It is estimated that worldwide, approximately 80 percent of eggs are produced in battery cages (Canadian Coalition for Farm Animals, 2005). This is in spite of significant effort by the European Union (EU) to push towards other housing systems (Savory, 2004). A significant percentage of eggs from caged hens worldwide arises from North America and Asia egg farming operators, who continue to use battery cages (Duncan, 2001).

Laying hens in the United States are primarily housed in battery cages (Pohle and Cheng, 2009). This is also the case in Canada today (Agriculture and Agri-food Canada, 2003).

Prior to the invention of battery cages, most laying hens were housed in free-range systems. Egg farmers ran small-scale operations and all egg collection was manual.
woodleywonderworks. (Photographer). (2008, June 23). [Semi] free range chickens [digital image]. Retrieved from https://flic.kr/p/4YitAe

By the middle of the 20^th Century, an intensive mechanization of the industry was witnessed as the battery cage was introduced (de Boer and Cornelissen, 2002). Originally, battery cages were an innocent response to increase hen productivity following breakthroughs in the industry regarding nutrition and breeding (Duncan, 2001). In comparison to keeping birds in floor housing systems, cages allowed for the increase of animal production through mechanization, the permittance of higher stocking densities, and a lower economic costs on a per hen basis. The use of cages also allowed farmers to reduce or avoid outbreaks of cannibalism in their flocks which was more common in larger flocks kept on the floor (Hilbrich, 1985; Hansen, 1993; Abrahamsson and Tauson, 1995). It also prevented the significant and erratic concern of coccidiosis common to flocks kept on the floor (Engström and Schaller, 1993; Morgenstern and Lobsiger, 1993), as well as reducing dust and ammonia levels to benefit the working conditions of farmers (Hauser, 1988; Kangro, 1993).

However, by the mid-1970s, work on alternatives to battery cages began. Perhaps this initiative was led by Swedish scientist Ragnar Tauson who, alongside his colleagues, investigated the source of various basic health problems combatted by laying hens kept in battery cages. Among these health issues identified were significant foot lesions, neck lesions, overgrown claws, and loss of feathers (Fraser, 2008). Tauson’s findings identified the cause of these health effects to be related to the battery cage housing system. The results were very influential with various industry stakeholders including cage manufacturers and those involved in writing regulations and further work on alternative designs was undertaken. Much of this work was funded by the governments of northern European countries (Appleby, 2003).

Battery cages are a housing system used for laying hens worldwide in modern poultry egg production (Banga-Mboko et al., 2010). It is estimated by Awoniyi (2003) and corroborated by Peterman (2003) that up to 90% of all laying hens in commercial production are housed in battery cages in most developed countries today. While some European countries are moving away from this practice today (Tauson, 1998), the use of cages is actually increasing in developing countries (Bell, 1995).

                                             Source: TNAU Agritech Portal

A battery cage is a small metal wire cage of approximately 16” by 18”. These cages are most commonly arranged back-to-back in three rows of identical small metal wire cages connected together like battery cells, hence the name. Further, these rows are stacked on top of one another. This formation is called ‘tier cages’. Two other common arrangements include ‘California cages’ (stair-step system) and ‘flat deck cages’ (single tier cages) (Blount, 1968). In this housing system, hens have access to automatic management-controlled feed and water. Further, the wire cage floors are sloped so that eggs roll down to the egg tray for easy automated collection. Similarly, hens’ droppings fall through the wire cage floor either onto a conveyor belt or into a pit for disposal. While the space provided for each hen varies across each farm, the space allowance in Canada is 423 cm2/hen or 65.6 in2/hen (SPCA, 2009). To put things into perspective, the space available to each hen in a battery cage is often described as less than the size of a sheet of A4 paper.