Lets not forget Mad Cow Disease, I have big reservations about all these bits and pieces going into the pet food.  I know dogs eat all sorts of crap, this is why I feed mine home prepared food and fresh bones etc.  I have also had dogs grab dead animals and scoff them down before I could grab it and they have had no ill effects at all, and I have less of a worry about that than I do about what humans are adding.  I can remember in the early 70's, I was working then for the vet I am working for now, we had an unconscious dog bought in, all vitals were fine, it was just out to it, I can remember the client was also a farmer and the boss had euthanised a cow for him the week prior with lethal injection, the farmer had fed this meat to his dog, hence, the dog was under the effect of anaesethic. 
The dogs and cats from the main shelter here are made into blood and bone garden fertilizer. 


Epidemic in British cattle

Cattle are naturally herbivores, eating grass. However in modern industrial cattle-farming, various commercial feeds are used, which may contain ingredients including antibiotics, hormones, pesticides, fertilizers, and protein supplements. The use of meat and bone meal, produced from the ground and cooked leftovers of the slaughtering process, as well as from the carcasses of sick and injured animals such as cattle or sheep, as a protein supplement in cattle feed was widespread in Europe prior to about 1987.^[3] Worldwide, soybean meal is the primary plant-based protein supplement fed to cattle. However, soybeans do not grow well in Europe, so cattle raisers throughout Europe turned to the cheaper animal byproduct feeds as an alternative. The British Inquiry dismissed suggestions that changes to processing might have increased the infectious agents in cattle feed, saying "changes in process could not have been solely responsible for the emergence of BSE, and changes in regulation were not a factor at all."^[26] (The prion causing BSE is not destroyed by heat treatment.)

The first confirmed animal to fall ill with the disease occurred in 1986 in the United Kingdom, and lab tests the following year indicated the presence of BSE; by November 1987, the British Ministry of Agriculture accepted it had a new disease on its hands.^[27] Subsequently, 165 people (until October 2009) contracted and died of a disease with similar neurological symptoms subsequently called (new) variant Creutzfeldt-Jakob disease (vCJD).^[5] This is a separate disease from 'classical' Creutzfeldt–Jakob disease, which is not related to BSE and has been known about since the early 1900s. Three cases of vCJD occurred in people who had lived in or visited the UK – one each in the Republic of Ireland, Canada and the United States of America. There is also some concern about those who work with (and therefore inhale) cattle meat and bone meal, such as horticulturists, who use it as fertilizer. Up-to-date statistics on all types of CJD are published by the National Creutzfeldt-Jakob Disease Surveillance Unit (NCJDSU) in Edinburgh, Scotland.

For many of the vCJD patients, direct evidence exists that they had consumed tainted beef, and this is assumed to be the mechanism by which all affected individuals contracted it. Disease incidence also appears to correlate with slaughtering practices that led to the mixture of nervous system tissue with hamburger and other beef. An estimated 400,000 cattle infected with BSE entered the human food chain in the 1980s.^{[citation needed]} Although the BSE epizootic was eventually brought under control by culling all suspect cattle populations, people are still being diagnosed with vCJD each year (though the number of new cases currently has dropped to fewer than five per year). This is attributed to the long incubation period for prion diseases, which are typically measured in years or decades. As a result, the full extent of the human vCJD outbreak is still not known.

The scientific consensus is that infectious BSE prion material is not destroyed through normal cooking procedures, meaning that even contaminated beef foodstuffs prepared "well done" may remain infectious.^[28][29]

Alan Colchester, a professor of neurology at the University of Kent, and Nancy Colchester, writing in the 3 September 2005 issue of the medical journal The Lancet, proposed a theory that the most likely initial origin of BSE in the United Kingdom was the importation from the Indian Subcontinent of bone meal which contained CJD-infected human remains.^[30] The government of India vehemently responded to the research calling it "misleading, highly mischievous; a figment of imagination; absurd," further adding that India maintained constant surveillance and had not had a single case of either BSE or vCJD.^[31][32] The authors responded in the 22 January 2006 issue of The Lancet that their theory is unprovable only in the same sense as all other BSE origin theories are and that the theory warrants further investigation.^[33]

http://www.huffingtonpost.com/2010/10/26/fda-approved-rat-hairs-an_n_773608.html#s165326&title=Pizza_Sauce_30