Crossing anything human with four-legged hoofers evokes images of mythical half-man, half-animal centaurs from ancient Greece.

In reality, genetically altered goats look and behave no differently from regular ones - both are just as eager to gnaw Murray`s sleeves and untie his shoes at the goat barn.

"Could you get your grubby paws off?" the University of California-Davis professor asked of his inquisitive test subjects during a recent tour.

Murray and fellow animal scientist Elizabeth Maga engineered a small herd of Alpine and Toggenburg dairy goats to produce high levels of a human antibiotic-like protein in their milk.

Just as mother`s milk helps protect infants from germs, the researchers figured, humanized goat`s or cow`s milk would better defend dairy animals and their offspring from illness. Germ-fighting milk might also slow spoilage, prolonging the shelf life of dairy products.

The scientists` ultimate question, though, is a humanitarian one:

Could the same procedure produce fortified powdered milk and, eventually, genetically modified goat herds for poor regions of the world?

The beneficial protein, lysozyme, destroys bacteria that cause intestinal infections and diarrhea, which every year claim more than 2 million impoverished young lives. That`s a toll among children under age 5 higher than from AIDS, tuberculosis and malaria combined, according to the World Health Organization.

"If we can prevent some of that, I think we should do it," Murray said, mindful of long-standing protests from animal-rights activists, ethical concerns and fears of messing with Mother Nature.

The goat`s milk represents one of the first genetically engineered food products designed to improve human health, though none has been approved for human consumption.

Scientists have been manipulating animal genes for nearly 25 years. They`ve changed properties of milk for human food and as raw material for pharmaceuticals - turning animals into virtual medicine factories. Murray himself has changed the genes of cows, sheep, pigs and mice.

The goat`s-milk experiments, however, are among the few to transfer human genes to animals, said Michael Fernandez, former director of the Pew Initiative on Food and Biotechnology.

"It`s certainly not the predominant practice right now," Fernandez said. Private biotechnology companies and universities usually obtain genetic material from microbes or plants, not humans, he said.

Doug Gurian-Sherman, a biotechnology specialist with the Union of Concerned Scientists advocacy group, said he has concerns about transgenic goats.

Should the goats get into the wild - their altered genes indeed make them more fit to survive - they could more easily multiply and over-browse a landscape, threatening native species and causing erosion, he said.

"We don`t have a regulatory system that addresses these kind of environmental issues in this country, let alone developing countries," Gurian-Sherman said.

Why human genes for goats?

Goats, humans and all other mammals have lysozyme in milk, saliva and tears. Human breast milk, however, carries at least 1,600 times more than goat`s milk.

UC-Davis dairy goats born with the human gene that regulates lysozyme in mammary glands have far more lysozyme in their milk than they would naturally - 67 percent of human levels compared with 0.06 percent, Murray said.

While other animals carry high levels of the protein, Davis researchers chose to inject the human gene to minimize chances of an allergic reaction, should people ever drink the modified goat`s milk.

"You drink lysozyme every day in your saliva, so the chances of you reacting to it are pretty small," said Maga, a research biologist in the animal-science department.

Several more studies are needed to satisfy food-safety regulators in the United States and elsewhere that this medicinal milk would be safe to drink, researchers said.

The latest findings, published in the May issue of the Journal of Nutrition, show altered goat`s milk helps fend off common E. coli-related illnesses in pigs, which have human-like digestive systems.

© 2008 The E.W. Scripps Co.