Canadian officials said Tuesday that they had found a new case of mad cow disease, a report made more worrisome because the cow was born after feed restrictions intended to prevent the spread of the disease were put in place in 1997.

It was the second infected cow from the western province of Alberta found in the two weeks since the Bush administration announced that it would soon allow imports of young Canadian cattle, for the first time since the initial case was found in May 2003. But in the other recent case, the cow was nearly 8 years old, born before the feed restrictions.

The new case is likely to strengthen a legal challenge to the administration's decision, which as of March 7 would allow the import of cows under the age of 30 months as well as of an expanded variety of beef. The challenge, filed Monday by a group of Montana ranchers, said the import of Canadian livestock would endanger public health and American cattle.