Livestock scientists have created the world's first horse that was deliberately selected prior to conception to be born female.

Unlike Dolly the sheep and last month's 50 identical lab mice, the week-old filly, named Call Me Madam, is not a clone. It has a genetically different mother and father.Researchers say the reproductive method known as sperm sorting could fine-tune livestock herds, reducing the slaughter of millions of newborn animals by commercial operators because they turn out to be the wrong gender and have little market value.

The same lab method eventually might help save endangered species, they said

Sperm sorting previously has been successful in limited trials using cattle and pigs, but it has not yet been commercialized. Observers said horses are reproductively more difficult, and the method would be a breakthrough if it can be repeated.

"It could have a significant impact on agriculture," said biologist Ken White of Utah State University. "But it's not an automatic assumption that you can apply it to all species."

However, the Colorado-based consortium that developed the designer horse said they would not extend their reach beyond the barnyard to include human reproductive medicine and the creation of "designer babies."

"Some people are threatened by what they've been hearing, said Mervyn Jacobson of XY, the joint commercial venture with Colorado State University that bred the designer horse.

"Sperm sorting is good for the industry and good for the animals," Jacobson said. "Either you leave it to fate, or you can plan ahead in a way that makes economic sense and minimizes the trauma to the animals."

Federal agriculture researchers originally developed a laboratory method to separate sperm by gender. Sperm samples from various livestock species were highlighted under magnification to spot genetic differences.

The Y-chromosome sperm that would produce males when matched with an egg were separated from the X-chromosome sperm that would produce females. The process had to be streamlined to be commercially viable.

In nature, a stallion must deliver at least 500 million sperm to impregnate a mare. In Call Me Madam's case, the researchers sorted 150,000 of the X-chromosome sperm and surgically delivered them into the mare's reproductive tract. They still had to wait the normal 11-month gestation to see if their method worked.

Scientists said improving breeding efficiencies would reduce the number of unwanted animals. The dairy industry kills as many as 10 million unwanted male calves per year, they said.

Among horse breeders, polo stables prefer quicker-learning females. Muscular males make better show jumpers.

The firm is meeting with international conservation groups to identify an endangered mammal species that could expand its population if sperm sorting enabled it to produce more females.

Pandas in China and koalas in Australia already have received laboratory boosts with artificial insemination. But the gender outcomes - male or female - remained nature's prerogative.