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

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.

Two major health crises face broiler chicken breeding at the same time as the human population faces a food security crisis. The incidences of leg (varus valgus disease; femoral head necrosis) and heart/lung (pectoral myopathy; cardiac failure; pulmonary hypertension) pathologies increase during broiler ontogeny as activity declines. This incurs huge welfare and economic costs for the billions of broilers raised annually worldwide. Rapid growth rates seem to be a major cause of these problems but no easy solution has emerged. Three related obstacles are critical to any solution: (1) lack of fundamental understanding of how individual organs of the pelvic and pectoral apparatus interact in broilers to produce vital functions such as standing, moving and breathing, (2) how these interactions ultimately influence metabolic cost or stability and (3) how changes in morphology during growth influence those interactions. We propose to resolve these obstacles with an integrative study combining experimental analyses and anatomically-realistic computer simulations of standing, walking and breathing in broiler chickens from 2-6 weeks age, with an emphasis on the three-dimensional linkages between conformation and locomotor and ventilatory mechanics. This would create a new, mechanistically-based approach for quantifying how and why performance in locomotion or breathing differs among broilers of different age, health or conformation, and thus permit scientifically robust, evidence-based industrial and clinical decision-making for broiler breeding. It would thereby supplement and inform existing qualitative tools for evaluating broiler health. This study would build on a wealth of pilot data by the two teams and forge new interactions between them as well as with other researchers and clinicians, the industry and public understanding of this controversial and vital conundrum of poultry biology.

The major non-academic beneficiary of our study would be the poultry industry, exemplified by (but not limited to) our Industrial Project Partner Cobb-Vantress Inc. We already have established links with Cobb (and Aviagen), and the flexibility of our project allows us to build new links with other partners (e.g., Ross), which we shall pursue. Their greatest interest (see Cobb's Letter of Support) will be if we create or inspire/enable the future creation of tools that could directly or indirectly benefit their selection line tools, which would directly influence broiler breeding and thus potentially health. As that is one of our major aims, we expect excellent success in this benefit. Our research in turn would benefit from information from industry on their breeding programmes, extensive databases of morphological measurements and incidences of pathologies, results of different initiatives to improve health or alter growth, and other knowledge that is often confidential unless a formal industrial partnership such as ours with Cobb exists. The public would benefit from an improved understanding of the extremely controversial issue of broiler chicken health and growth, one of the most incendiary topics in animal welfare and food security. We already have experience working on delicate issues such as this from our previous collaborations with the poultry industry as well as on elephant gait and foot pathology in hoofed mammals (JH's past and current BBSRC grants). We see this as an excellent opportunity to engage the public with a study that is not only about a controversial issue of great global interest and importance, but also extremely attractive in terms of its technical aspects- we will generate compelling imagery of the 3D morphology and motions of the broiler musculoskeletal system. In our previous experience the media and public tremendously enjoy such visualizations, which can generate more positive engagement with the scientific process. Our Pathways to Impact outlines approaches (presentations, websites etc) to promote this outcome. In addition to its prominent Animal Health, Animal Welfare, and Economic/Social Impact components emphasised in our proposal, and its international and collaborative scope, this study fits key BBSRC priorities that emphasize its broad strategic relevance to UK, EU and global concerns, such as (also see Pathways to Impact): Ageing and health- the ontogenetic and functional transformations of the broiler musculoskeletal system that our study would focus upon have analogies with changes that occur during ageing in humans. In particular gait pathologies, obesity, and ontogenetic disorders of the musculoskeletal system in humans and other animals have basic principles (e.g. strength:weight ratios; imbalances of organ sizes) in common with problems seen in broiler chickens. Improving broiler health thus should have spin-off benefits to others. Crop/food security- Chicken meat is one of the most popular foods worldwide and is thought to generally be more environmentally friendly and economical than red meat. Food crises are already emerging, so demand for chicken meat is certain to grow, and broiler breeders/farmers are already planning to increase broiler growth rates to fuel this need. The obvious consequences are worsening broiler health crises, so our project is very timely. This issue is also tied to global security; there are growing concerns that the food crisis could (or already has) promote socio-political instability, particularly in these times of economic crisis. Our project also emphasizes the three R's by minimizing invasive research (our locomotor experiments are entirely non-invasive; our ventilatory experiments minimally so), promoting in silico approaches that could eventually help replace such techniques, and using rigorous methodology that will refine future analyses of locomotor and respiratory health. In this way, we lead by example for other researchers.