Consuming meat from cattle with eye cancer involves no known disease risk to humans and the beef sometimes passes federal inspection and makes it to the public's dinner plate, say food safety experts.
The issue surfaced last week with allegations that the embattled Rancho Feeding Corp. of Petaluma may have circumvented federal regulations by slaughtering cancer-stricken cows.
Confirmation came in a U.S. Department of Agriculture Food Safety and Inspection Service letter that said an investigation showed Rancho sold cattle "likely affected with epithelioma of the eye."
The Jan. 14 letter, first reported Wednesday by the Los Angeles Times, said that regulators found two cattle heads that had made it to market intact and with "skin still attached, and had no incisions for the four pair of lymph nodes on the head, which normally are incised for inspection."
The cattle heads did not have the USDA's mark of condemnation, which would prevent them from being sold, the letter said.
Rancho's plant — shuttered on Feb. 9 — is under investigation by the USDA and the U.S. Attorney's Office and the 8.7 million pounds of beef and veal produced there last year have been recalled.
No illnesses related to the meat have been reported, and much of it presumably has been consumed.
A call to Rancho co-owner Robert Singleton on Thursday was not returned.
The business is known to have purchased retired dairy cattle for slaughter and sale, and handled slaughtering for custom beef ranchers who market their own meat.
Post-mortem inspection of slaughtered cattle starts with the head, and officials have the option of rejecting either the head or the entire carcass of an animal with eye cancer, a former USDA veterinarian told The Press Democrat.
"It's a judgment call," said Daryl Jacobs, who retired in 2012 after eight years as supervising veterinarian at an Idaho slaughterhouse. "Just one bad eye will not condemn a cow."
As long as the head is discarded, "the rest of that meat is fine," Jacobs said.
In his own experience examining about 80,000 cows, Jacobs said he probably had approved some with eye cancer that should have been condemned, surmising that other inspectors have done the same.
More often, Jacobs said, he condemned cows that could have been passed along to meat markets.
Two other food safety experts said people could eat the meat from cows afflicted with eye cancer.
"I think it's pretty clear that the risk is minuscule," said Jim Cullor, a veterinarian and director of the Dairy Food Safety Laboratory at UC Davis.
Cullor said there is "no known transmission" of eye cancer from animals to humans through food. Public health officials maintain surveillance over possible food-borne disease outbreaks, he said. "If something is wrong it will pop up."
Eye cancer in cattle is "not a specific food safety threat," said Frank Garry, a professor in the Department of Clinical Sciences, Food Animal Medicine and Surgery at Colorado State University.
Even cancerous tissue itself is not harmful, he said, but the USDA rightly considers it inedible. "Nobody wants to eat abnormal tissue and the rules reflect that," Garry said.
The key decision at a slaughterhouse is whether the cancer is confined to the eye globe, in which case the rest of the carcass is suitable for food, or whether the cancer may have spread through the animal's lymph system, justifying disposal of the entire carcass, he said.