The Big Roundup has become Big Business.

The dramatic rise in demand for horse meat - for human consumption in Europe and Japan and for pet use domestically - has triggered intense competition between buyers of both riding horses and "killers" at Midwest auctions.

The end result has been a boost in the price of an average - not quality - riding horse from $150 to a range between $400 and $800, while the price per pound of horse flesh has overtaken the average price per pound of a slaughter cow.

At a horse auction in Waverly, Iowa, last week, bids for the 1,000 animals on the block were "the highest I have ever heard of - $400 to $800," said Roy Simon of Lakeville, Minn., a horse breeder and major supplier of "killers" to meat exporters. "Killers" are the aged, infirm or ill-tempered horses that are "turned out" by their owners to feed for a few weeks on their way to the slaughter house.

Simon sells 300 to 400 horses a week to Jet Pack International of Blaine, Minn., and Seymour Pack of Milwaukee, Wis., two of the dozen horse meat exporters in the U.S. "We buy them primarily in Iowa, South Dakota and Minnesota," he said. The auctions are bigger now than they ever were and the buyers are coming from Canada, the East Coast - all over."

The horses being sought by the packing plants are healthy, not too old, not too thin and weighing between 1,000 and 1,500 pounds. A good price for a quality killer is 32 cents a pound, according to Karen Borklund at Jet Park International. Prime catle are priced at 36 to 37 cents a pound, while a good slaughter cow now ranges between 24 and 30 cents a pound, Simon said.

"It's crazy. Horses should be cheaper than cows," he said. "You'd have never have expected this a couple of years ago."

But in many parts of the world, horse meat has long been a delicacy, priced at a premium to beef. Horse meat butcher shops in Belgium and France are distinctly marked with the stuffed head of a horse at or outside the entrance, explained Fred Lege of the Agriculture Department's Foreign Agriculture Service's livestock division.

France, Belgium and Italy are the major markets for the frozen hindquarters packed in the Midwest, while the boned front quarters are sold to Japan, Borklund said. Agriculture Department livestock export statistics show a 9 per cent increase in specialty meats, which include horse meat, between January 1977 and January 1976.

"It's very high protein meat, very low fat, very lean," Lege said, "and some people think it has a better flavor than beef."

Lege disagreed that the demand for killers has had an effect on riding horse values.

"There's more and more competition for killers and the supply is very nearly stable," Lege said. "But the price of killers has nothing to do with the price of riding horses, which have indeed skyrocketed. Packing plant demand has just put a floor under the price of a killer, that's all."

Lege said distinct and separate demand for riding horses is the basis for higher saddle horse prices. "The people who always wanted to be Roy Rogers now have the money to buy," he said. "It's that simple."

Auction participants insisted, however, that the aggressiveness of packing plant buyers and suppliers have bid up values to unprecedented levels.

"Only 50 killers finally went at the Waverly auction," Simon said, "but the packers were bidding $300 to $400 for animals to slaughter, forcing up the saddle horse prices.

None of the suppliers, packers or livestock experts queried admitted to having tasted horse meat.

"Having raised horses all my life, I'd hate like hell to eat one," Lege said. "But there've been times when I've been angry enough at one of my horses to . . . . Then I'd have eaten it raw."