The co-owner of a Petaluma slaughterhouse tied to a massive meat recall pleaded guilty to charges of selling cows with eye cancer and agreed to cooperate with prosecutors in their case against three other defendants.

Robert Singleton, 77, faces up to three years in prison and is free on $50,000 bond, according to a copy of the plea agreement, which was reached Friday.

Singleton co-owned Rancho Feeding Corp., which was shut down in February by federal inspectors after a recall of nearly 9 million pounds of meat.

The recall included grocery chains such as Kroger, Food 4 Less and Wal-Mart. Nestle also issued a voluntary recall for its Philly Steak and Cheese Hot Pockets.

Singleton admitted purchasing cows exhibiting eye cancer, which is deemed unfit for human consumption, according to federal laws.

Workers severed the heads of those cows to disguise them as healthy cows for processing and inspection.