From The Truth About Pet Food newsletter:
"What we don't know about the ingredients used to make dog foods and cat foods is staggering. Those in charge of defining pet food ingredients provide the industry a means to hide the real truth of quality from the petsumer. Thanks to a patent provided to Mars Incorporated (maker of Pedigree, Nutro, Whiskas pet foods), we are provided a bit of insight into where and how some pet food ingredients are obtained. This isn't pretty.
Patent Assignee: Mars Incorporated
Title: Method of utilizing offals for pet food manufacture
Publication Date: 8/18/2009
Link: Method of utilizing offals for pet food manufacture - Mars Incorporated
Below are excerpts from the patent (bold added):
The invention claimed is:
1. A method for the recovery of commercial waste parts for use in the manufacture of commercial pet food products, comprising the steps of: collecting waste parts selected from the group consisting of hearts, kidneys, lungs, liver, spleen, tripe, meat offcuts, chicken viscera, chicken heads and feet, chicken pieces, and chicken necks from the commercial processing of animals; size-reducing the waste parts..."
For the rest follow this link: Patent Gives Insight into Pet Food Ingredients