In the 1950s, the transition towards what is now known as factory farming picked up speed with farmers beginning to keep their livestock indoors. Eventually animals were being kept in very close quarters, with the use of antibiotics and other interventions to counteract the natural effects of these living conditions. Factory farming has grown to become a major source of global meat production, and a major source of contention for environmental and animal rights activists. Major disease outbreaks in livestock populations have largely been confined to the factory farming era, as the cramped conditions facilitate the spread of diseases such as Foot-and-Mouth and BSE (Mad Cow Disease.) Concurrently, farming productivity has skyrocketed; the average US livestock farmer fed 25.8 people in 1960, while in 2005 the average farmer fed 155 people.
Image via aldf.org