YAKIMA – Beginning Monday, the United States will allow cattle over 30 months of age into the country from Canada, the latest step in a long disruption of trade caused by the discovery of mad cow disease there in 2003.

No one expects an immediate increase in cattle shipments across the border. At the same time, no one knows for sure how the decision will affect domestic ranchers or foreign markets, which have yet to fully recover from the discovery of an infected cow south of the border that same year.

One cattlemen’s group didn’t wait to find out, filing an emergency request Friday for a temporary restraining order to block the rule from taking effect.

In May 2003, the United States closed the border to cattle imports from Canada after an Alberta cow was confirmed with mad cow disease.

The border between the world’s largest trade partners reopened for Canadian beef from younger cattle within months of the original ban, and live cattle under the age of 30 months have been allowed to move across the border since July 2005.

But the border has remained closed to older cattle until the U.S. Department of Agriculture announced earlier this year that it would reopen Nov. 19 to cattle born after March 1, 1999. Agriculture officials have said the change is based in science and ensures that U.S. regulators will protect against the disease.

Critics counter that the federal government has failed to fully investigate the potential impact to U.S. ranchers.