A federal judge in Montana ruled that the plans to reopen the border to young Canadian cattle were to be postponed, though the length of the delay was not clear.
District Judge Richard Cebull granted the request for a preliminary injunction brought by a ranchers group that argued the reopening would expose their cattle - and US consumers to mad-cow disease. He also demanded that an agreement be made within 10 days for a hearing date on whether he should issue a permanent injunction against the plan for importing live animals.
Agriculture Secretary Mike Johanns said he was "very disappointed" in the ruling which would have re-established trade with Canada for live cattle under 30 months of age.
"The USDA remains confident that the requirements of the minimal-risk rule, in combination with the animal and public health measures already in place in the US and Canada, provide the utmost protection to consumers and livestock," said Johanns.
BSE remains a sensitive issue for consumers, policy makers and the beef industry. In late December 2003, the US identified a BSE infected cow in the state of Washington, leading to a ban from more than 20 countries on imports of US beef.
The after-effects are still being felt. A Wall Street Journal Online/Harris Interactive Health-Care Poll conducted last year in the US showed that one in every five American adults - 21 percent - said that fear of mad cow disease would change their eating habits, while 78 percent of these people said that they would eat less beef.
Some 16 percent indicated that they would stop eating beef altogether.
However, the agency remains confident in the safety of the US beef supply. It says that the current ban on specified risk materials from the human food chain provides protection to public health, should another case of BSE ever be detected.
Measures to strengthen public health safeguards in the US include the longstanding ban on imports of live cattle, other ruminants, and most ruminant products from high-risk countries. In addition, non-ambulatory cattle have been banned from the human food chain and air-injection stunning of cattle has been made illegal.
And any animal presented for slaughter that has been sampled for BSE, will be held until the test results have been confirmed negative.
The global beef industry's worst fear is a rerun of the BSE crisis that gripped the UK in the late 1990s. Domestic sales of beef products declined immediately by 40 per cent following reports of a possible link between BSE and new variant CJD - a human form of BSE - in 1996. Export markets were completely lost.