WASHINGTON (CNN) -- In his first public testimony since his company's product became the subject of the largest meat recall in U.S. history, the president of Westland/Hallmark Meat Co. acknowledged Wednesday that at least two "downer" cows depicted in hidden-camera videos appeared to have entered the U.S. food supply.

He previously had denied that any had gotten into the food supply.

Still, there was "less than a minute chance of that product being contaminated," Steve Mendell told the House Committee on Energy and Commerce's Subcommittee on Oversight and Investigations.

Wednesday was the latest in a string of hearings prompted by the company's voluntary recall on February 17 of 143 million pounds of beef -- representing the Chino, California, plant's output since February 1, 2006.

The recall was ordered amid uproar over the release of video filmed with a hidden camera over a six-week period by a worker at the plant who was also working for the Humane Society of the United States.

The video, which was released to the media January 30, showed downer cows being chained, dragged, rolled, kicked and jabbed in an effort to make them stand so they could be led into the chute for slaughter.

As the animals screamed, workers prodded them with forklifts, shocked them and shot powerful streams of water into their nostrils.

Excerpts of the video were played for the committee members.

In his written testimony, delivered under oath, Mendell said that "the activities shown on the video are not 'food safety issues.' The cows shown in the video could not walk, were designated to be euthanized and were not put into commerce."

But after being shown excerpts of the videos showing two such cows in the "kill chute," he acknowledged that it "would be logical" to conclude that at least two such cows had entered the food supply.

Mendell said that he had not seen the videos before, but he expressed skepticism that the animals could have threatened anyone's health.

No reports of illness have been linked to the meat, though experts say it could be years before some diseases might emerge.

Cattle that can't walk to slaughter on their own are deemed "downer cows" because they may be sick. Downer cows are not allowed to enter the food supply because they are associated with a higher risk of mad-cow disease, a fatal brain-wasting syndrome that takes an average of 13 years to appear.

Of the 15 cases of mad-cow disease diagnosed in cattle in the United States and Canada, 12 were among downer cows. The latest case, in Canada, was reported February 26.

Asked what went wrong at Westland/Hallmark, Mendell said, "Obviously, there was a breakdown in our training or our programs to allow that kind of behavior to occur."

He said that, since the release of the videos, he has ordered the installation of 17 video cameras "that cover every square inch" of the yard and the unloading area.

Mendell, who appeared Wednesday only after being subpoenaed, apologized for not having attended a February 26 hearing on the matter. Other matters were more pressing, he said.

"I was overinundated with phone calls, news reporters, and my business was in the middle of the biggest recall in U.S. history," he said.

Mendell said he disagrees with the U.S. Department of Agriculture's handing of the recall, which has cost hundreds of millions of dollars and is likely to result in the permanent closure of his company.

"I think, in my humble opinion, that USDA could have contacted Alameda, our local area office, talked to the veterinarian in charge, talked to my area supervisor and thought about this a little bit before the recall."

He said that safeguards in place -- removal of high-risk spinal cord tissue -- would have ensured the safety of the beef.

Wayne Pacelle, president and CEO of the Humane Society of the United States, said Mendell's testimony raised serious questions.

"This is a guy who claims he had a good training program; this is a guy who had third-party audits; this is a guy that says USDA has a full complement of inspectors at his plant," he said.

"Well, why did things go so badly? If other plants are making similar claims, should we have confidence in what they're saying?" E-mail to a friend

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