Restricting laying hens' litter access leads to a rebound effect in wing flapping and dust bathing behavior

Cage-free laying hen housing can lead to floor eggs, and keeping hens from litter in the morning can limit this problem. However, space-demanding and welfare-relevant behaviors such as wing flapping (WF) and dust bathing (DB) may be compromised in ways that need to be understood. A total of 1152 birds were allotted between two rooms, each equipped with 3-tiered enclosable aviary systems further subdivided into 4 units each. One room was assigned to enclosed (PARR) birds deprived of litter access between 0100 and 1200 from 17 to 32 weeks of age (WOA), while the other room served as a control (CON) with continuous litter access. WF was continuously observed for 30 minutes at 0600, 0900, 1200, 1500 and 1800, while DB was scan-sampled for 15 seconds every 5 minutes for 3 hours (1100-1230, CON or 1200-1330, PARR; 1430-1600, both) from 17 until 44 WOA. Comparisons of treatments at the same hours of day and 0, 3, and 6 hours past litter access were performed for WF. Comparisons between 1.5-hour blocks were carried out for DB. The sum of WF and DB per time block was analyzed with generalized linear mixed models, while Spearman correlation tests were performed between the number of WF and DB at litter provision and total birds on litter every 3 or 5 minutes, respectively. Hens performed more WF and DB in PARR than CON when litter access was provided at 32 and 44 WOA (P < 0.05). Amount of WF at 32 WOA was negatively correlated with number of birds on litter only in CON birds (r = -0.651; P < 0.001), while a negative correlation was observed for DB frequency in PARR hens at the same age (r = 0.374; P < 0.01). These results suggest detrimental effects of enclosure on hens' performance of WF and DB, which lead to a rebound effect as soon as birds gain litter access. Furthermore, WF frequency may vary with age, and hens' need to WF may weigh more than crowded litter discomfort after spatial restriction.