Environmental complexity: A buffer against stress in the domestic chick

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.

Relationship between Range Use and Fearfulness in Free-Range Hens from Different Rearing Enrichments

“…Several studies have demonstrated reduced fearfulness in hens exposed to increased environmental complexity during rearing [ 25 , 26 , 27 , 28 ], including reduced fear when reared with perches in broiler breeders [ 29 ]. These early life experiences may act via desensitising the pullets to variable stimuli, increasing the exploration of their environments or improving their capacity to adapt and respond appropriately to stress-inducing environmental changes [ 30 , 31 ]. Free-range hens may particularly benefit from modifications of their rearing environments, as pullets are reared indoors but adult hens have outdoor access.…”

Impact of Housing Environment on the Immune System in Chickens: A Review

“…One major difference between CC and other housing scenarios is a reduced environmental complexity; CC hens in particular show behavioral, endocrine and immunological signs of stress. In general, environmental enrichment is known to reduce housing stress in birds [26,88,89], and the observation of higher H/L ratios in hens in CC supports this view. Moreover, Campderrich et al [26] demonstrated that laying hens in a complex environment have a better inflammatory response and higher lymphocyte proliferation when exposed to cold stress.…”

“…In general, environmental enrichment is known to reduce housing stress in birds [26,88,89], and the observation of higher H/L ratios in hens in CC supports this view. Moreover, Campderrich et al [26] demonstrated that laying hens in a complex environment have a better inflammatory response and higher lymphocyte proliferation when exposed to cold stress. A recent review by Campbell et al [90], with focus on environmental enrichment during rearing on the behavioral and physiological development of laying hens, also concluded that stress-reducing effects of enrichment are associated with a positive effect on immune competence.…”

“…During their lifespan, chickens are confronted with a wide range of acute and chronic stressors potentially threatening their welfare and health [26]. As in other vertebrate species, stressors activate the hypothalamic-pituitary-adrenal axis and sympathetic-adrenal-medullary axis in birds, resulting in the release of glucocorticoids as well as catecholamines.…”

Environmental Display Can Buffer the Effect of Pesticides on Solitary Bees

“…For mammals, environmental heterogeneity has been found to play a significant role in foraging activities of caged coyotes compared to free range animals [ 10 ]. Chickens placed in more heterogeneous environments with a feeder, wood shavings, and wooden block perches presented a more refined repertoire of behaviours than chickens placed in an area with a feeder and wood shavings only [ 11 ]. Zebra fishes needed additional time to perform activities and were more stressed in simple environments compared to individuals placed in enriched water tanks with the presence of plastic plants, plastic shelter, gravel substrate and a novel object rotated every week [ 12 ].…”