Animals like cattle, sheep and goats are called “Ruminants” and are vegetarians by design with the ability to easily digest plant fibers. This ability is due to their four compartment stomach that includes a large fermentation “vat” called a rumen.
Rumination involves swallowing grass, soaking and mixing it in the fluid rumen contents, regurgitating a cud, re-chewing it, then re-swallowing it.
Animals fed inappropriately on dry grain diets suffer from numerous gastrointestinal and other diseases. By definition, then, grain feeding means suffering for the animal. It also can mean suffering for the humans who ingest their meat, eggs, or milk. Grain feeding alters the animals' intestinal flora, increasing opportunities for the growth of pathogens such as E. coli (in cattle) and Salmonella (in poultry). The intestines of cattle fed only grass or hay are free of virulent E. coli, and chickens raised entirely on pasture are free of Salmonella. Mad cow disease is unknown among cattle fed entirely on pasture and hay.