Washington ? Spying three intruders inside their grassy Loudoun County, Va., sanctuary, a herd of horned bovines immediately went on the defensive. They grouped together and charged full speed across the field to within 10 feet, dropped their front shoulders and dared anyone to take another step.

“That’s the yak in them,” farmer Pete Mentzer explained.

The what?

“They’re 50-50 yak and beef animal,” he said of the creatures, which have long faces, low-set ears, thick coats and tails, and oddly angled horns.

Mentzer, who grew up farming in Loudoun, and his partner, Jim Dumbrell, a retired British oil and gas pipeline consultant, are breeding yattle – a cross between cows and yaks. “We laughingly call it Frankensteer,” Dumbrell said of the crossbreed.

Right now, yattle are the next big nothing. But Mentzer and Dumbrell hope they become the rage of a health-conscious society looking for a low-fat alternative to traditional beef.

Because yaks, with their horns and long coats, are cold-weather animals native to such places as Tibet, their fat is concentrated on the outside of their bodies, not riddled throughout, resulting in a low-cholesterol but slightly tough meat, Dumbrell said. By breeding the animals with beef cattle, the pair hopes to meld the best traits of both species.

A far cry from the days when the success or failure of the year’s harvest governed family fortunes, ventures such as Dumbrell’s are often pursued more out of whimsy than necessity.

“I get a lot of pleasure out of it,” said Dumbrell, 65, who came to Loudoun 18 years ago and describes himself as a novice farmer. “I love working with animals.”

Dumbrell said he got the idea to raise livestock after taking in a “seriously deformed” cow called Stumpy that was being shunned by the rest of the herd on a neighbor’s farm. Seeking company for the creature, he explored his options.

“We were trying to find something that was different. We were thinking of alpacas, then bison, but the fencing for bison would be pretty expensive,” given their strength and aggression. He summed up his reasons for choosing yaks with a single word and a grin: “Stupidity.”

Realizing he’d need an actual farmer to help handle the up-to-1,300-pound animals, Dumbrell partnered with his neighbor, Mentzer, who, after 36 years of working for Pepco, decided he wanted to return to his roots and give farming another go.

Asked whether he ever thought he’d be partnered with a British yattle farmer, Mentzer, 69, said: “Absolutely not. No way, shape or form.”

Dumbrell has 30 yaks on his 70-acre Purcellville farm – which flies both British and American flags near its workshop – while cattle and yattle are kept on neighboring farms where Mentzer works as a manager.

Unlike other crosses such as mules, which are infertile, only male yattle are sterile, allowing females – which might or might not have horns – to procreate with bulls.

Yattle are not the first example of two species being crossed to please the human palate.

In the early 1970s, beefalo – crosses of bison and beef cattle – was marketed commercially in the United States. That venture has largely flopped because of a low supply of animals, said Bob Weaber, a geneticist specializing in beef cattle with the University of Missouri.