WASHINGTON — Agriculture Secretary Ed Schafer announced Tuesday a total ban on the slaughter at meat plants of cows too sick or weak to stand.

The planned change comes in the wake of the nation's largest beef recall. It would shut down an exception — which critics call a loophole — that allows a small number of so-called "downer" cattle into the food supply if they pass veterinary inspection.

Downer cows pose increased risk for mad cow disease, E. coli and other infections, partly because they typically wallow in feces. They are already mostly banned from slaughter, but under current rules can be allowed in if they fall down after passing an initial veterinary inspection, and then are re-inspected and pass that second inspection, too.

Some lawmakers and the Humane Society of the United States have lobbied Schafer to eliminate that exception, and the meat and dairy industry last month reversed its opposition and endorsed the change.

Schafer announced the planned new rule to reporters following a 60-day review of conditions at the nation's slaughterhouses. The department hopes to finalize the rule within several months.

The review was prompted by a 143-million-pound beef recall in February, ordered after the Humane Society released undercover video showing employees abusing downer cows at Westland/Hallmark Meat Co. in Chino, Calif. Downer cows at the plant were forced to slaughter without the required second veterinary inspection, which is why the recall was ordered. Agriculture officials have insisted there was minimal if any health risk.

Schafer said that no such violations have been found at other slaughterhouses. He said the rule change was not being done for public health reasons but should increase consumer confidence by eliminating confusion about the handling of downers.

"I don't think we can justify the confusion that takes place in the consumer's mind," Schafer said.

He also said the change should improve handling of cows by cattle producers and slaughterhouses, "as there will no longer be any market for cattle that are too weak to rise or walk on their own."

The change would affect a small number of cows. Out of 34 million cows slaughtered in 2007, around 2,700 fell down after the initial veterinary inspection and were re-inspected, Schafer said.

Of those, less than 1,000 were then approved to go to slaughter, he said.

The American Meat Institute and other industry groups praised Schafer's announcement, and it also was welcomed on Capitol Hill, where legislation to enact a total downer ban has been proposed in the House and Senate.

In 2004, the USDA tightened regulations to prohibit the slaughter of downer cows after a case of mad cow disease in Washington state. But in finalizing the rule last year, the department created the exception allowing the re-evaluation of cattle that fall down after they pass initial inspection. Prior to Tuesday, Schafer had defended the exception, saying it was not fair to cattle owners to ban the slaughter of cows that may be perfectly safe to eat and just have a broken limb.

The Humane Society sued the Agriculture Department in February over the exception but withdrew the lawsuit several weeks ago amid positive discussions with Schafer, said Wayne Pacelle, Humane Society president and chief executive.

Pacelle praised Schafer over Tuesday's announcement but told reporters on a conference call that the rule should take effect immediately and also cover other livestock and intermediate markets such as auction sites where the Humane Society has documented abuse.

Pacelle disputed Schafer's claim that there was not a public health concern with the downer exception, noting that most mad cow cases in North America have been from downers.