Investigating how the type and quantity of food affect foraging behaviour and the neural circuits controlling feeding in broiler breeder chickens

每年生产的540亿只鸡（肉鸡）占全球肉类消费量的三分之一。鸡肉提供高质量的蛋白质，防止人类营养不良，随着人们变得富裕，全球对肉类的需求不断增长，鸡肉在粮食安全中发挥着重要作用。鸡肉的生产效率也很高，每公斤生产所需的食物投入更少，与其他肉类相比，减少了其碳足迹。由于科学的育种方法，现在肉鸡的生长速度比50年前快了3倍，6周大的雏鸡就能达到2.5公斤的屠宰体重。这一成功是以肉鸡的父母（即肉鸡饲养者）的福利成本为代价的（全球每年估计有3.5亿只鸡）。肉鸡种鸡在20周龄达到性成熟，繁殖到60周龄。因为它们几乎和肉鸡一样有快速生长的潜力，所以必须限制它们的食物来控制它们的生长，否则它们会变得肥胖、不育和不健康，许多会死亡。但是，由于它们的食物配给被限制在它们能吃的三分之一，肉鸡饲养者在几分钟内吃完食物，然后踱步，觅食和啄非食物物体，并将努力工作以获得更多的食物。所有这些都表明，就饥饿而言，他们正在遭受负福利。慷慨饲养和限制饲养都会导致福利问题，这一事实造成了一个被称为“肉鸡饲养者悖论”的伦理困境。一个潜在的解决方案是限制生长，确保身体健康，但通过提供更“饱腹”的食物来减少饥饿。添加膳食纤维会降低食物的能量密度，所以食物的体积越大，摄入的总能量就越少。这种食物需要更长的时间来吃和消化，行为看起来更正常，但它能减少饥饿和提高福利吗？这个项目旨在帮助我们回答这个问题。除了观察不同饮食如何改变行为外，我们还将使用两种新方法来衡量肉鸡饲养员饥饿对福利的影响：1)觅食动机测试，测量鸟类在不提供食物的情况下在新地点觅食（啄和抓）的意愿。因为没有提供食物，所以这个测试在不影响饥饿的情况下测量饥饿。2)测量肠道内的身体系统（神经信号和激素）以及控制饮食行为的大脑部分（下丘脑），我们的重点将放在一种叫做AGRP的物质上。我们已经证明，AGRP可以用来衡量鸡的饥饿程度：AGRP取决于长期（数周）和短期（最近几天）所吃的食物量。根据一项小型实验，我们还怀疑，与通常的定量食物相比，使用高纤维饮食限制生长可能会降低AGRP。我们将把这些衡量标准结合起来，提出以下问题：1)每顿饭和一天中，我们对饥饿的不同衡量标准是如何变化的？2)添加膳食纤维降低能量密度对饥饿感有何影响？3)来自鸡肠道的不同“饱腹”信号是如何被大脑整合的？在最后的部分(4)，我们将应用我们所学到的。我们将测试一家国际家禽养殖公司开发的新型肉鸡种鸡饲粮是否能减少饥饿和提高福利。因此，我们的项目将帮助养鸡业回应社会对动物福利方面的道德关切。最后，由于鸟类和哺乳动物的食物摄入调节在很大程度上是相似的，我们的发现将对那些旨在减少人类肥胖的人感兴趣。特别是，我们对饮食变化的研究，以减少能量摄入，同时促进“饱腹感”和减少饥饿感，与人类减肥的“节食”有关。

The 54 billion chickens produced each year for their meat (broilers) provide a third of global meat consumption. Chicken provides high quality protein, preventing human malnutrition and with the global demand for meat growing as people become richer, chicken meat plays an important role in food security. Chicken is also efficient to produce requiring lower food inputs per kg produced, reducing its carbon footprint compared to other meats.Because of scientific breeding methods, broiler chickens now grow 3 times faster than they did 50 years ago, reaching their 2.5 kg slaughter weight as juveniles at just 6 weeks old. This success has come at a welfare cost to the parents of broilers, known as broiler breeders (estimated 350 million birds per year globally). Broiler breeders reach sexual maturity at 20 weeks and reproduce until 60 weeks of age. Because they have almost the same potential for rapid growth as broilers, they must be food restricted to control their growth, otherwise they become obese, infertile, and unhealthy and many would die. But with their food ration restricted to one-third of what they could eat, broiler breeders finish their food in minutes and then pace, forage and peck at non-food objects, and will work hard to get more food. All of which suggests they are suffering negative welfare in terms of hunger.The fact that both generous and restricted feeding result in welfare problems creates an ethical dilemma known as 'the broiler breeder paradox'. One potential solution is to restrict growth ensuring good health but reduce hunger by providing a more 'filling' food. Adding dietary fibre makes food less energy-dense, so a larger volume of food results in the same total energy intake. This food takes longer to eat and digest, and behaviour appears more normal, but does it reduce hunger and improve welfare? This project aims to help us answer this question.As well as watching how behaviour is changed by different diets, we will use two new approaches to measure the welfare impact of broiler breeder hunger:1) A foraging motivation test which measures how much the bird wants to forage (peck and scratch) in a new location without providing food. Because no food is provided, this test measures hunger without affecting it.2) Measuring the body's systems in the gut (nerve signals and hormones) and in a part of the brain which control eating behaviour (the hypothalamus), where our focus will be on a substance called agouti-related protein (AGRP). We have shown that AGRP can be used as a measure of hunger in chickens: AGRP depends on the amount of food eaten in both the long-term (over several weeks) and the short term (in the last few days). We also suspect, based on a small experiment, that restricting growth using a high fibre diet might reduce AGRP compared to the usual rationed food.We will apply these measures in combination to ask the following questions:1) How do our different measures of hunger vary, meal to meal and over the day?2) How is hunger affected by adding dietary fibre to reduce energy density?3) How are different signals about 'fullness' from the chickens' gut integrated by the brain?In the final part (4) we will apply what we have learnt. We will test whether new broiler breeder diets developed by an international poultry breeding company can reduce hunger and improve welfare. Our project will therefore help the chicken industry to respond to the ethical concerns in society over a difficult aspect of animal welfare.Finally, as food intake regulation is largely similar in birds and mammals, our findings will be of interest to those aiming to reduce obesity in humans. In particular, our investigation of dietary changes to reduce energy intake while promoting 'fullness' and reducing hunger, is relevant to 'dieting' for weight loss in humans.