Their brands included Meow Mix, Kibbles 'n Bits, Milk-Bone, 9Lives, Gravy Train, Nature's Recipe, Canine Carry Outs, Pup-Peroni, and Milo's Kitchen, among others.

Smucker Company would acquire Big Heart Pet Brands for $5.8 billion.

The source was identified as likely to be that animals that had been euthanized with pentobarbital had been used for making the dog food.

While the levels detected were not considered lethal, the drug is not legally permitted at any concentration in pet food.

After declining an on-camera interview, the FDA stated that it would "investigate the matter and take appropriate enforcement action".