Outback sheep are slaughtered by the thousand as the world's longest fence falls into disrepair

Paul and Christine Ryan were prepared for many challenges, including isolation and drought, when they moved to the remote Nullarbor Plain in Western Australia to farm sheep. What they did not expect was to see 2,000 of their animals slaughtered by wild dogs within two years.

Across Australia, farmers are losing an unprecedented number of animals to packs of dogs roaming the Outback. The dogs, which can fell a full-grown kangaroo and maul sheep for fun, are so plentiful that a bounty - A$20 (£8) per head - has been introduced in one district to encourage people to kill them.

The scourge is blamed on the abandonment of long-standing measures to control both dingoes - primitive dogs introduced by Asian seafarers 4,000 years ago - and dingo-domestic dog hybrids.

The Dog Fence, a 3,500-mile barrier built across the continent to keep dingoes out of sheep farming country, is poorly maintained in some areas. Many of the professional doggers, once employed by state governments to trap wild dogs, have been dismissed to cut costs.

Patrolling farms where the average paddock covers five square miles is not an easy task. The Ryans find mutilated sheep carcasses on their 500,000-acre property, Fraser Range, near Balladonia, with depressing regularity.

"It's a massacre," said Mrs Ryan. "The sheep have got no hope. I've seen a dog grab a sheep and chew it, rip its skin off. It's not for food; it's just pure sport."

But with the dingo classified as a native species and protected in some regions, the issue of controlling the population is controversial. Some farmers say that cross-breeds, often larger and more aggressive than dingoes, are a greater threat. They have little fear of humans and roam close to homesteads on sprawling Outback properties.

Colin Nicholl, the president of the Western Australia Farmers Federation, said wild dog numbers had swollen because excessive reliance had been placed on aerial baiting with poison. But even trapping was not always effective. "The dogs have been known to chew a foot off to escape from a trap and run on three legs afterwards," he said.

Some farmers have lost 200 sheep overnight to wild dogs, and many have switched to cattle, he said. "But now the dogs are starting to attack young calves for the first time."

The Dog Fence stretches from South Australia to central Queensland. Farmers struggle to maintain it against the ravages of kangaroos and emus. Another monumental barrier, the Rabbit Proof Fence in Western Australia, has fallen into disrepair. It proved ineffective against rabbits but has kept out dingoes.

James Ferguson, a neighbour of the Ryans, has lost 20 per cent of his merino lambs.

"The problem is worse than it ever has been," he said. "There are probably more dogs now than before white settlement. We're losing sheep every day, and whenever you kill a dog, within days another takes its place."

Mr Ferguson, who runs up to 40,000 sheep on nearly 2 million acres, called for tougher controls. "The dogs are a pest, pure and simple," he said. "They're vicious killers, a threat not just to livestock but to the diversity of native wildlife.

"Six months ago I saw a cross-breed that clearly had alsatian in it. We're breeding our own wolf, given enough time."