A series of mishaps and confusion over U.S. testing for mad cow disease raise questions about the government’s credibility and could undermine efforts to convince major trading partners of the safety of American beef, industry and consumer groups said on Wednesday.

The USDA is now investigating a possible third U.S. case of mad cow disease, or bovine spongiform encephalopathy (BSE), in an animal at least 12 years old.

A brain sample from the suspect cow was taken by a local veterinarian in April but was not tested by the USDA until last week. That delay was because the veterinarian “simply forgot” to submit it, the USDA said.

The sample was frozen, a violation of USDA guidelines, and the veterinarian also mistakenly used a preservative that limits the type of mad cow tests that can now be conducted.

“It is not a good image to be broadcasting,” said Philip Seng, president and chief executive of the U.S. Meat Export Federation. “The people in the international markets who would like to keep us out of the markets, they seize upon these points of differentiation.”

The mistakes come just one month after the USDA was criticized for its handling of another BSE case.

In that instance, a 12-year-old Texas beef cow was slaughtered in November and rapid screening tests found no mad cow disease. But USDA’s inspector general in June ordered the case to be reopened for more sophisticated testing, which confirmed mad cow disease.

The USDA also found problems with the handling of the Texas animal’s brain tissue samples and inadequate documentation.

Democratic Sen. Tom Harkin of Iowa, a major beef-producing state, said these types of mistakes prompt Japan, South Korea and other countries to question the safety of U.S. beef.

The USDA said it hoped the new investigation would not impact talks with Japan, historically the top buyer of U.S. beef, and South Korea, the No. 3 market. Final test results are expected next week.

MORE FORGETFUL VETS?

Consumer groups questioned whether other local veterinarians may have forgotten to send samples of suspect animals to the USDA, keeping more cases from coming to light.

The USDA depends on private veterinarians to submit brain samples from high-risk cattle - those unable to walk or that show signs of a nervous disorder.

The USDA has its own veterinarians staffing meat-packing plants, where most cattle are slaughtered. They check the incoming animals for symptoms of disease.

“These two cases call into question how they handle every other case,” said Joe Mendelson, legal director for the Center for Food Safety. “If samples are taken and not being sent in, this speaks to significant gaps in our surveillance program.”

USDA officials defended the testing program, which has administered rapid, screening tests to more than 419,000 cattle in the past 13 months. That marks a tenfold increase from the previous testing rate.

“Every program in every federal agency is going to have its critics. Whenever we see a problem with our programs we fix it,” said Jim Rogers, spokesman for the USDA’s Animal and Plant Health Inspection Service.

The USDA refused to identify the location of the suspect animal now under investigation, or the veterinarian’s name.

The National Cattlemen’s Beef Association, which represents many U.S. ranchers, said it viewed the missteps in the current case as an isolated incident.

Senate Agriculture Committee Chairman Saxby Chambliss applauded the animal health official for finding the suspect animal.

“We had a very alert veterinarian who decided…to take the sample,” the Georgia Republican said. “Thank goodness, we’ve got people out there.”