WASHINGTON — The secretary of agriculture on Thursday resisted calls from Democratic senators for a complete ban on so-called downer cattle — those unable to walk — from entering the food supply.

In the wake of the largest beef recall in U.S. history, Agriculture Secretary Edward T. Schafer announced new steps to ensure the safety of the country's meat supply, including more random inspections of slaughterhouses and immediate audits of plants that supply meat for federal programs.

But Schafer contended downer cattle could occasionally enter the food supply safely, in accordance with USDA rules, after an additional inspection by a veterinarian.

"The rules say if one goes down you call the veterinarian to make a judgment," Schafer told a Senate hearing.

"Today I'm convinced the rules in place are such where we are protecting the supply," he said.

Schafer ran into resistance from Sen. Herb Kohl, D-Wis., chairman of the Senate Appropriations agriculture subcommittee.

"We cannot allow a single downer cow to enter our food supply under any circumstances," Kohl insisted. He also urged Schafer to install cameras in slaughterhouses and take other steps to ensure meat safety.

It was Schafer's first Capitol Hill appearance since the emergence of video — shot by the Humane Society of the United States — showing workers at Westland/Hallmark Meat Co. in Chino, Calif., shoving and kicking sick, crippled cattle, forcing them to stand by using electric prods, forklifts and water hoses.

In response, the Agriculture Department shut down the plant and has since ordered the recall of 143 million pounds of the company's beef — the largest recall in U.S. history — because the company didn't prevent downer cattle from entering the food supply. Downers, those too sick or injured to walk, pose a greater risk of illnesses such as mad cow disease.

The Hawai'i Department of Education is sending 266,000 pounds of the recalled beef to its landfills.

Schafer insisted his agency is taking the problem seriously and will investigate fully.

"It is extremely unlikely that the mishandled animals pose a risk to human health," said Schafer.

"We are going to pursue these investigations wherever they lead and pursue whatever corrective actions may be called for," he said.

Schafer's testimony came a day after the Humane Society sued USDA over what it calls a loophole allowing downer cattle into the food supply.

In 2004, the USDA tightened regulations to prohibit the slaughter of all "downer" cows after a case of mad cow disease was discovered in Washington state. The lawsuit alleges that under last year's change, cows that fell down after an initial veterinarian inspection but appeared otherwise healthy were allowed to be slaughtered.

Schafer contended that in that situation downer cattle are supposed to be inspected again by a veterinarian and then can be safely slaughtered and consumed.

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Associated Press Writer Frederic J. Frommer contributed to this report.