7 April 2000

Sheep disease concerns…

By James Garner

BREEDERS are under-reporting a genetic disease in pedigree sheep flocks because they are concerned about losing income by declaring the problem.

The disease, called Dandy-Walker malformation, is most often found in Suffolk sheep, and despite causing concern within the breed, experts say it is being under-reported in pedigree flocks.

This is because Suffolk breeders whose flocks are infected with the genetic disease are concerned about losing breeding sales by declaring a problem, says vet Phil Scott from the Royal Dick School of Veterinary Studies, Edinburgh, in a report for UK Vet.

Its clinical symptoms cause foetuss heads to swell in the uterus, causing a grossly domed foetal head. This subsequently causes lambing difficulties, sometimes requiring a caesarian section.

According to genetic researchers at the University of Liverpool, which is conducting a study into the disease, Dandy-Walker appears to express a genetic link. "Preliminary investigations suggest that it could be a single recessive gene that is responsible, but this has not been formally shown," says molecular geneticist Stephen Kemp.

Despite causing some lamb losses in pedigree flocks – occasionally as high as 40% – Mr Scott says there is no reason to suggest the disease will be transferred to commercial lowland flocks. "It seems unique to Suffolks. I have never seen it found in a cross-bred flock."

This is disputed by Prof Kemp, who says there is no evidence that Dandy-Walker should be breed specific and that Suffolks are more susceptible to it. He also disagrees that commercial flocks cant be infected.

His interpretation suggests that closed commercial flocks breeding their own replacements may see cases. If a ram carrying the gene was used repeatedly in a commercial flock and some progeny carrying the recessive gene were also brought into that flock as replacements, then cases would be seen, he says.

Prof Kemp says the diseases incidence within a flock increases with inbreeding. "If a carrier ram is used on his own daughters, then 25% of offspring will suffer and 50% will be carriers. If the ram is used again on these new progeny, then incidence becomes higher still."

Dandy-Walker is also difficult to treat, says Mr Scott. Once diagnosed, producers have two options: Either perform a caesarean operation or crush the lambs skull manually and deliver the lamb.

"I feel sorry for the ewe, its not fair on lambs or ewes and I have little sympathy for farmers who continue to breed from these sheep," says Mr Scott.

He reports an incident where he had given a producer advice that a ram and his progeny should not be used for further breeding purposes, but this was ignored because the producer had purchased the ram for £12,000 and needed to recoup some of his investment.

However, the problem looks likely to rumble on in pedigree Suffolk sheep, says Mr Scott. "The risks of financial losses are just too high for individual breeders. Once a flock declares a problem thats the end of its pedigree sales."

A statement from the Suffolk Sheep society refutes Mr Scotts claims. "As a breed society we are aware of Dandy-Walker malformation, but not at levels which cause concern," says chairman of council Jim Fleming.

"We pride ourselves in having kept ahead with all available health and genetic improvement schemes, but Dandy-Walker malformation is not one which has been to the fore."

DANDY-WALKER

&#8226 Foetuses born with domed heads.

&#8226 Genetic disorder?

&#8226 Breeders could lose sales.