Comparing Physiology, Behaviour and Hippocampal Gene Expression in Laying Hens Housing in Differing Experimental Housing Conditions, and that Exhibited Different Housing Preferences

Design of the housing environment and resources provided may influence the long-term welfare of commercial laying hens. Accessing nest boxes, perches and foraging materials appears to be a behavioural priority for hens, but whether the quality of each alternative is important to their overall experience is unclear. For this reason, hens were housed in an environment that was designed to be “Preferred” (P; n = 15) or “Non-Preferred” (NP; n = 15) for 26 weeks. P pens were large and had deep wood shavings as litter, while NP pens were smaller and had a wire floor. P pens contained more expansive nest boxes and perches than those in the NP pens, along with a peat/sand mix dust bath which was absent from the NP housing. P hens were also given daily positive reinforcers (e.g. food treats), while NP hens experienced negative reinforcers (e.g. water spray). At the end of the housing period, a range of physiological and behavioural measures were taken, and birds were given a series of two-way preference tests between their experimental housing (either P or NP) and a housing environment intermediate to both conditions. Tissue was collected from the HF, and the expression of mRNA transcripts for a range of candidate genes relating to adult hippocampal neurogenesis (AHN) and glucocorticoid regulation was measured using quantitative PCR. Preference for the experimental housing relative to the intermediate conditions was significantly higher for birds housed in P than in NP conditions. However, no other measure differentiated between hens housed in the two conditions. A minority of birds from each condition made the unexpected choice, and serum corticosterone was higher in these individuals than in hens that made the majority choice. In the caudal HF, expression of doublecortin (<i>DCX</i>) mRNA was also lower in hens that made the minority choice. The <i>MR</i>/<i>GR</i> mRNA ratio was lower in the rostral HF of NP housed hens that made the minority choice (in favour of the NP conditions), which might suggest that this subgroup of birds was the most stressed. Expression of proliferative marker <i>PCNA</i> was higher in hens that chose the intermediate conditions over either experimental housing condition. The validity of transcription as a proxy for AHN in chickens is currently uncertain, and consistency between qPCR assays was lower when cDNA came from different reverse transcriptions. However, the existing and novel measures of experience both suggest that variation between individuals, reflected by their preferences, may exceed differences arising from an inanimate housing environment designed to be relatively positive or negative for welfare. Work was approved by the University of Bristol Animal Welfare and Ethical Review Body and conducted under U.K. Home Office Licences (PPL: 30/2779 and 30/3392). Animal use and care was in accordance with the Animals (Scientific Procedures) Act 1986, EU directive 2010/63/EU and the UK Home Office code of practice for the housing and care of animals bred, supplied or used for scientific purposes. Collection and post-mortem analysis of tissue was approved by the Animal Welfare and Ethical Review Body at Newcastle University (Project ID #549). <br>

饲养环境与配套设施的设计，或会影响商品蛋鸡的长期福利水平。蛋鸡往往会优先选择可接触产蛋箱、栖架与觅食材料的环境，但各类设施的品质是否会对其整体生存体验产生影响，目前仍不明确。
基于此，本研究将蛋鸡饲养于两种预设环境中：偏好组（Preferred，P；n=15）与非偏好组（Non-Preferred，NP；n=15），饲养周期为26周。偏好组栏舍空间更大，垫料为厚层刨花；非偏好组栏舍空间更小，地面为金属丝网。偏好组栏舍配备的产蛋箱与栖架规格更大，同时设置了泥炭-沙土混合沙浴池，而非偏好组栏舍未配备该设施。偏好组蛋鸡每日可获得正强化物（如零食），而非偏好组蛋鸡则会接受负强化刺激（如喷水）。
饲养周期结束后，研究人员采集了一系列生理与行为学指标，并让受试蛋鸡开展双向偏好测试：在各自的实验饲养环境（P组或NP组）与介于两种环境之间的过渡饲养环境之间进行选择。研究人员从海马结构（HF）中采集组织样本，采用实时定量聚合酶链式反应（quantitative PCR，qPCR）检测了一系列与成年海马神经发生（adult hippocampal neurogenesis，AHN）及糖皮质激素调控相关的候选基因的mRNA转录表达水平。
相较于过渡环境，偏好组蛋鸡对自身饲养环境的偏好程度显著高于非偏好组。但其余各项指标均未在两组蛋鸡间呈现显著差异。两组中均有少数蛋鸡做出了不符合预期的选择，这类个体的血清皮质酮水平显著高于做出多数选择的蛋鸡。在海马结构后部（caudal HF）中，做出少数选择的蛋鸡的双皮质素（doublecortin，DCX）mRNA表达水平同样更低。非偏好组中做出少数选择（倾向于非偏好环境）的蛋鸡，其海马结构前部（rostral HF）的盐皮质激素受体（MR）/糖皮质激素受体（GR）mRNA比值更低，这或许提示该亚组蛋鸡的应激水平最高。选择过渡饲养环境而非任一实验饲养环境的蛋鸡，其增殖标志物增殖细胞核抗原（PCNA）的表达水平更高。
目前尚不明确mRNA转录水平能否作为鸡类成年海马神经发生的替代指标，且当互补脱氧核糖核酸（cDNA）来自不同逆转录反应时，实时定量PCR（qPCR）检测结果的一致性较差。但无论是现有指标还是新增的体验评估指标均显示，以偏好选择反映出的个体间差异，或许超过了为营造相对正向或负向福利水平而设计的无生命饲养环境所带来的组间差异。
本研究经布里斯托大学动物福利与伦理审查委员会批准，并依据英国内政部许可证（PPL：30/2779与30/3392）开展。动物饲养与实验操作均符合《1986年动物（科学程序）法案》、欧盟2010/63/EU指令，以及英国内政部关于用于科研目的的繁育、供应或使用动物的饲养与护理操作守则。组织样本采集及死后分析经纽卡斯尔大学动物福利与伦理审查委员会批准（项目编号#549）。