BILLINGS, Mont. - Confirmation of a new case of mad cow disease in Canada on Monday prompted calls by some U.S. cattle industry groups to halt cattle and beef trade, until how the cow became infected is better understood. The U.S. secretary of agriculture said suspension of trade is unlikely.

The case, however, could affect whether the government proposes expanding such trade with Canada.

Canadian authorities on Monday confirmed that country's fourth case of mad cow disease since May 2003 - in a cow in Alberta. They said the animal, about 6 years old, reached neither the chain of food for humans nor animal feed systems.

U.S. Agriculture Secretary Mike Johanns, in a statement, said he anticipated no change in trade status, based on information provided by Canada's agriculture minister. But he said agency officials would monitor the situation and work with Canadian investigators.

The United States allows imports of Canadian beef and cattle under 30 months of age, with restrictions, U.S. Department of Agriculture spokesman Ed Loyd said.

Still, some industry groups, such as the National Farmers Union, urged the suspension of beef and cattle trade until more answers about the case emerge. One concern is that the cow was born after Canada, in 1997, banned use of cattle protein in cattle feed. Mad cow disease, formally known as bovine spongiform encephalopathy, or BSE, is believed to spread through feed with certain tissues from infected animals.

''This confirms some of the concerns we had all along, that they have a more severe problem in Canada than the U.S.,'' said Jim Magagna, of the Wyoming Stock Growers Association.

The Canadian Cattlemen's Association and several U.S. industry trade groups, two of them representing meat packers, said the new mad cow case was not unexpected and points to the effectiveness of the safeguards and surveillance system in place.