Japan, which used to be the largest export market for U.S. beef before the 2003 mad cow scare halted imports, is reportedly reviewing the safety of American beef in an effort to break down trade barriers.

Currently, Japan only accepts U.S. beef from cattle aged 20 months or younger because older cattle are thought to be at higher risk for mad cow, or bovine spongiform encephalopathy.  According to the National Cattlemen’s Beef Association, the restriction costs companies like Tyson Foods Inc.  and Cargill Inc. about $1 billion in sales annually.

From 2003 to 2005, Japan banned U.S. beef entirely after a case of mad cow was discovered in Washington state.  The country relaxed restrictions in late 2005, implementing the age cut off and also requiring that brains, vertebrate, spinal cord, and bone marrow be properly removed before export.

If Japan’s Food Safety Commission concludes that beef from older cattle is safe, it could help restore U.S. beef exports to pre-ban levels.

Susumu Harada, the U.S. Meat Export Federation’s senior director in Tokyo, told Bloomberg: “The change would remove obstacles in the beef trade as U.S. products for overseas shipments are mostly from cattle aged up to 24 months.”

Industry groups and some lawmakers say that Japan’s restrictions are not based on sound science and are inconsistent with international guidelines.

“At the very least, Japan should agree to immediately relax its age restrictions to 30 months as an interim step on a pathway that would amend its import protocol to be consistent with [World Organization for Animal health] guidelines,” a group of senators wrote to in a recent letter  to President Obama.

“The United States has spent years putting in place an effective system of interlocking safeguards that has led to the virtual elimination of BSE in our country,” reads the letter. “Because of these efforts, the U.S. has been classified as a controlled risk country by the World Organization for Animal Health (OIE), which indicates that U.S. beef products are completely safe for export and consumption.”

Officials from Japan and the U.S. continue to work on the issue, though when and if Japan will relax current restrictions remains unclear.