After exhuming the Alabama cow with mad cow disease, the government has concluded she was at least 10 years old and could have been infected before steps were taken to safeguard cattle feed, the Agriculture Department said Thursday.

Nine years ago, the United States banned ground-up cattle remains from use in cattle feed. Meat and bone meal from cattle was a common ingredient until it was implicated in a massive mad cow outbreak in the United Kingdom in the 1980s and 1990s. The disease was blamed for the deaths of 180,000 cattle and more than 150 people.

Experts checked the Alabama cow's teeth and determined she was 10 or older, the department said Thursday evening. That was the estimate of a local veterinarian.

Earlier Thursday, an official said the age is an approximation.

"After 5 years old, it is an approximation, but a fairly good approximation, in terms of looking at the amount of wear on the teeth, are there teeth missing, that kind of thing," said Ron DeHaven, administrator of the Agriculture Department's Animal and Plant Health Inspection Service.

"We'll have a number of people who are familiar with aging cattle by their dentition look at this animal and see if they concur with the original veterinarian," DeHaven said.

Despite the ban on cattle remains in feed, potential pathways for infection remain. Among them is restaurant plate waste, including meat and bones, that can be added to cattle feed. Many companies, including McDonald's, are pushing to close the loopholes.

The cow spent less than a year on the Alabama farm, which has not been identified. Investigators are trying to find sale records and other documents to determine where the cow was born and raised and to find cows from her original herd.

They're also looking for offspring and have located one of her calves. The six-week-old calf has been shipped to a department laboratory in Ames, Iowa, for observation, the department said Thursday.

Tissue samples from the cow will be sent to the lab for DNA analysis and used to match siblings and offspring. Those efforts are precautionary; it is unusual to find mad cow disease in more than one animal in a herd or in the animal's offspring, the department said.

The cow, a red crossbreed, was unable to walk — a "downer" cow — when the local vet examined her last week. The vet killed the cow and removed brain samples for testing, because downers are considered at risk of having mad cow disease.

Follow-up tests indicated the presence of mad cow disease. The government will compare DNA collected Thursday with the original samples to make sure it exhumed the right cow.

The department is consulting with other agencies to decide how to dispose of the carcass, according to DeHaven.

Mad cow disease is the common name for a deadly nerve disorder known as bovine spongiform encephalopathy, or BSE. Eating meat products contaminated with BSE is linked to variant Creutzfeldt-Jakob Disease, a rare but fatal nerve disease.

Two other cows have been diagnosed with mad cow disease in the U.S. The first case was confirmed in December 2003 in a Washington state cow that had been imported from Canada. The second was confirmed last June in a Texas-born cow.