Reuters:

Pet food tainted with the chemical melamine was found in feed rations on a California hog farm and may show up on other U.S. farms, state and federal officials said on Friday.[..]

California officials said Diamond Pet Foods sold pet food to American Hog Co., which used it as a feed ingredient. Tests found melamine in feed at the farm and in urine from the hogs.

Richard Breitmeyer, the state veterinarian, said it was "not uncommon" for pet food makers to sell scrap material to feedlots.

"In the course of our investigation, we may find similar situations in other parts of the country," said Stephen Sundlof, head of the Center for Veterinary Medicine at the U.S. Food and Drug Administration, referring to sales of scrap pet food.[..]

State and U.S. Agriculture Department officials said there was no evidence that pork products from the farm entered the food supply but that they were still tracking the whereabouts of all the hogs produced there since April 3. Some 126 of the hogs are known to have been slaughtered for meat

This story just gets worse and worse.