Since the closing of many countries to US beef exports in December 2003, the country had managed to recover access to 82 per cent of its former markets, originally worth about $3.9 billion.
But last week Japan again cut off US beef exports after the country's agriculture ministry said inspectors found banned cattle backbone material in three of 41 boxes in a shipment.
Japan, the largest market for US beef exports, had only resumed imports from the US last month after a ban was imposed in May 2003. The finding of banned cattle parts violated the bilateral agreement with the US meant to keep BSE out of Japan.
With the confirmation yesterday that Canada had found BSE in another cow, other foreign buyers will now be questioning whether the US has safe beef.
US and Canadian officials are trying to downplay the finding. The Canadian Food Inspection Agency (CFIA) said the discovery of BSE in a six-year-old cross-bred cow born and raised in Alberta was "not unexpected".
No part of the animal entered the human food or animal feed systems, the CFIA stated. The inspectors noted that the case was discovered though the country's national surveillance programme, which targets cattle at highest risk of being infected with BSE. The programme has tested more than 87,000 animals since Canada's first BSE case in 2003.
"This detection is consistent with a low level of disease and does not indicate an increased risk of BSE in Canada," the CFIA stated. "Based on the guidelines and certification recommendations of the World Organisation for Animal Health, this finding should not affect Canada's ability to export live animals, beef and beef products."
Meanwhile US agriculture secretary Mike Johanns said he anticipates no change in the status of beef or live cattle imports to the US from Canada due to the new case.
"I am confident in the safety of beef and in the safeguards we and our approved beef trading partners have in place to protect our food supply," he stated. "We will continue to adhere to international guidelines in our relationships with all trading partners, and my hope continues to be that we achieve a system of science-based global beef trade."
Japan, Korea and others prohibited imports of US beef and beef products following the detection in 2003 of BSE in a single cow of Canadian origin in Washington State.
Japan was the largest importer of US beef prior to 2003, buying up $1.4 billion worth of the meat a year.
The US this month also reported reaching agreement with South Korea to resume exports later this year. Korea was the US' third largest market for beef exports.
In 2003, before the ban took effect, the US exported $815 million worth of beef and beef products to Korea, of which $449 million was boneless beef.
Thailand, China, Taiwan and Singapore still have bans on US beef.
A study released last April by the Kansas Agriculture Department estimates the industry lost up to $4.7 billion last year because of the mad cow case in Washington.
Scientists believe eating the BSE infected beef is the cause of the human variant, Creutzfeldt-Jakob disease, a fatal brain disorder that led to the death of about 150 people, mostly in the UK in the 1990s.