DES MOINES, Iowa -- Federal government regulators proposed changes Friday in the way most hogs slaughtered for meat in the United States are processed in a series of new rules officials say improve industry practices but critics say could imperil food safety.

The new rules would allow hog slaughter plants to voluntarily join a new proposed inspection system that would put plant employees in charge of determining which animals are unfit for processing. Government inspectors who currently perform this function would be moved to other areas of the plant focused more on food safety, said U.S. Department of Agriculture acting deputy under secretary for food safety Carmen Rottenberg.

The proposed rules are similar to ones rolled out in 2014 for the poultry industry.

Critics have said such changes turn too much of the inspection and food safety testing over to the companies, creating increased risk of foodborne illnesses from contaminated meat as well as an increased risk of inhumane treatment of animals.

"We think that food safety is going to suffer from this," said Tony Corbo, a senior lobbyist at Food & Water Watch, a Washington-based advocacy group that is calling for the USDA to drop the proposed rules. "We opposed what they did in poultry and we're opposing what they're doing here. This is a belated Christmas gift to the industry."

Rottenberg insists the changes could improve food safety and said they still would require government inspectors to look at all hog carcasses processed.

"There is no single technology or process to address the problem of foodborne illness, but when we focus our inspections on food safety-related tasks, we better protect American families," she said.

The proposed rules also would increase the number of hogs plants could process by revoking limits on line speeds and allowing plants to determine their own speeds. Corbo argued the move could endanger workers and reduce quality control.

Maximum line speeds are currently set at 1,106 hogs per hour, meaning each line in a plant is allowed to handle that number of carcasses each hour. The USDA said five pilot plants operating at their own established speeds have operated efficiently but safely.

Corbo said data he's collected indicate the pilot plants have had significantly higher noncompliance reports in key areas, including sanitation.

The USDA's Food Safety and Inspection Service, which is proposing the rules, said the new system is unlikely to result in increased bacterial contamination of hog carcasses and could lower it, "which in turn may result in fewer human illnesses."

Companies may choose not to adopt the new rules and could continue to operate under the existing inspection system.

The voluntary inspection program would apply only to those processing plants slaughtering market hogs, animals about six months old weighing about 250 pounds, which make up about 96 percent of the pork products sold to consumers.

After officially posting the rules in the next few days, the agency will begin taking comments, which could lead to changes in the proposal. No date has been set for enactment.

A second set of rules proposed Friday would be mandatory and require all pork processing plants to implement their own new daily documentation on how they prevent bacterial contamination of carcasses and procedures for microbial testing.

The USDA has been working on changes to pork processing since 2002, Rottenberg said.

The agency said the U.S. has 612 swine slaughter plants under federal inspection. They process about 118 million hogs a year.

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