Associations of range use with individual behaviour, clinical welfare indicators, fear response and gastrointestinal characteristics of two laying hen hybrids

Abstract

Access to an outdoor range provides laying hens with increased space and improved opportunities for performing natural behaviours. However, not all hens utilise the range to the same extent, and this may be associated with the welfare of the individual hen. The aim of this study was to assess if extent of range use was associated with several clinical welfare indicators, time budgets, measures of tonic immobility and gastrointestinal characteristics. One hundred twenty focal individuals (Bovans Brown, n = 60; Dekalb White, n = 60) randomly chosen from 12 pens of 100 hens (10 hens from each pen) were housed in accordance with the EU organic standards. Clinical welfare indicators including plumage condition, foot health, keel bone damage and body weight were assessed upon arrival at 18 weeks of age and again at 23, 28, 33 and 38 weeks of age. Over five three-day periods at corresponding weeks, hens received individual back marks for identification and behaviour was recorded by instantaneous scan sampling from 8:30–15:30 in the house and on the range. Behaviour recorded included comfort behaviours, drinking, dust bathing, eating, foraging, locomotion, nest use, pecking, perching, resting and standing. Frequency of passes through the pophole and duration of time outdoors were also determined through video observations. At 18 weeks of age a tonic immobility test was performed and number of inductions, latency to first head movement after induction and the duration of tonic immobility were recorded. At the end of the study (38 weeks of age), gastrointestinal tract morphology and contents were assessed. Individual range use varied, with hens differing in time spent on range, number of exits and consistency in these measures over time. Extent of range use was not associated with clinical welfare indicators nor fear levels as assessed by a tonic immobility test. Hens’ time budgets differed depending on where they spent most of their day, with hens utilising the range to a greater extent generally being more active (duration on range: foraging: P < 0.001, standing: P = 0.005; number of exits: locomotion: P < 0.001). Hens that utilised the range to a greater extent likely consumed more forage, as evident by the greater weight of pasture found in their crop and gizzard (P < 0.001), contributing to more developed gastrointestinal organs including the crop (duration on range: P = 0.004), gizzard (P < 0.001), and proventriculus (duration on range: P = 0.014). To conclude, the fear level and clinical welfare condition of the hens were not associated with extent of range use, unlike the time budgets and gastrointestinal characteristics.