Working for food is related to range use in free-range broiler chickens

Abstract

When animals prefer to make efforts to obtain food instead of acquiring it from freely available sources, they exhibit what is called contrafreeloading. Recently, individual differences in behavior, such as exploration, were shown to be linked to how prone an individual may be to contrafreeload. In this work, our main objective was to test whether and how individual differences in range use of free-range broiler chickens (Gallus gallus domesticus) were related to the individual motivation to contrafreeload. We also verified whether other behavioral variations could relate to range use. To that aim, over three different periods (before range access, first weeks of range access, and last weeks of range access), chickens with different ranging levels (low and high rangers) were submitted to a contrafreeloading test and had different behaviors recorded (such as foraging, resting, locomotion) in their home environment. During the contrafreeloading test, chickens were conditioned to one chamber presenting a foraging substrate and mealworms, while in the other chamber, mealworms were freely available on the floor. During testing trials, chickens had access to both empty chambers, and the time spent in each chamber was quantified. On average, low rangers preferred the chamber where mealworms were easily accessible (without the foraging substrate), while high rangers preferred the chamber where mealworms were accessible with difficulty, showing greater contrafreeloading. Out of ten behaviors recorded in chickens' home environment, foraging was the only one that differed significantly between our two ranging groups, with low rangers foraging, on average, significantly less than high rangers. These results corroborate previous experiences suggesting that range use is probably linked to chickens' exploratory trait and suggest that individual differences in free-range broiler chickens are present even before range access. Increasing our knowledge of individual particularities is a necessary step to improve free-range chicken welfare on the farm.

Figure 1

Schedule of the behavioral observations (Continuous sampling, CS, n = 58), Ranging behavior measurements (RB, n = 117), and contrafreeloading tests (CFL, n = 58) made during the production cycle of free-range chickens.

Figure 2

Side view of the arena (compartments and dimensions) used during the contrafreeloading conditioned place preference task (CPP). All over the task, and for all periods of testing, the extremes of each chamber were fenced to house two flockmate chickens (not tested). Chickens were always placed in the center of each chamber (conditioning, dark arrows) or the center of the apparatus when the wall was not present (test, dark circle).

Figure 3

Percentage of time spent in foraging behavior averaged over three different periods of the production cycle (Period 1: before range access, Periods 2 and 3: after range access), for low (N = 19) and high ranger chickens (N = 21). *Differences between ranging groups at p < 0.05 (LMM Test). Data are presented as mean ± s.e.

Figure 4

Preference index (PI) during a conditioned place preference task, averaged over three different periods of the production cycle (Period 1: before range access, Periods 2 and 3: after range access), for low (N = 19) and high ranger chickens (N = 21). The PI varied between 1.0 and 1.0. Positive values indicate a preference for the chamber with the foraging substrate, while negative values indicate a preference for the chamber where mealworms were freely disposed of on the ground. *Differences between ranging groups at p < 0.05 (LMM Test). Data are presented as mean ± s.e.