Sherry’s Blog - Summer 2018

Sherry Scott MBE invites Lynne Crowden of Woodlander Stud to share an insight into Warmblood Fragile Foal Syndrome.

Lynne Crowden

Warmblood Fragile Foal Syndrome (WFFS) is a genetically induced disorder seen in horses, specifically those belonging to the Warmblood breeds. Affected foals have extremely fragile skin that tears or cuts from contact with normal surroundings, are subject to infections, and are often euthanized within a few days of birth. The disease is caused by a mutation of a gene and is incurable.

The disease is caused by a mutation in the PLOD1 gene, which is important for an enzyme, which supports the biosynthesis of collagen, which then affects the skin and mucous membranes. Humans may suffer a similar defect known as Ehlers-Danlos Syndrome.

Two copies of the mutated gene are needed to cause the disorder and if both parents, otherwise completely normal, are carriers, there is a chance, using normal genetic probability, for 25% of their offspring to be affected and 25% to be carriers while 50%, implicitly, will be unaffected. The incidence of carriers is estimated between 6% and 10% in Warmbloods, but this is based on very limited data. There is also a low carrier frequency in Thoroughbreds.

The condition was first identified in the mid 90s but has only recently become topical as so few live foals were available to be diagnosed. One of the first diagnosed cases was a foal born in the USA in 2012 and the research was published in 2015 in a veterinary research journal. Following a further case this year, a reaction to the implications of WFFS for the breeding population is now converting to sensible consideration of what needs to be done for the future of breeding.

The KWPN has announced that only 4% of its riding horse stallions, presumably only those tested, are carriers. So let’s say that, typically, 5% of stallions, i.e. 1 in 20 and 5% of mares (there is an equal incidence) i.e. 1 in 20 mate, what is the statistical probability of two carriers actually mating? The risk, I believe is low. Then factor in the fact that 50% of the resultant offspring will be completely unaffected and of the remainder a further 25% will by carriers only.

The issue is to identify carriers in the mare and the stallion population and to ensure that they are not bred together. It is important to compare this risk with many other potential genetic defects which lead an animal to being non functional and having either a short or poor life.

We should take steps. At Woodlander Stud we tested our own stallions and discovered that Woodlander Wild Child is a carrier. We immediately started the process of testing, free of charge, the mares booked to that stallion. I believe this is the responsible process. While breeding with one carrier will pass on the recessive carrier gene and, on average 50% will be carriers, breeding with two carrier parents results in 1 in 4 of deceased or aborted foals.

So, the issue is only that two carriers do not mate. In time, I imagine that all studbooks and responsible studs will announce the status of their stallions, and breeders will also test their mares as a matter of course. The test is under £40 in the UK.

Information taken from publications including:
Animal Generics UK; Cystic-Fibrosis-Carrier-Screening:
WFFS: UC Davis; Eurodressage

– Statement of the American Hanoverian Society

It would be a pity if an over reaction to this very unpleasant condition affected the breeding with otherwise valuable genetic material. The incidence of, say, cystic fibrosis in humans has an almost identical risk with a 25% chance of two carrier parents producing an affected child. Very few couples would genetically test and while this is a challenging and terrible disease, it is not prevalent. Let’s be open, honest and sensible and keep British Breeding on its upward trajectory.