Nordgreen Janicke, Dumontier Lucille, Smulders Tom V, Vas Judit, Palme Rupert, Janczak Andrew M
Department of Paraclinical Sciences, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, 1433 Ås, Norway.
Centre National de la Recherche Scientifique, Institut Français du Cheval et de L'équitation, Institut National de Recherche Pour L'agriculture, L'alimentation et L'environnement, Unite Mixte de Recherche Physiologie de la Reproduction et des Comportements, Universitè de Tours, 37380 Nouzilly, France.
Animals (Basel). 2024 Nov 26;14(23):3422. doi: 10.3390/ani14233422.
The hypothalamic-pituitary-adrenal (HPA) axis responsivity is influenced by early life experience and also modified by the environment an individual experiences as an adult. Because laying hens are transferred from rearing to laying farms at 16-18 weeks of age, they are well suited to study the interaction effect between early (rearing) and adult (laying) environments on physiology and behaviour. In the European Union, there is a move towards cage-free systems for laying hens, but globally, the majority of layers are kept in conventional or furnished cages. Conventional cages have no enrichment, whereas furnished cages have little enrichment. Both cage types limit the movement of birds and the expression of highly motivated behaviours. Lack of enrichment may lead to under-stimulated birds that are more sensitive to stress and fear-inducing challenges later in life. Fearfulness has been linked to feather pecking, which has negative consequences for animal welfare and productivity. Previous research has shown that birds reared in cages are more fearful and perform more poorly in a test of spatial cognition than birds reared in aviaries when tested within five weeks after transition to adult housing. However, recent results suggest that these effects might not be long-lasting. We, therefore, tested the effect of the early (rearing) (aviary vs. cage) and adult (laying) environments (standard vs. additionally enriched furnished cages) on the corticosterone response to restraint in birds that were 35 weeks into lay (i.e., 52 weeks of age) and assessed their plumage condition. We hypothesised that a lower level of enrichment, both during rearing and adulthood, would represent a lower level of stimulation, resulting in a stronger corticosterone response to restraint and poorer feather cover. Both stressed (restrained) and control birds increased their corticosterone levels from the first (baseline) to second sample ( < 0.01 for both), but the increase in the restrained group was significantly higher than in the control group (F = 9.51; = 0.003). There was no effect of the early environment, but birds housed in standard furnished cages as adults had overall higher corticosterone levels than birds housed in enriched furnished cages regardless of their early life environment (F = 4.12; = 0.048). Neither early nor adult housing influenced the feather score except for on the belly, where birds housed in enriched cages as adults had a poorer feather score, contrary to our prediction. In conclusion, no effect of the early environment on HPA axis responsivity to an acute stressor could be detected at 52 weeks of age, but adult enrichment had a favourable effect on overall corticosterone levels.
下丘脑 - 垂体 - 肾上腺（HPA）轴反应性受早期生活经历影响，也会因个体成年后所经历的环境而改变。由于蛋鸡在16 - 18周龄时从育雏场转移至产蛋场，它们非常适合用于研究早期（育雏）和成年（产蛋）环境对生理和行为的交互作用。在欧盟，正朝着蛋鸡的非笼养系统发展，但在全球范围内，大多数蛋鸡仍饲养在传统或有设施的笼子里。传统笼子没有富集物，而有设施的笼子只有少量富集物。两种笼子类型都限制了鸡的活动以及高动机行为的表达。缺乏富集物可能导致鸡受到的刺激不足，使其在日后生活中对压力和引发恐惧的挑战更加敏感。恐惧与啄羽行为有关，这对动物福利和生产力有负面影响。先前的研究表明，与在成年鸡舍饲养5周内接受测试时饲养在鸟舍中的鸡相比，饲养在笼子里的鸡更易恐惧，并且在空间认知测试中的表现更差。然而，最近的结果表明这些影响可能不会持久。因此，我们测试了早期（育雏）环境（鸟舍与笼子）和成年（产蛋）环境（标准与额外富集的有设施笼子）对35周龄产蛋期（即52周龄）鸡在受到束缚时皮质酮反应的影响，并评估了它们的羽毛状况。我们假设，在育雏期和成年期富集程度较低代表刺激水平较低，会导致对束缚的皮质酮反应更强且羽毛覆盖状况更差。应激（受束缚）组和对照组的鸡从第一个（基线）样本到第二个样本时皮质酮水平均升高（两组均P < 0.01），但受束缚组的升高幅度显著高于对照组（F = 9.
