THE laying hen has undergone considerable artificial selection pressure over the past century, to increase its egg output in order to provide a protein-rich food source for humans. While its wild counterpart will lay just five to six eggs per breeding season, modern breeds will lay in excess of 300 eggs per year (Lever 2011). With increased egg output, we have also imposed changes in the way in which laying hens are housed (Table 1), with eggs largely produced in loose-housed systems (barn and free-range) in the 1950s, which moved to mainly cage production through the 1960s to 2000s, because cages reduced disease and mortality and were more economic (Duncan 2001). Then, as scientific research investigated the behavioural needs of animals, combined with greater affluence, consumer concerns over more welfare-friendly food production, and the ban on the conventional cage, which takes effect from 2012 (European Commission 1999), we are now moving back to a large proportion of egg production taking place in loose-housed systems. View this table: Table 1 Changes in the percentage of eggs from different production systems in the …