http://www.liferesearchuniversal.com/petfood.html#soylentThis link has a lot of info on it.
Poluted Pet Food
After receiving a question regarding the manipulation of foods both for people and animals we thought it appropriate to reprint, with permission, the following studies as one cannot divorce one from the other when dealing with the "food chain". If animals' food is being poluted and adversely affecting the health of the animal then it only renders to reason that this is passed on by the consumption of said animals. Therefore we thank the people at Nexus Magazine and Earth Island Journal for contributing to this health information.
"As the American Journal of Veterinary Research explains, this recycled meat and bone meal is used as "a source of protein and other nutrients in the diets of poultry and swine and in pet foods, with lesser amounts used in the feed of cattle and sheep. Animal fat is also used in animal feeds as an energy source." Every day, hundreds of rendering plants across the United States truck millions of tons of this "food enhancer" to poultry ranches, cattle feed-lots, dairy and hog farms, fish-feed plants and pet-food manufacturers where it is mixed with other ingredients to feed the billions of animals that meat-eating humans, in turn, will eat".
"In California, only eight field inspectors regulate a rendering industry that feeds the animals that the state's 30 million people eat ."