, prognosis and welfare decisions in the individual case. The severe outlook for affected foals should not be applied to an adult with a single copy: carrier status is not, by itself, a diagnosis of illness.

References [2] · [3] · [4]

Preventing a foal from inheriting two copies of the variant responsible for FFS

FFS follows autosomal recessive inheritance: a foal is affected if it receives one copy of the variant from its dam and one from its sire, whether the foal is male or female. If the mare and stallion each have one FFS variant copy, every conception has a 25% chance of an affected foal with two copies, a 50% chance of an unaffected carrier with one copy and a 25% chance of a foal without this variant. Four pregnancies need not produce exactly that distribution, and those proportions do not describe liveborn foals alone.

If one parent has one FFS variant copy and a DNA test confirms that the other has none, their foal cannot inherit two copies and will not have this form of FFS. Each conception still has a 50% chance of a foal inheriting one copy and becoming an unaffected carrier. Knowing both results allows breeders to avoid at-risk matings without automatically removing every carrier from a population. Other health considerations and genetic diversity remain part of the breeding decision.

References [1] · [2] · [5]

Questions about the condition: Fragile foal syndrome type 1

Scientific sources about the condition: Fragile foal syndrome type 1

This article brings together the research and the university and laboratory resources listed below. Numbers after each section link to the references used. Sources consulted in November 2026.

1. 1.
   Fragile Foal Syndrome (FFS) Type I

   UC Davis Veterinary Genetics Laboratory · Test documentation

2. 2.
   Fragile Foal Syndrome Type 1

   UC Davis Center for Equine Health · University resource

3. 3.
   Monthoux et al. (2015) — Skin malformations in a neonatal foal tested homozygous positive for Warmblood Fragile Foal Syndrome

   BMC Veterinary Research · University of Zurich · Research

4. 4.
   Grillos et al. (2022) — First reported case of fragile foal syndrome type 1 in the Thoroughbred

   Equine Veterinary Journal · UC Davis / Royal Veterinary College · Research

5. 5.
   Kehlbeck et al. (2025) — Warmblood fragile foal syndrome: Pregnancy loss in Warmblood mares

   Equine Veterinary Journal · University of Veterinary Medicine Hanover · Research