Effect of Environmental Complexity and Stocking Density on Fear and Anxiety in Broiler Chickens.

Mallory G Anderson,Ruth C Newberry,Andrew M Campbell,Andrew Crump,Gareth Arnott,Leonie Jacobs

doi:10.3390/ani11082383

Abstract

Simple SummaryBroiler chickens are conventionally housed in monotonous environments at high stocking densities, which can negatively affect their welfare. This study evaluated the impact of environmental complexity and stocking density on anxiety and fear in broilers. Through behavioral testing, we found that broilers housed at higher densities responded less fearfully than those housed at the lower density, which is contradicting to expectations and previous research. Broilers housed in complex environments exhibited responses consistent with reduced anxiety compared to broilers housed in monotonous environments, suggesting improved welfare for broilers housed in the complex environment.Barren housing and high stocking densities may contribute to negative affective states in broiler chickens, reducing their welfare. We investigated the effects of environmental complexity and stocking density on broilers’ attention bias (measure of anxiety) and tonic immobility (measure of fear). In Experiment 1, individual birds were tested for attention bias (n = 60) and in Experiment 2, groups of three birds were tested (n = 144). Tonic immobility testing was performed on days 12 and 26 (n = 36) in Experiment 1, and on day 19 (n = 72) in Experiment 2. In Experiment 1, no differences were observed in the attention bias test. In Experiment 2, birds from high-complexity pens began feeding faster and more birds resumed feeding than from low-complexity pens following playback of an alarm call, suggesting that birds housed in the complex environment were less anxious. Furthermore, birds housed in high-density or high-complexity pens had shorter tonic immobility durations on day 12 compared to day 26 in Experiment 1. In Experiment 2, birds from high-density pens had shorter tonic immobility durations than birds housed in low-density pens, which is contrary to expectations. Our results suggest that birds at 3 weeks of age were less fearful under high stocking density conditions than low density conditions. In addition, results indicated that the complex environment improved welfare of broilers through reduced anxiety.

Highlights

Environmental enrichment can be defined as “a modification of the environment of captive animals, thereby increasing the animal’s behavioral possibilities and leading to improvements of their biological function” [1]
Another study found that broilers housed at a high stocking density of 56 kg/m2 showed longer tonic immobility (TI) durations than broilers housed at lower densities [33]. Two of these lower stocking densities were comparable to the high and low densities at the time of TI testing in our study (6 kg/m2 and 15 kg/m2 compared to 8–16 kg/m2 and 4–8 kg/m2 at testing age in the present study), yet they did not find differences in TI duration between those two density levels (112 s for birds housed at 6 kg/m2 versus 101 s for birds housed at 15 kg/m2), whereas the present study found that birds from HD pens had shorter TI durations compared to birds from LD pens
We investigated the effects of housing broiler chickens in a high- or low-complexity environment under high or low stocking densities on their level of fear and anxiety

Summary

Introduction

Environmental enrichment can be defined as “a modification of the environment of captive animals, thereby increasing the animal’s behavioral possibilities and leading to improvements of their biological function” [1]. Fear is a short-term emotional response motivating flight from, or freezing in response to, a currently present, immediate threat to survival, while anxiety is a longer-term emotional response motivating vigilance (i.e., alertness) in response to perceived potential threat and is amplified by adverse pre-and postnatal life experiences [5,7,8,9,10]. These systems have evolved as adaptive mechanisms promoting survival in dangerous situations through temporary activation of sympathetic and hypothalamic-pituitary-adrenal axis activity and suspension of growth-promoting parasympathetic activity [5]. A TI test could provide valuable insight into broiler fear levels when handled after rearing in environments varying in complexity and stocking density

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