The U.S. Senate voted to overturn a Bush administration plan on Thursday to allow imports of Canadian cattle, the second defeat in two days for the administration’s efforts to normalize beef trade roiled by mad cow disease in North America.

Senators passed a so-called resolution of disagreement, voting 52-46, in the first step under a 1996 law to void the U.S. Agriculture Department regulation.

The White House said the president will veto the resolution if it is also passed by the House of Representatives and sent to him.

Canadian cattle and beef were cut off in May 2003 after Canada reported its first native case of the fatal bovine disease. Some beef imports resumed a few months later.

Since the USDA unveiled a plan in late December to reopen the border on March 7 to Canadian cattle shipments and more beef, the regulation has taken hits from all three branches of the U.S. government.

Last month, the USDA itself withdrew a significant portion of its own plan by dropping a provision to allow shipments of Canadian beef from older slaughtered cattle. USDA Secretary Mike Johanns took the action after spirited lobbying from American meatpackers.

On Wednesday, a federal judge in Montana put the entire USDA trade proposal on temporary hold in a lawsuit filed by some U.S. cattlemen.

USDA officials say renewed cattle trade with Canada would set a precedent for Japan and South Korea to end their bans on U.S. beef. American beef exports plummeted with the discovery of the first U.S. mad cow case in late 2003.

Sen. Kent Conrad, a North Dakota Democrat and lead sponsor of the resolution, said he was skeptical of Canada’s safeguards against the brain-wasting disease. People can contract a human version of the malady by eating infected foods.

“This runs a risk we should not take,” said Conrad. “This is profoundly a health issue.”

An estimated 1 million head of younger cattle would be shipped for U.S. slaughter under the USDA regulation and some senators praised the rule to resume some cattle imports.

“All of the sound science says the (USDA) has made the proper decision,” said Agriculture Committee chairman Saxby Chambliss, Georgia Republican.

Both the United States and Canada have similar rules requiring removal of brains, spinal columns, nervous tissue and other items deemed to pose the highest risk of the disease and banning the used of cattle parts in cattle feed.

While some senators questioned Canadian safeguards, others like Wyoming Republican Craig Thomas said U.S. beef exports to Asia should be rebuilt before Canadian cattle were allowed. Idaho Republican Larry Craig pointed to long-running trade disputes with Canada over timber and potatoes and said he had no sympathy for Canada, the largest U.S. trade partner.

Thirteen Republicans joined a majority of the 44 Democrats in the 100-member Senate to pass the resolution.