Individual variation in how hens interact with a dust substrate

This paper re-examines in further detail the findings of an experiment reported previously by Laine et al. (2009). Briefly, Laine et al. (2009) preference tested laying hens (n = 15) for their choice between social contact (a familiar, subordinate hen) and a dust substrate (a tray of peat moss) in a Y-maze apparatus. Although the dust substrate was much preferred to social contact, it was observed that hens differed in how they interacted with the dust substrate in the Y-maze when they chose it. To examine individual variation further, each hen was classified as one of three types, based on the proportion of Y-maze trials in which the hen chose the Y-maze arm containing dust and commenced a dustbathing bout. A dustbathing bout was defined as commencing when the hen first rolled onto her side. Hens which commenced a dustbathing bout on >85% of dust-chosen trials were defined as “dustbathers”, while hens which commenced a dustbathing bout on <15% of dust-chosen trials were defined as “non dustbathers”. When dust was chosen but dustbathing was not performed, hens generally used the dust substrate for foraging, specifically pecking and scratching at the dust. Of the 15 hens, 4 hens were defined as “dustbathers”, 6 were defined as “non dustbathers” while the remaining 5 hens commenced a dustbathing bout on 15-85% of dust-chosen trials. The behaviour of the hens had been video recorded for an 11-day period in the home cage prior to Y-maze testing and their dustbathing behaviour during the hour following the daily filling of the home cage dustbath was recorded. The dustbathing behaviour of “dustbathers” and “non dustbathers” was compared using a t-test. During the 11-day home cage observation period, hens defined as “dustbathers” dustbathed on a higher proportion of days (P = 0.0135) and had a shorter latency to commence dustbathing (P = 0.0043) compared to hens defined as “non dustbathers”. Moreover, “dustbathers” performed more real dustbathing bouts (i.e. dustbathing bouts incorporating the dust substrate) compared to “non dustbathers” (P = 0.0032). These results imply that individual hens differed in how they interacted with the dust substrate, but these differences were consistent between the home cage and Y-maze environments. Similar results were described in Petherick et al. (1990) who suggested that peat moss may “switch on” dustbathing for only some hens. This variation in how hens interact with a dust substrate implies that dustbathing and foraging opportunities may differ in their importance to different individuals. If this is the case, it raises the question of the relative importance of a dust substrate for these two types of hens. Potentially, the presence or absence of a dust substrate may have a differential effect on the welfare of individuals. For example, do “dustbathers” suffer more in the absence of a dustbathing substrate compared to “non dustbathers”? It also raises the question about the genetic and/or experiential basis of preferences. Further research is warranted to determine whether this effect applies to a larger population.