The KWPN has decided to test all active KWPN-approved stallions for WFFS. The breeding season is in full swing and breeders now make the stallion choices for their mares. By publishing the WFFS status of the KWPN-approved stallions we want to inform breeders optimally.

Recently, there has been a lot of publicity around WFFS, the Warmblood Fragile Foal Syndrome. But there is still a lot of unrest about this, for Dutch breeding, new condition. Recently it was discovered that three KWPN approved stallions carry the WFFS gene. It is currently not transparent which other approved stallions might carry the WFFS gene, as they have not been tested. Therefore it has been decided that all actively covering KWPN-approved stallions will be examined for WFFS. The stallion owners have been informed about the testing of the KWPN-approved stallions. The test is expected to take two to three weeks, after which the results (carrier or no carrier of the WFFS gene) per stallion will be published on

Recently, at the initiative of the KWPN, a test was made available in the Netherlands by the Van Haeringen Laboratory. A foal with WFFS always has a sire and a dam who are a carrier. The KWPN now starts testing the KWPN approved stallions. Then we will evaluate how to integrate the screening of mares in the breeding program. In addition, we want to investigate the possibilities to integrate the WFFS test into the already existing tests at the KWPN.

There is still a lot of uncertainty about WFFS. We therefore presented the most frequently asked questions to Prof. Marianne Sloet of Oldruitenborgh-Oosterbaan, professor of internal medicine of the horse at the Faculty of Veterinary Medicine of Utrecht University, dr. Ir. Bart Ducro, Assistant Professor of Farming & Genetics, Wageningen University and Johan Knaap, KWPN Director of Breeding & Innovation.

Frequently asked questions

What are the symptoms of WFFS?

Prof. dr. Dr. Sloet: "The Warmblood Fragile Foal Syndrome is a hereditary disorder that has been recognized in the United States for several years. A foal with WFFS can be aborted, be born prematurely and/or be born with abnormalities. The most important abnormalities in the newborn foal are: skin abnormalities (such as too elastic skin that tears easily, wounds that 'just' occur) and hyperextension of joints. Usually the animals will die within 1-2 weeks of birth or they need to be euthanized."

How extensive is WFFS in the Netherlands?

Sloet: "Nothing is known about that yet, we can only know after we have tested a sufficient amount of horses."

Are there any foals in the Netherlands where WFFS has been diagnosed?

Sloet: "No, in the Netherlands there is not a single foal in which WFFS has been proven, but some foals have been reported of which there is a strong suspicion that it was WFFS based on the clinical symptoms. From one foal we have material that is being tested at the moment, we hope to have sufficient testable material. For the sake of research, I would like to ask all breeders who think they might have a foal with WFFS, to contact their veterinarian, so that a hair sample can be taken (pulled tail hair, not cut) and be examined. If desired, breeders can also contact the department of Internal Medicine of the Horse of the Faculty of Veterinary Medicine at Utrecht University directly.”

If my horse is WFFS carrier, does that also affect it’s health?

Sloet: "No, as far as we know, this is not the case. Carriers do not seem to have any advantages or disadvantages of the gene. Carriers can be excellent sport horses, who by chance have a deviation on one gene, while the accompanying second gene is good. They do not, as far as known, have any hindrance of this in day-to-day life."

What is the risk that my foal has WFFS?

Dr. ir. Ducro: "As far as is known now, the condition is determined by one gene. Stallion and mare must both be carriers of this abnormal gene, then 25% of the foals will have the condition WFFS, 50% will be carriers and 25% is 'free'. "

Is more known about similar disorders within breeding?

Ducro: "Yes, WFFS is similar in terms of inheritance to hydrocephalus and dwarfism in Friesians. Friesians are nowadays all being tested. Carriers can be used for breeding, but crossing of carriers is being avoided. Such hereditary defects also occur in cattle, and bulls that are carriers of a hereditary defect can also become breeding bulls. The bull gets a note that he is carrier of a disease and it is up to the farmer if he wants to use this bull in his breeding program."

Can I still use a stallion who is a WFFS carrier?

Ducro: "Yes, but it is important to combine these stallions with mares that are not carriers themselves. KWPN stallions are approved after a very strict selection and most of the time they are very talented horses from carefully selected damlines. It would be a shame if breeders would no longer use these stallions for breeding and the talents of these stallions would not be passed on. When a carrier is crossed with a non-carrier, this well never result to an affected foal, for which two carriers are required. However, crossing a carrier with a non-carrier gives a 50% chance of a carrier as a descendant, and a 50% chance of 'free' offspring. If the breeder wants to use the offspring of this cross for breeding, it is advisable to test whether this horse is a carrier or not. In this way optimal use is made of the availability of a DNA test to preserve the favorable characteristics of the stallion for the population."

Should I have my mare tested?

Knaap: "It is always advisable to test broodmares so that you know whether your mare is a carrier or not. Carriers can be used for breeding, but the crossing of carriers should be avoided. Testing to find out the carrier status is very simple. At the request of the KWPN, a test has recently become available in the Netherlands, at the Van Haeringen Laboratory in Wageningen. You can send a hair sample (with hair follicle) to the Laboratory and usually get the result within ten working days. The test costs 39.50 Euros excluding VAT. We are investigating the possibilities for facilitating this for the breeders. "

What should I do if my mare tests positive for WFFS?

Ducro: "If your mare is interesting for breeding, you can still use her, but always in combination with a WFFS free stallion." Like that, you never risk a sick foal. "The offspring from the cross between carrier and non-carrier have 50% chance of being a carrier and a 50% chance of being WFFS-free."

The KWPN already has hair samples from my horse: can the test be carried out with this sample?

Knaap: "At the time, these hair samples were collected when the foal was micro-chipped with a different purpose, and are often used for paternity testing and / or genomic selection. If enough hair is still available, it can be used for this purpose."

Will the KWPN test all approved stallions for WFFS?

Knaap: "Yes, all active KWPN approved stallions and the stallions in the current performance test will be tested ASAP. We publish the results on the KWPN website. The WFFS gene is not a selection criterion, but it is relevant information for the breeders to know a stallion’s status. "

What other steps will KWPN take?

Knaap: "The testing of horses is a logistically extensive project. In the context of the prioritization we proceed step by step. The KWPN has ensured that a test is available at the Van Haeringen Laboratory in the Netherlands, and has asked the WBFSH to put WFFS on the agenda. We have now started the large-scale testing of the KWPN approved stallions, this has now the highest priority. Then we will look with the breeding councils on how we can integrate the screening of mares in the breeding program and how to facilitate this for the breeders. In addition, we want to investigate the possibilities to integrate the WFFS test into existing tests the KWPN already conducts. As soon as more is known about this, we will announce this via IDS international and our website. "

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The KWPN (Studbook of the Royal Dutch Sport Horse) is a Netherlands-based organization specializing in the breeding of jumpers, dressage horses, harness horses, and Gelder horses.

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