Towards the chicken of the future: biomechanical compromises and constraints on locomotion and breathing in broiler chickens

每年有超过300亿只肉鸡被饲养供人类食用;英国有8亿只。在这些动物中，近30%的动物会出现某种形式的明显跛行以及心肺问题，仅在英国每年就花费约2000万英镑。这些问题与快速生长率的选择性育种有关-肉鸡只需要6周就可以达到近3公斤的屠宰质量，而20世纪50年代需要15周。因此，肉鸡的骨骼和其他系统是不成熟的，随着它们长大，适应环境的能力受到损害。随着肉鸡年龄的增长，活动水平急剧下降。与不活动有关的福利问题随着年龄的增长而增加，有争议但越来越多的证据表明屠宰年龄的肉鸡处于痛苦之中。然而，全球粮食安全取决于经济和环境友好的鸡肉。我们建议开发一个新的科学框架，以了解肉鸡的身体如何随着生长而变化，重点关注站立和行走过程中腿部及其肌肉的功能，以及站立，坐下和行走时呼吸过程中胸部肌肉的功能。这个框架将建立在一个非常严格的三维分析（使用X射线）的骨骼实际上是如何移动的肌肉在运动和呼吸。它将用于步态（包括稳定性）和呼吸（包括不同活动的代谢能量成本）实验分析的尖端技术与肌肉骨骼系统如何产生观察到的运动的解剖学逼真的3D计算机模拟相结合。我们对这些方法的新颖综合将使我们能够梳理出肉鸡的体形和姿势在生长过程中如何变化，以及这些变化如何影响站立，移动和呼吸。它将揭示生长、健康和行为之间的权衡，填补我们对肉鸡生物学理解的一个重大空白--研究尚未深入活体肉鸡内部，看看它们的成分如何发挥作用以实现观察到的行为，以及这些成分的相互作用如何影响肉鸡的生活。相反，大多数研究都集中在生活中对“跛行”和“腿无力”的外部定性观察或对许多特定疾病的死后诊断。本研究旨在通过跨越肉鸡功能器官、生物体和种群之间的差距来纠正这种不平衡。我们怀疑，在2周龄时，肉鸡的运动和呼吸能力相当熟练，但这些能力往往在4周龄时下降，并在6周龄时接近可行性能的极限。这些下降可能是由于可食用的胸部肌肉的快速增长，使身体“前部沉重”，使动物不稳定，导致腿部更难支撑，同时引起呼吸困难。这种恶性循环会导致疲劳、不活动和健康状况不佳，这与人类肥胖危机相似，但没有简单的解决方案。了解选择性育种对肉鸡的详细解剖结构所做的工作以及这如何影响其功能能力，对于解决肉鸡腿部和肺部健康这两个相关危机至关重要。此外，在鸡生长的早期，可能有一个最佳的身体结构（如更大的腿，不同的胸肌分布）。如果科学地确定了这一最佳值，就可以通过选择性育种来减少这些问题--正如我们所希望的那样。我们的研究将提供一个新的理解解剖，生长，站立和移动，呼吸和代谢能量成本之间的联系在肉鸡，这将使我们能够建立一个新的方式来评估哪些鸡移动和呼吸最好，为什么。这将有助于科学家，临床医生和行业共同努力，促进更好的肉鸡健康和福利，同时仍然养活世界。

Each year over 30 billion broiler chickens are bred for human consumption; 800 million in the UK. Of these animals, almost 30% develop some form of obvious lameness as well as heart and lung problems, costing around £20million/year in the UK alone. These problems are linked to selective breeding for rapid growth rates- broilers take only 6 weeks to reach a slaughter mass of almost 3kg, which has changed from 15 weeks in the 1950s. As a result, the skeletons and other systems of broilers are immature, with compromised abilities to adapt to their environment as they grow to large sizes. Activity levels decline steeply as broilers age. Welfare problems related to inactivity increase with age and there is controversial but building evidence that slaughter-age broilers are in pain. However global food security depends on economical and environmentally-friendly chicken meat. We propose to develop a new scientific framework for understanding how the bodies of broilers change as they grow, focusing on the functions of the legs and their muscles during standing and walking, and the functions of the chest muscles during breathing when standing, sitting and walking. This framework would be founded on an extremely rigorous three-dimensional analysis (using x-rays) of how the skeleton actually is moved by the muscles during locomotion and breathing. It combines cutting-edge techniques for the experimental analysis of gait (including stability) and breathing (including metabolic energy cost for different activities) with anatomically-realistic 3D computer simulations of how the musculoskeletal system produces observed motions. Our novel synthesis of these approaches will allow us to tease apart how the body shape and posture of broilers changes as they grow and how these changes influence standing, moving and breathing. It will reveal tradeoffs between growth, health and behaviour, by filling a major gap in our understanding of broiler biology- studies are yet to peer inside living broilers to see how their components work to achieve observed behaviours and how the interactions of these components influence the lives of broilers. Instead, most research has focused on external, qualitative observations of 'lameness' and 'leg weakness' during life or post-mortem diagnoses of numerous specific disorders. This study aims to redress this imbalance by spanning the gap between functioning organs, organisms and populations of broilers. We suspect that at 2 weeks of age broilers are quite adept at locomotion and breathing but these abilities tend to decline at 4 weeks and approach limits of viable performance at 6 weeks old. These declines could be driven by the rapid growth of edible breast muscles that make the body 'front heavy,' destabilizing the animal and causing the legs work harder for support, and concurrently incurring breathing difficulties. This vicious cycle would lead to fatigue, inactivity and poor health that has parallels with the human obesity crisis, but there is no simple solution to it. Understanding what selective breeding has done to the detailed anatomy of broilers and how this has affected their functional abilities is pivotal to any solution to the two related crises of leg and lung health in broilers. Furthermore, there may be an optimal body structure (such as larger legs, different breast muscle distribution) at some point early in chicken growth. This optimum could be promoted by selective breeding to reduce these problems if it were determined scientifically- as we intend. Our study would provide a new understanding of the linkages between anatomy, growth, standing and moving, breathing and metabolic energy costs in broiler chickens that would enable us to forge a new way of assessing which chickens move and breathe the best and why. This would help scientists, clinicians and industry to work together to promote better broiler health and welfare while still feeding the world.