Some animals get offal because the farmers' avarice , that may look lucrative, but it was disastrous for the British beef trade and for the European beef sale. In the offal the British cows ate, there were remains of sheep that were infected with an id of the Creutzfelt Jacob syndrome. The bacteria that spread this disease changed and changed till they could make leap from a sheep to a cow. This is how some cows were infected with this wasting disease. When people eat infected beef they can get sick too, but nobody has ever proved that this disease could be leap up from cows to human. Because of the bad circumstances that occur and because of the bad feed they sometimes get, many animals get very weak after a longer time on a farm.  The only way to keep them alive is to give the power food  But sometimes you can find small pieces of that power food in the meat, especially calf meat. 
The fact is that these remains are not healthy for the people. That's why most kinds of power food are prohibited in the EEC, but for some farmers money is the only thing that counts, and they try to find ways to keep the risk of being caught on using prohibited things as low as possible 

*Lean meat 
 

 
 ensilaged grass