The intensification of animal production during the past half century has consisted of two key elements.
One is a change in production methods. Until about 1950, farm animals in industrialized countries were raised by fairly traditional methods that relied on labour for routine tasks such as feeding and removal of manure and that generally involved keeping animals outdoors, at least part of the time. After the Second World War, there emerged a new generation of "confinement" systems that generally kept animals in specialized indoor environments and used hardware and automation instead of labour for many routine tasks. Confinement methods came to predominate in industrialized countries for those species that are largely fed on grain and other concentrated feed, notably in the production of poultry, pigs, veal calves and eggs. The shift towards confinement was much less pronounced for predominantly forage-fed animals. For example, many beef cattle in North America, although concentrated in large outdoor feedlots where they are finished on grain-based diets for their last few months, are raised for much of their lives in traditional grazing systems, and most sheep and goats continue to be raised in traditional, non-confinement systems (Fraser, Mench and Millman, 2001).
While this change was occurring, production was becoming concentrated on fewer and fewer farms. Annex Table 1 shows the trends in Canada and Denmark, selected as two countries with large animal industries. The chicken and pig sectors, which moved strongly toward confinement housing, showed a pronounced decline in the number of farms raising these species. For cattle the decline was slower, and there was little or no consistent change in the number of farms raising sheep.
For the purpose of this paper, "intensification" will be used to refer to the above two changes: towards more confined production systems and towards the concentration of production on fewer units. Intensification (in this sense) was also accompanied by large increases in production. In the years 1961 - 2001, world production increased rapidly for poultry meat and pig meat (Annex Table 2). In contrast, the production of bovine meat, mutton and goat meat, products derived from species that were much less subject to intensification, showed more modest increases. In fact, these latter increases were roughly proportional to the rate of growth of the human population, which approximately doubled during the same 40 years.