While feedlot beef cattle spend the first six to eight of their lives grazing on pasture, they are then sent to “feedlots” or “finishing” lots. Their diet shifts from fresh grasses and hay to a grain-based feed. Because cattle are ruminants, the switch to grain results acidifies their digestive system, allowing acid-tolerant bacteria such as e coli 0157 bacteria to grow. The pathogen can contaminate meat during slaughter and be passed on to consumers.
As many as 100,000 cattle can be confined to one feedlot. The overcrowded, stressful conditions provide for rapid spread of diseases (insert picture feedlot).
Because of the centralization of the cattle industry, beef animals are also subjected to long distance transportation to slaughter, another major source of stress for the animals. While in transport they spend long periods without food, water, or rest, and often suffer injuries or become ill.
The Canadian Coalition for Farm Animals fact sheet on beef cattle provides more information.