There are several sources of protein for animal feed. The meat meal, fish meal, poultry by-product meal, blood meal and feather meal. Bone is included as source of calcium. A cow might be eating an organ of his own kind unknowingly. Perhaps he would not eat such if he knew.
Protein sources are by-products of slaughtering and further processing. Parts that are not suitable for human consumption but still safe for animal to eat.
Converting of bones, feathers and other trimmings to animal feed is good idea. The supposed waste materials turned to worthy and converted to cash.
However, animal feed should be as clean as human food. Why? Livestock are raised for food. In short, we are also eating what they consume. Nutrient supplements, medicines, hormones and antibiotic and even diseases. Animal protein sources should come from healthy animals. Some manufacturers might intentionally include parts from double dead pigs, cows and chicken.
Mad cow disease is one the diseases that passes through food chain. A meat from infected cow eaten by human. Meat, bone or blood that are included in feed formulation – eaten by animals. Mad cow disease occurs in brain and spinal column. Consumption of these parts is prohibited. But eating other parts might also transfer infection.
The disease incubation period is approximately 30 months to eight years. Once the symptoms manifest, the source would be very hard to trace. Foods eaten eight years ago are almost impossible to remember. The more impossible when loosing insanity.