Environmental change or choice during early rearing improves behavioural adaptability in laying hen chicks

Abstract

Laying hens are typically moved to a novel environment after rearing, requiring adaptability to cope with change. We hypothesized that the standard rearing of laying hen chicks, in non-changing environments with limited choices (a single variant of each resource), impairs their ability to learn new routines, use new equipment and exploit new resources. On the contrary, rearing in a changing environment that also offers a choice of resource variants could better prepare chicks for the unexpected. To explore this hypothesis, environmental change and choice were manipulated in a 2 × 2 factorial experiment. Compared to standard rearing, greater change during early rearing, through repeatedly swapping litter and perch types, reduced initial freezing when exposed to a novel environment suggesting a lower fear response. Greater choice during rearing, through simultaneous access to multiple litter and perch types, resulted in shorter latencies to solve a detour task, more movement in novel environments and less spatial clustering, suggesting improved spatial skills and higher exploration. However, combining both change and choice did not generally result in greater improvement relative to providing one or the other alone. We conclude that environmental change and choice during rearing have different positive but non-synergistic effects on later adaptability potential.

Figure 1

Four treatments varying in levels of environmental change (Non-changing/Changing) and choice (Single/Multi). They represent two different types of stimulation (Change or choice) intended to manipulate experienced predictability and controllability, respectively. The 2 × 2 factorial design allowed us to explore the effects of change and choice during rearing on the welfare of laying hen chicks and their behavioural adaptability in novel situations. The combination of a Non-changing and Single-choice environment (bottom left quadrant) was considered to represent the standard rearing condition.

Figure 2

Treatment differences in the rearing pens under undisturbed conditions were found for (a) spatial clustering, calculated as the estimated marginal mean (emmean) ± SE proportion of chicks at the same resource location per instantaneous scan and (b) emmean ± SE number of chicks sparring per minute per pen. The treatment combinations were the standard rearing condition Non-changing*Single-choice (white), Non-changing*Multi-choice (blue), Changing*Single-choice (yellow), and Changing*Multi-choice (blue and yellow). Treatments with no letter in common, a or b, were significantly different (P ≤ 0.05).

Figure 3

Treatment differences in the rearing pens following disturbance were found in the emmean ± SE proportion of chicks/scan that showed (a) spatial clustering (calculated as the proportion of chicks at the same location per instantaneous scan), (b) preening, (c) foraging, (d) moving and (e) behavioural synchronization (calculated as the proportion of chicks performing the same behaviour per instantaneous scan). The treatment combinations were the standard rearing condition Non-changing*Single-choice (white), Non-changing*Multi-choice (blue), Changing*Single-choice (yellow), and Changing*Multi-choice (blue and yellow). Disturbed observations were carried out in the first 4 h after changes were made in Changing pens (and the equivalent period in Non-changing pens). Treatments with no letter in common, a or b, were significantly different (P ≤ 0.05).

Figure 4

Treatment differences found in the novelty challenge tests. In the Novel pen, a treatment effect was found for (a) proportion of chicks moving per instantaneous scan. In the Multivariate behavioural test, treatment effects were found for all behaviour measures, including (b) duration of freezing behaviour, (c) time to exit the start box by solving the detour task, and (d) number of lines crossed during a 5-min period in the open arena (see Fig. 6b). The treatment combinations were the standard rearing condition Non-changing*Single-choice (white), Non-changing*Multi-choice (blue), Changing*Single-choice (yellow), and Changing*Multi-choice (blue and yellow). Values presented are emmeans ± SE. Treatments with no letter in common, a or b, were significantly different (P ≤ 0.05).

Figure 5

Each pen (N = 16) had four different locations for litter (coloured quadrants) and perches (shaped lines). Choice was created by varying the number of litter and perch types present in the pen, where (a) Multi-choice pens had different types of litter and perches placed in each of the four locations in the pen, while (b) the Single-choice pens had the same type of litter and perch in all four locations. The effect of specific litter and perch types was controlled by balancing the litter and perch types across locations in the Multi-choice pens and across pens in the Single-choice treatment. Change involved (c) rotation of the litter and perch type locations within Multi-choice pens or (d) exchange of one type of litter and perch to another type within Single-choice pens, according to a balanced design. Change occurred three times weekly in Changing pens.

Figure 6

Chicks’ behavioural adaptability was investigated in two novelty challenges, (a) a Novel pen and (b) a Multivariate behavioural test. In the Novel pen, chicks were tested in familiar groups of ten following a transition to a novel pen (1.15 × 1.5 m) with novel resources or novel ways of presenting resources. These were a novel water container, a novel feed platform, two novel litter types (crushed straw pellets and ripped toilet paper) and four novel perch types (plastic mushroom shaped, thin rope, round wood, and a suspended piece of fabric). The pen had a concrete floor and walls covered with paper. In the Multivariate behavioural test, a chick had to first solve a detour task, as she could initially only see her pen mates through a wire net in the detour box (30 × 15 × 28 cm), and find her way out of the start box (55 × 55 × 50 cm) crossing the imaginary red line, to reunite with two pen mates (housed in the companion cage 30 × 50 × 35 cm) in the open arena (170 cm in diameter). The open arena had cardboard partitions that blocked the view of the companion cage. All flooring was covered with an unfamiliar litter type, hemp shavings. The whole test arena was covered with white net material.