The development of laying hen locomotion in 3D space is affected by early environmental complexity and genetic strain

Abstract

Adult laying hens are increasingly housed in spatially complex systems, e.g., non-cage aviaries, where locomotion between elevated structures can be challenging for these gallinaceous birds. This study assessed the effect of early environmental complexity on spatial skills in two genetic strains. Brown (B) and white (W) feathered birds were raised in: Conventional cages with minimal complexity (Conv) or rearing aviaries with low (Low), intermediate (Mid), or high complexity (High). Birds from each housing treatment were challenged at three different time points in three different, age-appropriate vertical spatial tasks. Whites performed better than brown birds in all tests regardless of rearing environment. In chicks, test performance was predominantly explained by variation between replicates and differences in motivation for test participation. Treatment effects were seen in pubertal birds (pullets), with pullets from aviaries performing better than those from Conv. White High pullets performed better than white Mid or Low, an effect that was not found in browns. Pullets preferred to use a ramp to move downwards, but only when ramps had previously been experienced and when the ramp was not too steep. Overall, early environmental complexity affected spatial skills of laying hen pullets with stronger effects in white than brown feathered birds.

Figure 1

Photos of the different housing systems. The left side illustrates the brooding period (first six weeks) and the right column shows the open period (six-17 weeks). The location of perches and platforms are indicated for the brooding period only. Environmental complexity increased from top to bottom. The Figure was created using Microsoft PowerPoint for Microsoft 365 MSO version 2304.

Figure 2

(A) A photo of a brown chick being tested in set up 4.1 (lowest hurdle). (B) Top view of the testing arena (200 × 170 cm). Section ‘1’ contained the test bird, the start location is indicated by the red X (70–80 cm from the hurdle). Section ‘2’ contained the group of birds intended for social incentive (120 × 170 cm). A wire fence ‘3’ (45 cm from the hurdle at the farthest point) kept the chicks in the social group from jumping into the testing section. ‘1’ and ‘2’ were divided by a solid wall with the plastic grid hurdle ‘4’ (55 cm long) in the centre. (C) Front view of the hurdles with different difficulty levels; ‘4.1’ 30 cm tall, ‘4.2’ 45 cm + 90 cm ramp, ‘4.3’ 45 cm tall, ‘4.4’ 60 cm + 90 cm ramp, and ‘4.5’ 60 cm tall. (D) A photo of a white chick being tested in set up 4.4 (tallest hurdle + ramp). Schematics were created using Microsoft PowerPoint for Microsoft 365 MSO version 2304.

Figure 3

(A) A photo of a pullet during task 3 of the vertical navigation test. (B) Test pen of the vertical navigation test. Platforms were at 60 cm, 120 cm, and 180 cm height. During habituation (H), platforms were made inaccessible with a white plastic over (dashed line) and reward dish (red, mealworms and sweet corn) placed on the floor. For tasks 1 to 4, hens were placed on the floor, facing away from the reward dish. In task 5, hens were placed on the topmost platform, facing away from the reward. In tasks 2 and 4, success was defined as the hen reaching the highest reward with the lower dishes drawing the attention upwards but holding very little food. Schematics were created using Microsoft PowerPoint for Microsoft 365 MSO version 2304.

Figure 4

Test pen of the ramp-choice test. Ramps connected to the platforms at 60 cm and 120 cm at a 27° or 48° angle respectively. For tasks 60U, hens were placed on the floor, facing away from the reward dish (red). In tasks 60D and 120D, hens were placed on the platform, facing away from the reward. In each test, hens had the choice to navigate by aerial locomotion, by using the ramp or by a mix of both. Schematics were created using Microsoft PowerPoint for Microsoft 365 MSO version 2304.

Figure 5

The probability of successful hurdle crossing (A) and measures of motivation for social re-instatement (B–D). (A) Estimated probability of success, (B) latency in seconds to start walking and (C) frequency of vocalisation bouts for each treatment group. Brown chicks are in circles (red) and white chicks in triangles (blue). (D) Persistence; the number of crossing attempts per test depending on success. Successful brown chicks are in squares (red), unsuccessful browns in circles (red), successful whites in triangles (blue), and unsuccessful whites in diamonds (blue). The rearing treatments are on the X-axis are in order of increasing spatial complexity; conventional cages [Conv], aviary with low [Low], intermediate [Mid], or high [High] complexity. The Y-axis reflects the estimated mean ± standard error. Different letters indicate a statistical difference according to the post-hoc analysis. Graphs were created using R and R Studio version 3.5.2.

Figure 6

Probability of success in the vertical navigation test (all 5 tasks combined) according to housing system. The probability was affected by (A) a housing by strain interaction where browns are in brown and whites in blue (patterned) and (B) a housing by jumping direction interaction with upwards tasks (tasks 1–4) in black (patterned) and the downward task (task 5) in grey. Different letters indicate a statistical difference according to the post-hoc analysis. Graphs were created using Microsoft Excel for Microsoft 365 MSO version 2304.

Figure 7

Locomotion strategy used in the ramp-choice test as percentage of observations. The different strategies are aerial locomotion, a combination of aerial and ramp use (mixed), or exclusive use of the ramp. The different bands represent the proportion of pullets from each treatment group with housing complexity increasing from the bottom bands to the top bands (dark to bright colours). Data includes all attempted transitions regardless of success. (A) Task 60U (up 60 cm): 55.68% of pullets used aerial locomotion, 18% used a mix of aerial and the ramp, and 26.32% exclusively used the ramp. Strategy was dependent on housing and strain (Cochran–Mantel–Haenszel [CMH] M² = 7.8, p = 0.02), brown birds in tan-scale, whites in grey-scale). (B) Task 60D (down 60 cm): 27.97% of pullets used aerial locomotion, 22.99% used a mix, and 49.04% used the ramp only. Strategy was independent on housing but not strain (housing × strain: CMH M² = 4.1, p = 0.1; housing: chi-square [χ²] contribution to aerial: Conv χ² = 8.8, Low χ² = 0.03, Mid χ² = 1, High χ² = 0.9, ramp: Conv χ² = 0.1, Low χ² = 0.7, Mid χ² = 0.6, High χ² = 0.04, mixed: Conv χ² = 4, Low χ² = 0.2, Mid χ² = 0.04, High χ² = 0.3). Graphs were created using R and R Studio version 3.5.2.