SCIENCE: Desperately Seeking Dolly ; with the Consumption of Livestock Products Set to Double in the Next Decade, Worms Are Threatening to Decimate the World's Sheep Flocks. So Scientists Have Gone Prospecting for a Solution in East Africa. by Fred Pearce

Article excerpt

The Masai sheep herders of East Africa don't know it yet, but they are sitting on a genetic gold mine of benefit to farmers from Romney Marsh to Tasmania, the Welsh hills to the Falkland Islands. Their distinctive pure-bred sheep covered in red hair, a familiar site in the Rift Valley of Kenya, may soon prove to be the most valued rare breed of farm animals in the world.

The "red Masai" sheep, one of the forgotten flocks of Africa, have an unrivalled resistance to the biggest scourge of sheep - the billion-dollar problem of intestinal worms. And geneticists in Kenya believe their resistance lies in a handful of genes that could be transferred into other flocks worldwide. British veterinary scientists are watching their work with anticipation. So should hard- pressed British sheep farmers.

And their story has a wider importance. The red Masai are a potent example of the hidden genetic value locked up in obscure animal breeds round the world, a "barnyard biodiversity" of growing importance as modern methods of fighting animal diseases falter. Saving them will help feed as well as clothe the world.

For 40 years, farmers in rich countries have fought sheep worms with drugs. But, says Leyden Baker of the Nairobi-based International Livestock Research Institute (ILRI), "the resistance of worms to the drugs is growing. We could soon be losing 30 or 40 per cent of wool and meat production because of premature deaths and sickness."

The drugs are the internal counterpart to chemical sheep dip, which attacks infestations in sheep fleece. And, like sheep dip, there are also growing environmental and health concerns because the drugs tend to build up in meat and pastures. For such reasons, ILRI has spent a decade searching for an alternative to the drugs by scouring Africa for native breeds of sheep that show the strongest genetic resistance to the worms. Two years ago, they settled on the red Masai.

"It is a remarkable animal," says Michael Stear of Glasgow University's veterinary school. "The red Masai thrives in conditions that would kill many other sheep breeds." In particular, it shrugs off a virulent African worm called Haemonchus contortus that sucks blood from the gut, leaving other sheep sick and anaemic.

Despite its unique attribute, there hasn't been a rush to add the Masai sheep to flocks round the world because of an equally obvious disadvantage. They grow hair and not wool. So the holy grail is to find the gene or genes that give resistance.

Two years ago, Baker and his team starting buying pure-bred red Masai from markets in the Rift Valley. It took six months to buy 400. Today, more than 1,000 sheep containing varying amounts of red Masai genes graze in the paddocks at ILRI. Baker has crossbred them with South African Dorper sheep that grow white wool in an African climate, but have an especially low resistance to worms.

By juggling the breeding over several generations, tracking which offspring become resistant and which do not, and then analysing their genetic makeup, Baker hopes to pinpoint the genes in the red Masai sheep that control resistance. "By the middle of next year we should be ready to begin the analysis. Within two years we should have preliminary results," he says.

And it could be a lot sooner than that. To speed up the process, ILRI is collaborating with Derek Wakelin at the University of Nottingham to screen mice in the hope of identifying those parts of the mouse genetic makeup that carry genes for resistance to the worms. "We don't know yet if the same genes would do the job in sheep as in mice. But we could get lucky. And the great thing about mice is that you can get results much more quickly," says Baker.

If his luck is in, he could by the end of the year have a hotline to the important sheep genes. He may also be able to draw on help from Europe, where Michael Stear has isolated a couple of genes that give Scottish Blackfaced sheep some resistance to British worms. …