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Screen test for fragile skin

02.08.2007

White Dorper breeders and owners are hoping to eradicate a genetic disorder causing a lethal fragile skin condition among some of their drought-hardy flocks.

The disease dermatosparaxis also exists in other breeds but White Dorper breeders are the first to opt for a mass flock screening program in Australia.

"Their early adoption of a newly developed test should ensure this disease is effectively managed," NSW DPI research scientist, Dr Tracey Berg, said.

Dermatosparaxis is an inherited connective tissue disorder attributable to abnormal collagen in the skin which causes extreme skin fragility. Normal collagen provides elasticity and strength.

Dermatosparaxis most often affects lambs. They suffer tearing of the skin, usually in their inner thighs and under armpits. The severity of the condition results in death or euthanasia.

Attempts to stitch the skin usually fall apart, exacerbated when animals are handled to check the repair. Mild forms of the disease have been seen in adult sheep.

"If unchecked now, there could be a potential problem for the sheep industry in the future," Angus McTaggart, federal board president of the Dorper Sheep Breeders Society of Australia, said.

The disease has been reported elsewhere in Merino, South African White Dorper and Border Leicester-Southdown sheep.

Similar conditions occur in cattle, cats and humans (Ehlers- Danlos Syndrome type VIIC).

After Brendon O’Rourke and Dr Berg confirmed and defined the disorder in Australian White Dorper flocks at the Elizabeth Macarthur Agricultural Institute (EMAI) at Camden in 2006, they then developed a DNA test to screen individual sheep for the defective gene.

They developed the test in mid-2006 at the request of breeder Malcolm Green with subsequent support from the Breeders’ Society.

"The mutation exists in sheep from most of the Australian flocks we’ve tested," Dr Berg said.

Technical assistant Nelson Jimenez selects White Dorper hairs for analysis in the Regional Veterinary Laboratory at Camden. "Of the substantial number of sheep tested, 20 per cent were carriers.

"We have also received overseas submissions and detected carriers from several countries, so it is a world wide problem."

Dr Berg and her colleagues at EMAI are consequently recommending screening of all breeding stock, or at the very minimum, screening of all sires.

"The latter is the first step in managing both damage to reputations and economic loss," former head of the Regional Veterinary Laboratory at EMAI, Dr Keith Walker, said.

"The DNA test provides an avenue for genetically smarter breeding programs."

The breed society is taking advantage of reduced rate testing by being responsible for administering samples, invoicing and reporting results.

It will also note all results on its stud book registration records, to enable public scrutiny of both positive and negative pedigree discrimination by all breeders.

A number of cattle breed societies have embraced this approach, to reduce the incidence of genetic disorders. The new genetic test is available commercially from the Genetics laboratory at EMAI.

Contact Dr Rod Reece, Camden, (02) 4640 6309, for veterinary advice about the disease, or Ian Marsh, (02) 4640 6502, about testing.