One of my cats was a victim of the poisoned dog food

My mom was feeding her dog the nutro something the canned meat stuff and my cat would lick at it...We lost my moms rott (not sure if it was the food, cuz she was sick before that) but my cat went into renal failure, he was on an IV in the vet for almost a week but it was too late...
How can you tell if the food has animal parts in it?!? Thats really disgusting.