Relationship between Range Use and Fearfulness in Free-Range Hens from Different Rearing Enrichments

Abstract

Inconsistency between the environments of indoor pullet rearing and adult outdoor housing may increase the fearfulness in free-range hens. Rearing enrichments and/or range use may reduce adult fearfulness. Hy-Line Brown^® chicks (n = 1700) were reared inside across 16 weeks with three enrichment treatments: weekly changing novel objects, custom-designed perching/navigation structures, or no additional enrichments. Pullets were transferred to a free-range system at 16 weeks of age, with range access provided from 25 weeks. At 62 weeks, 135 hens were selected from the three rearing treatments and two ranging groups (indoor: no ranging and outdoor: daily ranging) based on individual radio-frequency identification tracking. Individual behavioural tests of tonic immobility, emergence, open field, and novel object (pen level) were carried out on hens. Spectrograms of vocalisations were analysed for the open field test, as well as computer vision tracking of hen locomotion. The results showed few effects of rearing treatments, with outdoor rangers less fearful than indoor hens. The latency to step in the open field test negatively correlated with hen feather coverage. These results show that individual variation in ranging behaviours is present even following rearing enrichment treatments, and subsequent range use might be an indicator of bird fearfulness.

Keywords: acoustic; behaviour; chicken; computer vision; emergence test; open field test; plumage; spectrogram; tonic immobility; vocalisation.

Figure 1

Automated computer tracking to show: (a) distance moved across time by a relatively active hen along the length and width of the test arena, (b) mean shape of the hen based on a superimposed ellipse, where a value of 1 is a full circle, and a value of 0.5 indicates a shape twice as long as wide, (c) distance moved across the test duration, and (d) position of the moving hen across time (parameters are described in greater detail in Table 1).

Figure 2

Automated computer tracking to show: (a) distance moved across time by a relatively stationary hen along the length and width of the test arena, (b) mean shape of the hen based on a superimposed ellipse, where a value of 1 is a full circle, and a value of 0.5 indicates a shape twice as long as wide, (c) distance moved across the test duration, and (d) position of the stationary hen across time (parameters are described in greater detail in Table 1).

Figure 3

The mean ± SEM of the number of vocalisations produced across time in the open field test (0 to 1 min, 1 to 2 min, 2 to 3 min, 3 to 4 min, and 4 to 5 min) by hens of different ranging patterns (indoor and outdoor). ^a–d Dissimilar superscript letters indicate significant differences between the ranging patterns across time (p < 0.005). Raw values are presented, with the analyses conducted on the transformed data.

Figure 4

The mean ± SEM of the number of steps made in the open field test across time (0 to 1 min, 1 to 2 min, 2 to 3 min, 3 to 4 min, and 4 to 5 min) by hens of different ranging patterns (indoor and outdoor). ^a–d Dissimilar superscript letters indicate significant differences between the ranging patterns across time (p < 0.005). Raw values are presented, with the analyses conducted on the transformed data.