Washington ? A livestock tracking system planned by the government will not include the age of animals, despite the key role age has played in mad cow disease investigations.

Agriculture Department officials say they don’t want to overburden ranchers and can track most birth dates. Critics said the omission could make the system worthless.

“So what’s the point of having this animal ID system? This is one fact you actually really need to know when it comes to mad cow,” Jean Halloran, director of food policy initiatives at Consumers Union, said Monday.

The department promised to create the system after the nation’s first case of mad cow disease two years ago and has already spent $84 million on it. Earlier this month, Agriculture Secretary Mike Johanns promised it would be in place by 2009.

“When you’re dealing with contagious diseases such as foot-and-mouth disease or exotic Newcastle, age really isn’t all that important,” department spokeswoman Dore Mobley said. “It’s important when you’re talking about BSE to estimate when an animal may have become infected.”

The goal is to allow authorities, within 48 hours after a disease is discovered, to pinpoint a single animal’s movements. Industry groups are collecting and keeping the data, which the government intends to tap when there is an outbreak.

Mad cow disease doesn’t spread like the flu; scientists say it spreads only when cattle eat feed containing diseased cattle tissue. Ground-up cattle remains were once commonly added to feed as protein, but the government essentially halted the practice nine years ago.

The age of infected cattle may indicate whether the safeguard is working. So far, infected cattle in the U.S. appear to have been born before the feed restrictions took effect.

The nation’s dominant cattle producer group agrees: The National Cattlemen’s Beef Assn. helped create a livestock tracking system that includes animal ages.

“Should they be asking for it? Probably,” Jay Truitt, a lobbyist for the group, said of the Agriculture Department. “So we’ve quit trying to figure out what they’re looking for and just tried to build a system that is really meeting the marketplace expectations right now, and date of birth is one of those factors.”