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Rare Breeds Survival Trust Fell Foal Syndrome Symposium

Penrith Rugby Club, UK
by Mary Jean Gould-Earley, MD

On August 7, 2002, the Rare Breeds Survival Trust sponsored an informative symposium on the Fell Foal Syndrome. Speakers included Paul May, a local Veterinary Surgeon; Prof. Stuart Carter and Gareth Thomas (Veterinary Surgeon), both Syndrome Researchers from Liverpool University; Dr. Saffron Townsend, Technical Advisor for RBST; Dr. June Swinburne and Dr. Matthew Binns; Geneticists from Animal Health Trust; Miss Rosemary Masbridge, Chief Executive RBST, and Fell pony breeders Mrs. Carole Morland and Mrs. Jane Glass. Each of the speakers reviewed various facets of the syndrome including clinical signs, status of research, genetics, and breeders' perspectives on the problem. It was a very worthwhile meeting to say the least!

The following is a brief synopsis of the presentation:

• "Fell Foal Syndrome" is comprised of immunodeficiency and anemia which has been documented only in Fell pony foals. It results in repeated infections as well as progressive and profound anemia, invariably resulting in death by 3-4 months of age. There is no known cure for this disease.
• The Syndrome is presumed to be caused by a lethal recessive gene. This remains unproven but researchers feel very strongly this is the case.
• The cause remains unknown but foals with the syndrome have been found to have reduced number of B-lymphocytes, the type of white blood cell which is responsible for the production of antibodies. (This is the basis of the current blood test used for diagnosis.) Antibodies are necessary weapons of the immune system needed to fight against infection.
• Affected foals usually appear normal at birth but at about 4-6 weeks of age begin to deteriorate, usually dying by 3-4 months of age (if not euthanized before then). Foals that show no signs of the syndrome by 4 months of age areno longer considered to be at risk.
• The timing of onset of the syndrome is believed related to antibody production. Foals normally receive colostrum from their mothers at birth which is rich in antibodies. The foals' immune systems need to take over antibody production as these antibodies from their mothers wear off, usually around 4-8 weeks of age. Failure to do so results in impaired immunity and susceptibility to infections.
• In the last few years, on average there have been approximately 10/250 syndrome foals documented each year in the UK.
• If the disease is indeed inherited as a recessive gene, based on the incidence of the syndrome, it is currently believed that 1/3 to 1/2 of Fell ponies are carriers of this presumed lethal gene. This is only an estimate and until it is confirmed recessive and a carrier test is developed the true prevalence of the suspected gene is unknown.
• If it is a recessive disease, (barring mutation) breeding a carrier to a non-carrier will never produce a syndrome foal. Breeding a carrier to a carrier will produce 50% carriers, 25% non-carriers, and 25% syndrome foals. A carrier test may thus be helpful.
• RBST and Syndrome researchers STRONGLY advise that no attempt should be made to breed out this disease on the basis of rumors and hearsay. To attempt to do so, particularly without a carrier test, may do far more damage to the breed by unnecessarily restricting an already-too-narrow gene pool. Without a carrier test, breeding programs should NOT be altered because of the syndrome.
• Because of the small gene pool and relatively small global population of Fell ponies, even if a carrier test is developed, carrier animals should not be eliminated from the gene pool. Doing so may cause further damage to the breed by restricting a narrow gene pool, potentially exposing other deleterious recessive traits and/or favoring otherwise lesser-quality, non-carrier animals to be used for breeding.
• Because of the small global population of Fell ponies in addition to the possibility of a lethal recessive gene, RBST has changed the Fell pony classification from "Rare" to "Endangered". Preserving the Fell pony breed thus requires the concerted effort of all Fell pony breeders! Continued research requires the cooperation of all breeders, particularly those with affected foals since all such data is needed to facilitate the research progress.

Compared to the previous presentation on the Syndrome by Gareth Thomas in September, 2000, a few changes have occurred. (See notes from prior presentation at Fell Foal Syndrome - Research Progress Report). This includes the estimate of carriers which was previously believed to be at "saturation" (i.e., 2/3). It is now estimated at 1/3 to 1/2. Of course that is still a very significant amount in a very small population!! The estimate assumes that the syndrome is recessive and also that the incidence of syndrome foals produced is not skewed by avoiding suspected carrier stallions in favor of non-carriers. Another change is that the syndrome can now be diagnosed with a blood test in the appropriate clinical setting, whereas previously it required bone marrow and/or lymph node biopsy. In addition, reduced B-lymphocyte number is now apparent. These may be abnormal even before the profound anemia develops.

(This article was kindly proofread by Gareth Thomas BVM&S MRCVS)

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