A second office within the US Department of Agriculture has begun investigating a Petaluma slaughterhouse that has temporarily ceased operations while recalling a year's worth of processed beef, the agency reported Tuesday.

"USDA's Office of the Inspector General is conducting an ongoing investigation into Rancho Feeding Corporation," said a statement released Tuesday by the agency's Food Safety and Inspection Service.

The statement noted that the administrator over the inspection service had separately "directed an immediate and thorough examination of the firm's practices, procedures and management."

The 39-word statement was the most detailed to date on the agency's investigation of the the North Bay's last remaining beef processing facility.

On Saturday the USDA announced that Rancho had initiated a recall of 8.7 million pounds of beef, essentially all the meat the company had processed in 2013.

In its news release, the agency asserted that Rancho "processed diseased and unsound animals" without a full inspection. The meat products are "unsound, unwholesome or otherwise are unfit for human food" and must be removed from commerce.

There are no reports of anyone becoming ill after eating the beef.

Robert Singleton, who owns Rancho with partner Jesse "Babe" Amaral, on Monday confirmed the company had voluntarily ceased processing and was compiling a list of affected companies. Singleton said the company undertook the recall out of "an abundance of caution" but declined comment on the government's allegations.

Other than the news release Saturday and the statement on Tuesday, officials with the US Department of Agriculture have declined to elaborate on the underlying reasons for the recall or the breadth of their investigation.

The recall affects all beef processed at Rancho between Jan. 1, 2013, and Jan. 7, 2014, a USDA spokesman said. The carcasses and other parts, commonly referred to as offal, were shipped to retailers and distributors in California, Florida, Illinois and Texas.

Last month the USDA announced that Rancho was recalling 41,683 pounds of meat produced on Jan. 8. The agency asserted that the meat didn't receive a full federal inspection.

You can reach Staff Writer Robert Digitale at 521-5285 or robert.digitale@pressdemocrat.com.