New federal rules will be developed but the officials said they would apply only to animals being moved in interstate commerce, such as cattle raised in one state being transported to a slaughterhouse in another state.

It could take two years or more to create new federal rules, the officials said, and it was not clear how far the government would go to restrict the movement of livestock between states if the animals did not meet basic traceability standards.

The system was created by the Bush administration in 2004 after the discovery in late 2003 of a cow infected with mad cow disease.

Participation of ranchers and farmers in the identification system was voluntary, but the goal was to give every animal, or in the case of pigs and poultry, groups of animals, a unique identification number that would be entered in a database. The movements of animals would be tracked, and if there was a disease outbreak or a sick animal was found, officials could quickly locate other animals that had been exposed.

But the system quickly drew the ire of many farmers and ranchers, particularly cattle producers. Some objected to the cost of identification equipment and the extra work in having to report their animals’ movements. Others said they believed the voluntary system would become mandatory, that it was intrusive and that the federal government would use it to pry into their lives and finances.