The mutation responsible for Warmblood Fragile Foal Syndrome occurs at a low frequency among sport horses and Thoroughbreds in Ireland, researchers report, although they did sound a note of caution.
Foals who inherit the recessive gene for the syndrome from both their parents will be born with the condition, which is characterized by abnormal collagen biosynthesis. They will be affected by abnormally fragile skin, joint hypermobility, and vessel and tissue fragility.
Newborn foals are euthanized shortly after birth because of the poor prognosis for the untreatable condition.
Áine Rowe and her fellow researchers at University College Dublin noted that while the mutation has been identified in non-Warmblood breeds, including the Thoroughbred, all cases reported so far in the scientific literature have been Warmblood foals.
The study team set out to investigate the carrier frequency of the mutation in the Thoroughbred and sport horse populations in Ireland.
A molecular-based test was developed at the university’s School of Veterinary Medicine, which was used to test hair samples from 469 horses representing six different breeds across Ireland.
Six of the 303 sport horses, representing 1.98% of that group, were identified as carriers of the mutated gene. Three of the 109 Thoroughbreds tested, representing 2.75% of the group tested, were also carriers.
The carrier horses all originated from different herds and from the east and west of the country. Seven of the nine horses were female, one was an intact male and one was a gelding. The ages of the carriers ranged from 3 to 10 years old.
The mutated gene was not identified in any of the Standardbreds, Cobs, Connemaras, or other pony breeds tested.
The researchers, writing in the Irish Veterinary Journal, said the frequency of the mutated gene in sport horses and Thoroughbreds in Ireland was low.
“The low frequency in the sport horse population is likely a reflection of traditional breeding, which is influenced by the Thoroughbred and Irish Draft horse lines,” they said.
“Given the low frequency of the Warmblood Fragile Foal Syndrome allele in horses in Ireland, and the apparent lack of clinical evidence of the condition, the current economic impact of the disorder on the Irish equine industry appears relatively low.
“However, the predominance of young carrier animals with breeding potential in this study could herald an increase in the prevalence of this condition in the national herd in future years, in particular if carrier males remain intact and are used for breeding.”
They said considerable economic losses are sustained by individual breeders in the event of the birth of an affected foal. Knowledge of the carrier status of sires and dams allows informed breeding decisions to be made while maintaining genetic diversity.
“Available genetic testing should be utilized with the goal of improving the health and welfare of horses and safeguarding the equine industry,” they said. “Veterinarians should be proactive in this area.”
“The reporting of suspected genetic disease and submission of DNA samples for testing will increase our knowledge about the disorder, which can then be translated into best practices for breeding, thus improving the overall health of the equine population.”
The study team comprised Rowe, Sharon Flanagan, Gerald Barry, Lisa Katz and Vivienne Duggan, all with the Veterinary Sciences Centre at University College Dublin; and Elizabeth Lane, with the Animal Health Division of the Department of Agriculture, Food and the Marine.
Rowe, Á., Flanagan, S., Barry, G. et al. Warmblood fragile foal syndrome causative single nucleotide polymorphism frequency in horses in Ireland. Ir Vet J 74, 27 (2021). https://doi.org/10.1186/s13620-021-00206-1