Researchers hunt for gene causing pony foal deaths

Scientists at the Animal Health Trust in Newmarket and the Liverpool Veterinary School have teamed up to find the cause of Fell pony syndrome (FPS). The research has been made possible by a grant from the Horse Trust.

Fell pony syndrome is always fatal. Affected foals die or are euthanased, usually before they reach three months of age. Ponies that reach weaning age are too old to have the disease - although they may still be carriers.

The condition affects the immune system. Foals are unable to respond adequately to infection. They die from infectious diseases that they cannot overcome.

Signs usually are first noticed when the foal is a few weeks old, and include loss of condition, diarrhoea, coughing and weight loss. As the condition progresses, the foal develops anaemia, immune dysfunction, and wasting. Foals succumb to opportunistic infections such as diarrhoea and pneumonia.

As well as in Britain, affected Fell pony foals have been identified in The Netherlands and the USA.

Analysis of the pedigrees of affected foals strongly suggests that the condition is caused by a single autosomal recessive genetic defect.

Every foal inherits half of its genes from each parent. If both parents carry the defective gene the resulting foal has a one in four chance of developing the condition. There is also a one in two chance of producing another carrier, and a one in four chance that the foal will be completely normal.

It is not known how many animals are carriers. Estimates suggest that 10-20% of the foals born each year are affected. If so, then probably between 60-90% of the breed carry the defective gene.

Numbers of Fell ponies declined dramatically after the Second World War. The small number of animals used for breeding gave ideal conditions for an inherited condition to be passed on to subsequent generations.

A DNA-based test for the defective gene would enable horses carrying the defect to be identified. By not breeding a carrier stallion with a carrier mare the conception of affected foals could be prevented.

Fell ponies have been crossed with other breeds and so the defective gene may also be present in other breeds as well. A test would allow the extent of the problem to be assessed, both in Fell ponies and also in other breeds that have been crossed with Fell ponies.

The project leader is Dr June Swinburn of the Animal Health Trust. "The success of this project will prevent the suffering of newborn Fell pony foals affected with FPS," she says.

"Foals affected by the condition inherit an incurable genetic defect, which results in severe wasting and a profound anaemia together with multiple infections. Veterinary intervention is in vain and once the condition is diagnosed foals are often euthanased.

"Breeders are supportive of our attempt to develop a diagnostic test, which will help to prevent carrier-carrier matings, one in four of which results in an affected foal."