Domestic hen chicks’ conditioned place preferences for sound

Affective trajectories: Are hens influenced by positive and negative changes in their living conditions?

Most studies of the effects of housing and husbandry on animals' affective states and welfare investigate the impact of stable living conditions, comparing for example, animals living in enriched environments with those living in non-enriched ones. Changes in living conditions, including from more to less enriched environments, have also been found to have effects on measures of affective state and welfare in some species. But these studies have not investigated whether it is the trajectory of change that has affected the animals (e.g., worsening conditions), or simply the nature of their final environment (e.g., non-enriched). Here, we hypothesised that laying hens living in worsening conditions across a six-week period (gradually moving from preferred to non-preferred living conditions; "Trajectory to Non-Preferred", TNP, n = 30), would show evidence of more negative affective states and poorer welfare than those living continuously in non-preferred conditions for the same duration ("Stable Non-Preferred", SNP, n = 30). We also hypothesised that hens living in improving conditions (gradually moving from non-preferred to preferred living conditions; "Trajectory to Preferred", TP, n = 30), would show evidence of more positive affective states and better welfare than those living continuously in preferred conditions ("Stable Preferred", SP, n = 30). The preferred living condition provided extensive resources and intermittent rewarding events (such as the delivery of food treats) known to be valued and preferred by most hens, while the non-preferred living condition provided just basic resources and intermittent aversive events (e.g., loud noises). The hens' affective states and welfare were measured using home-pen behavioural observations, body condition assessments, physiological stress measures (e.g., blood corticosterone, glucose, etc.), physical challenge tests, and judgement bias tests. A number of differences between hens in the trajectory and stable living conditions were found: TP hens were lighter, showed more foraging behaviour and less standing alert and head-shaking than SP hens, while TNP hens showed more head-shaking, mild feather pecking and aggressive attacking of pen mates than SNP hens. However, some of these differences failed to reach significance following Benjamini adjustments for multiple testing. The groups also did not differ in their judgement biases (measured in a sub-sample of 12 hens per experimental group), response to physical challenges, or measures of physiological stress. We conclude that the hens in the present study showed some evidence of responsiveness to 'affective trajectories' in their living conditions, but no definitive effects on their affective states and welfare.

Selection for reduced fear in red junglefowl changes brain composition and affects fear memory

Brain size reduction is a common trait in domesticated species when compared to wild conspecifics. This reduction can happen through changes in individual brain regions as a response to selection on specific behaviours. We selected red junglefowl for 10 generations for diverging levels of fear towards humans and measured brain size and composition as well as habituation learning and conditioned place preference learning in young chicks. Brain size relative to body size as well as brainstem region size relative to whole brain size were significantly smaller in chicks selected for low fear of humans compared to chicks selected for high fear of humans. However, when including allometric effects in the model, these differences disappear but a tendency towards larger cerebra in low-fear chickens remains. Low-fear line chicks habituated more effectively to a fearful stimulus with prior experience of that same stimulus, whereas high-fear line chicks with previous experience of the stimulus had a response similar to naive chicks. The phenotypical changes are in line with previously described effects of domestication.

Examining affective structure in chickens: valence, intensity, persistence and generalization measured using a Conditioned Place Preference Test

When measuring animals' valenced behavioural responses to stimuli, the Conditioned Place Preference (CPP) test goes a step further than many approach-based and avoidance-based tests by establishing whether a learned preference for, or aversion to, the location in which the stimulus was encountered can be generated. We designed a novel, four-chambered CPP test to extend the capability of the usual CPP paradigm to provide information on four key features of animals' affective responses: valence, scale, persistence and generalization. Using this test, we investigated the affective responses of domestic chickens (Gallus gallus domesticus) to four potentially aversive stimuli: 1. Puffs of air; 2. Sight of (robotic) snake; 3. Sprays of water; 4. Sound of conspecific alarm calls. We found conditioned avoidance of locations associated with the air puffs and water sprays (Friedman's χ2 (3) = 13.323 p > .005; χ2 (3) = 14.235 p > .005), but not with the snake and alarm calls. The scale of the learned avoidance was similar for the air puff and water spray stimuli, but persistence and generalization differed. We conclude that the four chambered CPP test can have a valuable role to play in making multi-feature measurements of stimulus-generated affective responses, and we highlight the value of such measurements for improving our understanding of the structure of affect in chickens and other animals.