A recent lawsuit filed against Nestle Purina PetCare Company is claiming that one of the company's most popular dog food brands contains toxins that are poisoning and even killing people's pets.http://www.nbcnews.com/news/us-news/lawsuit-claims-purinas-beneful-poisoning-killing-dogs-n312176
If you read the ingredients you may understand better. If it says chicken parts, that could be head, beaks, feathers, skin, fat, etc.
The ingredients my be corn or corn/soy products. All they are trying to get into the dog food is protein (animal skin would supply this), carbohydrates (fat or starches) and fibre (could be sawdust) Calcium (maybe ground up bone), could be cartilage etc.
Try table scraps, you know then what your dog it eating.
Lawsuit Claims Purina Beneful Is Poisoning Killing Dogs