Rearing Enrichments Affected Ranging Behavior in Free-Range Laying Hens

Abstract

Within Australia, free-range systems are prevalent, but pullets destined for range access are reared indoors. This mismatch between rearing and layer housing may hinder adaptation to the free-range environment. Rearing enrichments could enhance pullet development. A total of 1,386 Hy-Line Brown® chicks were reared inside an experimental facility across 16 weeks with 3 enrichment treatments including (1) a control group with standard floor-housing, (2) a novelty group providing novel objects that changed weekly ("novelty" hens), and (3) a structural group with custom-designed H-shaped structures including opaque sides ("structural" hens). At 16 weeks of age, all pullets were leg-banded with microchips and moved to an experimental free-range system with 9 identical pens (n = 3/rearing treatment). From 25 to 64 weeks, individual hen daily ranging behavior was tracked via radio-frequency identification technology and grouped into 6 age periods per rearing treatment. Video footage was used to count the number of hens at different distances on the range for the first 14 days of access, and eggs were assessed for albumen corticosterone concentrations 4 days prior to (n = 450) and 1 week after first range access (n = 450). Across most age periods, the structural hens spent the most time ranging (P ≤ 0.01), the novelty hens showed the fewest number of visits to the range (P < 0.0001), and both enriched hen groups had the longest maximum visit durations (P ≤ 0.02). Range use increased with age across all treatments with only 3% of hens never going outside. All hens were initially slow to use the range area with fewer novelty hens venturing farther onto the range (P ≤ 0.03). The structural hens had higher albumen corticosterone concentrations and variance (both P ≤ 0.004) prior to range access. All hens showed an increase in albumen corticosterone following the first week of range access resulting in no differences between rearing treatments in means (P = 0.92) and variance (P = 0.63). Different enrichments have differing impacts on ranging behavior, but further research is needed to understand the mechanisms of effects, with differences in brain lateralization a potential hypothesis to be tested.

Keywords: RFID; adaptability; chicken; corticosterone; hen; individual; stress; welfare.

Figure 1

Top-down view of the indoor pen and outdoor range showing placement and dimensions of the indoor perch, nest box, water, and feed resources, the range access pop-holes, and different range substrates. Each of the nine pens had identical indoor configuration except for three pens, which had a radio-frequency identification box in the front right corner that the small nest box sat upon (the small nest boxes were elevated by cinder blocks in the remaining pens). Reproduced from (27).

Figure 2

The mean number of laying hens from three rearing enrichment treatments (control, novelty, structural) outside at increasing distances of the range length across the first 14 days of range access. Individual data points indicate daily means for each pen per rearing treatment.

Figure 3

The mean corticosterone concentrations (ng/g) of egg albumen from hens exposed to three rearing enrichment treatments (control, novelty, structural) sampled 4 days prior to and 7 days after the first range access. Box ends represent the first and third quartiles with whiskers extending to data within 1.5 x the interquartile range or upper and lower data points (excluding outliers) if the data do not reach the computed ranges. Isolated data points indicate outliers. The asterisk indicates that the structural hens significantly differed from the other treatment groups prior to the range access.

Figure 4

The mean (± SD) daily hours spent outside on the range for hens from three rearing enrichment treatments (control, novelty, structural) across hen age periods. The mean daily temperature during ranging hours is also plotted. Asterisks indicate that the structural hens differed significantly from the control and novelty hens across four of the six age periods.

Figure 5

The mean (± SD) daily visits to the outside range for hens from three rearing enrichment treatments (control, novelty, structural) across the periods of hen age (weeks). Asterisks indicate that the novelty hens differed significantly from the control and structural hens across four of the six age periods.

Figure 6

The mean maximum daily visit time outside for hens from three rearing enrichment treatments (control, novelty, structural) across the periods of hen age (weeks). Box ends represent the first and third quartiles with whiskers extending to data within 1.5 x the interquartile range or upper and lower data points (excluding outliers) if the data do not reach the computed ranges. Isolated data points indicate outliers. Asterisks indicate that the control hens differed from both enriched treatment groups across five of the six age periods.

Figure 7

The proportion of available ranging days that individual hens from three rearing treatments (control, novelty, structural) went outside across the flock cycle (25–64 weeks). Differences between treatments were found at 38–44, 47–54, and 55–64 weeks of age.

Figure 8

The proportion of available days that the hens (n = 98) spent outside across different age periods. Displayed hens were selected based on showing no days outside in the last age period (55–64 weeks). Different colors represent individual hens.