The effect of litter condition and depth on the suitability of wood shavings for dustbathing behaviour

Although several studies show that fresh wood shavings (FW) are not well-suited as dustbathing substrate for laying hens, little is known about the suitability of wood shavings used as litter in non-cage systems for several weeks (used wood shavings, UW) and the effect of different substrate depths. We compared FW and UW at two different depths of 2 cm (shallow, S) and 20 cm (deep, D) with respect to how stimulating and adequate the substrate conditions are perceived by the hen, indicated by the dustbathing behaviour of Lohmann Silver laying hens. UW were friable and characterised by a greater proportion of small particles <1.4 mm (44%, FW: 25%) and lower dry matter (73%, FW: 87%). In an experimental setup 36 groups of four hens from furnished cages (Aviplus), which were expected to have a relatively uniform and high dustbathing motivation were placed in test pens for 5 h with one of the four substrate quality and depth combinations (n = 9 per substrate condition). The video-recorded dustbathing behaviour was analysed using continuous behaviour and focal animal sampling. Stimulation to dustbathe was apparently stronger on UW (median 4 of 4 hens per group dustbathing) than on FW (median 3 of 4, p = 0.003), also reflected by a shorter mean latency until dustbathing behaviour occurred (UW: 17.7 min, FW: 70.1 min, p < 0.0001). Dustbathing behaviour was more pronounced on UW with more side rubbings per bout (UW: 68.9 SR/bouts, FW 39.1 SR/bout, p = 0.003) and more body/wing shakes following the bout (UW: 3.5 BWS, FW: 1.5 BWS, p < 0.0001). Therefore, under behavioural aspects wood shavings become more stimulating and adequate for dustbathing when degraded due to being used, provided that they are still friable. Under the experimental conditions, substrate depth played a smaller role, although there were interactions with substrate quality and increased vertical wing shakes on shallow substrate (S: 59.4 VWS/bout, D: 35.3 VWS/bout, p < 0.0001), possibly because it was more difficult to bring substrate into the plumage.