Environmental complexity: A buffer against stress in the domestic chick.

Arda Yildirim,Irene Campderrich,Linda J Keeling,Anette Wichman,Franco Nicolas Nazar,Raul Hector Marin,Inma Estevez

doi:10.1371/journal.pone.0210270

Abstract

Birds kept in commercial production systems can be exposed to multiple stressors from early life and this alters the development of different morphological, immunological and behavioural indicators. We explore the hypothesis that provision of a complex environment during early life, better prepares birds to cope with stressful events as well as buffers them against future unpredictable stressful episodes. In this study, 96 one day old pullets were randomly distributed in eight pens (12 birds/pen). Half of the chicks (N = 48) were assigned to a Complex Environment (CENV: with perches, a dark brooder etc.) the others to a Simple Environment (SENV: without enrichment features). Half of the birds from each of these treatments were assigned to a No Stress (NSTR, 33°C) or to an acute Cold Stress (CSTR, 18–20°C) treatment during six hours on their second day of life. At four weeks of age, chicks with these four different backgrounds were exposed to an Intermittent Stressful Challenges Protocol (ISCP). In an immunological test indicative of pro-inflammatory status Phytohemagglutinin-P (PHA-P), the response of CSTR birds was ameliorated by rearing chicks in a CENV as they had a similar response to NSTR chicks and a significantly better pro-inflammatory response than those CSTR birds reared in a SENV (five days after the CSTR treatment was applied). A similar better response when coping with new challenges (the ISCP) was observed in birds reared in a CENV compared to those from a SENV. Birds reared in the CENV had a lower heterophil/lymphocyte ratio after the ISCP than birds reared in SENV, independently of whether or not they had been exposed to CSTR early in life. No effects of stress on general behaviour were detected, however, the provision of a CENV increased resting behaviour, which may have favoured stress recover. Additionally, we found that exposure to cold stress at an early age might have rendered birds more vulnerable to future stressful events. CSTR birds had lower humoral immune responses (sheep red blood cells induced antibodies) after the ISCP and started using elevated structures in the CENV later compared to their NSTR conspecifics. Our study reflects the importance of the early provision of a CENV in commercial conditions to reduce negative stress-related effects. Within the context of the theory of adaptive plasticity, our results suggest that the early experience of the birds had long lasting effects on the modulation of their phenotypes.

Highlights

Birds used in poultry production systems can be exposed to multiple stressors early in life such as hatching without maternal contact, transport, heat or cold environmental temperature [1,2,3]
After exposure to the Intermittent Stressful Challenges Protocol (ISCP) (28 day old chicks-T3) we found a significant increase in H/L ratio, but only for birds reared in a Simple Environment (SENV) and independently of whether they had been exposed to Cold stress (CSTR) early in life (Fig 7)
This study demonstrates that environmental complexity during rearing may help to ameliorate the consequences of early stressful events, but may help birds to cope better with future challenges

Summary

Introduction

Birds used in poultry production systems can be exposed to multiple stressors early in life such as hatching without maternal contact, transport, heat or cold environmental temperature [1,2,3]. Understanding the impact that these early stressors have on the birds’ behaviour and physiology is important from an animal welfare perspective and could, at the same time, elucidate the evolution of phenotypic diversity in populations [4] In this context, the adaptive plasticity theory proposes that some of the inputs animals receive during their development, perhaps the stressors to which they are submitted or the conditions of their rearing environment, are factors capable of producing lasting alterations. The adaptive plasticity theory proposes that some of the inputs animals receive during their development, perhaps the stressors to which they are submitted or the conditions of their rearing environment, are factors capable of producing lasting alterations These alterations may, in turn, lead to the development of a certain phenotype that could be adaptive for the individuals future life. It can result in the development of a phenotype with deleterious effects on fitness, perhaps making individuals more sensitive to future stressful conditions [5]

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Conclusion