Savory, 2006 – Behavioural responses to different floor space allowances in small groups of laying hens

1. Under Council Directive 1999/74/EC, minimum space allowances per laying hen range from 550 cm² in unfurnished cages to 1111 cm² in alternative housing, and to 40 000 cm² outdoors for free-range hens. In official reports on the welfare of laying hens, there is recognition that knowledge of their space requirements is inadequate.
2. This experiment studied expression of behaviour, including spacing, in five groups of six and one group of five ISA Brown hens aged 21—33 weeks in an adjustable test pen providing 600, 2400, 4800, 7200, 9600, and 12 000 cm² floor area per hen. Each group was tested with every treatment. Home pens provided 2400cm² per hen. The main aim was to identify a hypothetical point at which mutual repulsion equals mutual attraction (a ‘broken stick’ response).
3. Sequencing of treatments was according to a Latin square design, daytime tests lasted 2 h and had no feeder or drinker present, and overnight tests were done with 2400, 7200 and 12 000 cm² per hen with a feeder and drinker present. Groups were video-recorded from above to allow repeated measurements of spacing and other behaviours.
4. In daytime tests, the relationship between mean distance to nearest neighbour and floor space allowance was asymptotic, rather than a ‘broken stick’. The steepest part of the response was between 600 and 4800 cm² per hen. Changes in other behaviours were greatest between 600 and 2400 cm², and there was no significant change above 7200 cm². Spacing behaviour responses at night were the same as by day.
5. It is concluded that any space allowance of less than about 5000 cm² per hen imposes at least some constraint on free expression of behaviour, and that hens would benefit from any increase above the current minimum 1111 cm² usable area in alternative housing.