The U.S. Department of Agriculture had planned to reopen the border beginning Monday.
But following arguments from livestock interests that the government's plan was premature, U.S. District Judge Richard Cebull granted a temporary court order preventing it from going into effect.
United Stockgrowers of America sued the U.S. Department of Agriculture in January, seeking to block Canadian cattle and beef imports. The Billings-based ranchers' group contends the USDA plan would pose a risk to both consumers and U.S. cattle producers.
The cattle organization had asked the judge to keep the USDA from implementing the plan until the lawsuit is heard. Cebull ordered attorneys for both sides to prepare for a trial in that case.
The group's attorney, Cliff Edwards, told Cebull in court Wednesday it would be "insane" to allow the import of cattle from a country that has already reported two new cases of mad cow disease, or bovine spongiform encephalopathy, this year.
An attorney for the government, Lisa Olson, argued that the plan was as safe as it possibly could be.
Last month, Canadian authorities confirmed another case of mad cow disease in the western province of Alberta - the second animal found to have the deadly brain-wasting disease in Canada since U.S. officials announced in December they would resume the cross-border cattle trade in March.
Canadian officials said no part of the cow - the third case of the disease ever found in Canada - has entered the human or animal feed system.
Ron DeHaven, administrator of the Agriculture Department's Animal and Plant Health Inspection Service, said in January the agency was confident that protections in place in Canada and the United States would safeguard U.S. consumers and livestock.
The latest case of bovine spongiform encephalopathy (BSE) was discovered in an animal under 7 years old. Canadian Agriculture Minister Andy Mitchell said the case was unrelated to the second case of the disease, which was confirmed Jan. 2 and also involved an Alberta cow.
"A third case of BSE in a cow in Canada has been confirmed today through our surveillance system," Mitchell said in a news conference in Ottawa, the nation's capital. "This is not unexpected, as we have already acknowledged that there is a low level of incidence of BSE in North America."
The latest sick cow was born after a 1997 feed ban in Canada removed the use of animal remains in feed, commonly believed to be the cause of the disease. This makes this third Canadian cow with BSE more serious than the others because the cause could be much more difficult to trace.
However, Dr. Brian Evans of the Canadian Food Inspection Agency said the cow was most likely exposed to feed before the ban came into effect in the fall of 1997 and that his agency was investigating.
Nevertheless, Mitchell stressed the new case was not a cause for alarm.
Under World Health Organization guidelines, a country may have up to 11 cases of mad cow disease in a year and still be considered a minimal-risk country.
It appeared in Britain in 1986 and spread through Europe and Asia, prompting massive destruction of herds and devastating the European beef industry. So far 147 people in Britain, and another 10 elsewhere, are known to have contracted Creutzfeldt-Jakob disease since BSE was first identified.