Birds were reared and kept in a deep litter system prior to the experiment. At 62 weeks of age
birds were transferred to individual cages measuring
43 cm × 43 cm × 45 cm (length × width × height). The feed
trough was placed at the front and a nipple drinker at
the back of the cage. Each cage was supplemented with
a perch of 20 cm length. The cages were separated by nontransparent boards so that the birds had no physical or
visual contact with their neighbours. The hens were kept
in a ventilated windowless room at a constant temperature
(20 ◦C). Lights were on from 0400 until 1800 h. The Hohenheim University mash layer ration (17.2% CP, 11.1 MJ/kg)
and water were provided ad libitum. The test phase started
after 1 week of adaptation to the experimental situation.