Acute stress enhances sensitivity to a highly attractive food reward without affecting judgement bias in laying hens
Publication Type: |
Journal Article |
Year of Publication: |
2015 |
Authors: |
Carlos E. Hernandez, Geoff Hinch, Jim Lea, Drewe Ferguson, Caroline Lee |
Publication/Journal: |
Applied Animal Behaviour Science |
Keywords: |
affective states, judgement bias, poultry, reward sensitivity, stress |
ISBN: |
0168-1591 |
Abstract:
Affective states can be evaluated by assessing shifts in the animal’s expectation of a positive and negative outcome in response to ambiguous cues, also known as judgement bias (JB). The aim of this study was to use a JB methodology, using a go/go type of task where animals are required to make an active choice, to assess the effects of acute stress on affective states in hens. Thirty ISA-Brown hens were trained in a two-choice (left–right) test in an arena to associate a high-value (H) reward (four mealworms) with a 100% black and a low-value (L) reward (one mealworm) with 5% black (visually white) cues. Twenty hens that learnt the tasks were randomly allocated to either a control (C) or stress (S; 5 min social isolation in a novel environment) group. During testing, hens were presented with H and L (rewarded) and three novel ambiguous (un-rewarded) cues: 75%, 50% and 25% black. Order of cue presentation was balanced between treatments to either having ambiguous cues always preceded by L cues (L-Ambiguous) or by H cues (H-Ambiguous). Latency to approach a reward and active choice made (i.e. reaching side associated with either H or L reward) were recorded. Data are log-transformed least square mean (LSmean) latencies(s) ± SEM with back-transformed LSmean in parentheses. Latency data showed that S-hens were faster to approach a reward cue than C-hens (S 0.8 (2.3) ± 0.04 vs C 0.9 (2.6) ± 0.04 (s), P < 0.05). Hens were faster to approach H and 75% than 25% and L cues (H = 0.7 (2.0) ± 0.04 and 75% = 0.7 (2.0) ± 0.07 (s) vs 25% = 1.1 (2.9) ± 0.07 and L = 1.1 (3.1) ± 0.04 (s), P < 0.05) with intermediate responses to 50% cues (50% = 0.8 (2.3) ± 0.07 (s)). S-hens were faster to approach ambiguous cues preceded by an H reward compared to C-hens (S H-Ambiguous = 0.7 (1.9) ± 0.06, S L-Ambiguous = 1.0 (2.7) ± 0.06, C H-Ambiguous = 0.9 (2.4) ± 0.06 and C L-Ambiguous = 1.0 (2.7) ± 0.06 (s), P < 0.05). Active choice was not affected by treatment. These results show that acute stress enhances sensitivity to a previously rewarding outcome without affecting judgement bias in laying hens. Hens are sensitive to events occurring immediately before the test and the order in which cues are presented and these issues should be considered in future studies.