Elsevier

Physiology & Behavior

Volume 133, 22 June 2014, Pages 161-169
Physiology & Behavior

Domestication effects on behavioural and hormonal responses to acute stress in chickens

https://doi.org/10.1016/j.physbeh.2014.05.024Get rights and content

Highlights

  • Behaviour reactions to restraint were stronger in Red Junglefowl than in domestic chickens.

  • Red Junglefowl had stronger corticosterone reaction than domestic birds.

  • Both behaviour and steroid levels recovered faster in Red Junglefowl.

  • Domestication may have modified stress responses in chickens.

Abstract

Comparative studies have shown that alterations in physiology, morphology and behaviour have arisen due to the domestication. A driving factor behind many of the changes could be a shift in stress responses, with modified endocrine and behavioural profiles. In the present study we compared two breeds of chicken (Gallus gallus), the domestic White Leghorn (WL) egg laying breed and its ancestor, the Red Junglefowl (RJF). Birds were exposed to an acute stress event, invoked by 3 or 10 min of physical restraint. They were then continuously monitored for the effects on a wide range of behaviours during a 60 min recovery phase. Blood samples were collected from the chicken at baseline, and after 10 and 60 min following a similar restraint stress, and the samples were analyzed for nine endogenous steroids of the HPA and HPG axes. Concentration of the steroids was determined using validated liquid chromatography tandem mass spectrometry methods. In RJF, an immediate behavioural response was observed after release from restraint in several behaviours, with a relatively fast return to baseline within 1 h. In WL, some behaviours were affected for a longer period of time, and others not at all. Concentrations of corticosterone increased more in RJF, but returned faster to baseline compared to WL. A range of baseline levels for HPG-related steroids differed between the breeds, and they were generally more affected by the stress in WL than in RJF. In conclusion, RJF reacted stronger both behaviourally and physiologically to the restraint stress, but also recovered faster. This would appear to be adaptive under natural conditions, whereas the stress recovery of domesticated birds has been altered by domestication and breeding for increased reproductive output.

Introduction

Domesticated animals have evolved for thousands of years in a relatively protected environment compared to the original natural habitat, with reduced predator pressure, protection from disease and regular food supply. However, other potential stressors have replaced the natural ones, such as crowding [1], [2], human presence and handling [3], [4], [5], [6], artificial light [7] and lack of out-door space. The stressors affecting domestic animals in the human-controlled environment are therefore different than for the wild ancestors, and the ability and strategy to cope with various types of stressors may have been modified during domestication [8].

It has been suggested that modifications in the stress response system may have been a driving force behind the numerous changes in morphology, physiology and behaviour seen in domesticates [9], [10]. In the present study, we compare stress recovery patterns between the Red Junglefowl (RJF), which is the main ancestor of all domestic chicken breeds [11], [12] and a domesticated egg-laying strain, the White Leghorn (WL). RJF is known to show more fearful behaviour in a range of test situations [13], and several behaviour differences have also been described in foraging strategies and exploration patterns [14], [15], [16].

A central aspect of stress is the endocrinological response of the individual. Steroid hormones pass the blood brain barriers and act on the brain by modulation of gene expression [17] or through non genomic pathways such as modification of GABA receptor function [18]. Various studies have compared hypothalamic–pituitary–adrenal (HPA) axis reactivity of wild and domesticated animals and they suggest that attenuated HPA-axis reactivity in domesticates is common in many species including mice [19], rats [20], pigs [21], guinea pigs [10] silver foxes [22], mallard ducks [23] and salmonids [24]. Furthermore, activation of the HPA-axis suppresses the hypothalamic–pituitary–gonadal (HPG) axis in most animals through several mechanisms [25]. For instance, corticotropin releasing factor (CRF) inhibits secretion of gonadotropin releasing hormone (GnRH), while glucocorticoids suppress secretion of pituitary luteinizing hormone (LH), as well as progesterone and oestrogens from ovaries [26]. In general stress limits the efficiency of reproduction and causes economic loss to the farm. However, in contrast to the HPA-axis, the influences of domestication on the stress related function of the HPG-axis have not been explored thoroughly in any species. Some acute events, in addition to physical restraint, have been shown to induce a stress response in chickens, for example heat stress [27], [28], [29] and unpredictable light regimes [30]. Restraint stress however is a well-established method for triggering a stress response in chickens (see for example [29], [31], [32]) where also the HPA-axis recovery has been investigated [31].

We used detailed behavioural comparisons of the behaviour of domestic chickens and their ancestors during recovery from an acute stress experience, combined with a uniquely broad assessment of changes in an array of steroid hormones. This allowed us, for the first time, to assess the effects of domestication on behavioural and endocrine stress responses in chickens. In particular, we focused on the recovery process and the return to normal levels of both behaviour and concentrations of the steroids, using a similar approach as in earlier research on stress recovery [33], [34], [35], [36], [37], [38], [39], [40].

Hence, the aims of this study were to integrate a comprehensive picture of behavioural and endocrine (steroid) responses during recovery from an acute stress experience in chickens, and to compare the response between domesticated chickens and their wild ancestors.

Section snippets

Ethical statement

The project was approved by the Linköping Council for Ethical Licensing of Animal Experiments; ethical permit no 122-10.

Birds and housing

In total 71 birds, of which 25 males and 46 females were tested. Half the birds were domesticated White Leghorn (WL) and the other half were ancestral Red Junglefowl (RJF). The RJF population in the current study originates from a wild caught group of animals from Thailand, maintained in our research facilities for about 10 generations. Carefully supervised pedigree breeding

Behaviour

Baseline values (Table 2) differed significantly between the breeds for “alert behaviour”, “feather ruffle” and “crowing” which were more frequent in WL, while “relaxed behaviour” and “preen” were more frequent in RFJ. WL tended to “ground peck” more than RJF. Females showed higher baseline of “relaxed behaviour” and males displayed higher baseline levels of “feather ruffle”. A significant sex × breed effect was seen in “drinking” and “wing flap”, which both were performed the most by RJF males

Discussion

Both Red Junglefowl (RJF) and the domesticated White Leghorn (WL) layers showed an immediate response to the restraint stress, as evident from behaviour as well as endocrine changes. The reactions of the ancestral breed were more acute, with a pronounced behavioural reaction and a significant increase in corticosterone levels, whilst the recovery was slower and the overall responses sustained for a longer period in the domesticated birds. This shows that the stress response and recovery process

Acknowledgements

The project was supported by grants from the Swedish Research Council (VR) 621-2011-4731, the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS) 221-2011-1088, and ERC (project Genewell 322206), and within the auspice of the Swedish Centre of Excellence in Animal Welfare. For excellent technical assistance we thank Lejla Bektic. We thank ARUP Institute for Clinical and Experimental Pathology for supporting this project.

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