Healthy hen or happy hen? Disease-welfare trade-offs in extensive poultry systems

在消费者对动物福利的关注的推动下，家禽生产系统正在加速从高度集约化（如笼养蛋鸡和大规模室内肉鸡饲养）向更广泛或散养的系统转变。消费者通常没有意识到，强化养殖通过生物安全和打破传播周期为疾病控制带来了重大好处。转向广泛的系统可能会逆转这些好处，导致不同的福利问题，包括疾病和抗菌素使用的增加。虽然原则上有可能优化这种健康-福利权衡，但目前这是不可行的，因为推广与疾病风险之间的联系特征不明确，而且因为优化意味着一种尚不存在的共同货币。以行为自由或“有价值的生活”（包括免于痛苦）为基础的福利指标，与传染病造成的健康状况不佳所造成的广泛承认但缺乏衡量的福利后果存在分歧。必须调和这种不和谐，以设计出同时提供良好健康和良好福利的系统。此外，通过增加抗菌素使用以外的手段在广泛的系统中减少疾病需要创造性的新解决方案，这些解决方案如果成功，可以同时支持健康和福利。假设：-在广泛的家禽系统中，鸟类感染环境传播寄生虫的程度较高；-这些寄生虫与健康状况不佳和生产结果有关；-保健和其他福利指标可以合并为一种有意义的单一货币，以便在各个方面进行优化；-对粗放系统的修改可以在不损害其他福利的情况下改善健康状况，最大化推广的效益。工作计划-对集约化-粗放化梯度下的蛋鸡和肉鸡养殖户进行寄生虫感染和寄主状况样本研究，涵盖集约化、商业粗放化和具有各种住房系统的小农鸡群。通过问卷调查和半结构化访谈收集住房制度、抗菌药物（包括抗球虫和驱虫药）使用和健康问题的详细信息。该学生将访问沿着集约化-粗放化梯度选择的农场子集，采集粪便样本，并在正常农场管理（屠宰或扑杀）下采集尸体样本，以便在死后评估寄生虫和病原体负担。下一代测序将用于测量粪便中的病原体多样性。包括生长率、产蛋量和质量在内的性能指标将在鸡群和可能的情况下在单个鸟的水平上收集；有福利基准指标。将使用广义线性混合模型分析数据，以表征住房系统与寄生虫和病原体的负荷和多样性之间的相关性，以解决第一个假设。-开发和应用精确干预措施，以降低大范围环境中的感染风险。将为发现的主要宏观和微寄生虫物种（包括蛔虫、球虫和关键细菌物种）开发种群动态模型，使用已建立的SIR数学框架，但使用Netlogo软件，明确考虑住房空间（室内和室外），从而通过空间聚类增加宿主密度和接触率的变化。这些模型将用于评估住房改进对寄生虫传播的影响。选定的干预措施将在大量出现疾病问题的禽群中进行试验，并衡量对感染、性能和福利的影响。-结合福利指标并评估系统变化和干预措施的后果将在生产系统和访谈（生产者，健康顾问和公众）中比较个人福利指标，以获得新的疾病福利指标。

Change in poultry production systems from highly intensive eg caged laying hens and mass indoor broiler rearing, towards more extensive or free-range systems is accelerating, driven by consumer concerns over animal welfare. Consumers are generally unaware that intensification brought significant benefits for disease control through biosecurity and breaking transmission cycles. Moving to extensive systems risks reversing those benefits, leading to different welfare problems including from disease and increased antimicrobial use. While possible in principle to optimize such health-welfare trade-offs, this is not currently feasible because the link between extensification and disease risk is poorly characterized, and because optimization implies a common currency that does not yet exist. Welfare indicators based on behavioral freedoms or a 'life worth living', including freedom from pain, have diverged from the widely acknowledged but poorly measured welfare consequences of poor health due to infectious diseases. This dissonance must be reconciled to design systems that deliver good health and good welfare together. Moreover, the abatement of disease in extensive systems by means other than increased antimicrobial use requires creative new solutions, which if successful could simultaneously support health and welfare. Hypothesis:-Birds in extensive poultry systems experience higher levels of infection with environmentally transmitted parasites;-These parasites are associated with poor health and production outcomes;-Health and other welfare indicators can be combined into a meaningful single currency for optimization across dimensions;-Modification of extensive systems can achieve improved health without compromising on other welfare, maximizing benefits of extensification.Work plan-Sample parasite infections and host status across intensive-extensive gradientLaying hen and broiler farmers will be recruited spanning intensive, commercial extensive and smallholder flocks with a variety of housing systems. Details of housing system, antimicrobial (including anticoccidial and anthelmintic) usage and health problems will be collected by questionnaire and semi-structured interview. The student will visit a subset of farms chosen along an intensive-extensive gradient to sample faeces and, where available under normal farm management (slaughter or culling), carcases for post mortem assessment of parasite and pathogen burdens. Next generation sequencing will be used to measure pathogen diversity from faeces. Performance metrics including growth rates and egg yield and quality will be collected at flock and, where possible, individual bird levels; with welfare benchmark indicators. Data will be analysed using generalized linear mixed models, to characterize correlations between housing system and the load and diversity of parasites and pathogens, to address the first hypotheses.-Develop and apply precision interventions to attenuate infection risk in extensive settingsPopulation dynamic models will be developed for the major macro and microparasite species found, to include ascarid worms, coccidia and key bacterial species, using established SIR mathematical frameworks but using Netlogo software to add explicit consideration of housing space (indoor and outdoor) and hence variation in host density and contact rates through spatial clustering. The models will be used to evaluate the impact of refinements to housing on parasite transmission. Selected interventions will be trialed in participating extensive flocks experiencing disease problems and impact on infection, performance and welfare measured.-Combine welfare metrics and evaluate consequences of system change and interventionsIndividual welfare indicators will be compared across production systems and interviews (of producers, health advisors and the public) on perceptions of welfare and disease impacts used to derive a novel disease welfare indicator.