Determining how cognitive ability and affective state impact assessment strategies during aggressive contests to improve pig welfare after regrouping

摘要全球每年屠宰10亿头猪，英国和欧盟的大多数猪都是在密集的室内系统中饲养的。重组不熟悉的猪是一种常见的做法，在猪的一生中会发生几次。这种不熟悉的猪突然混合在一起是一个主要的动物福利问题。家猪的社会结构是以优势等级为基础的。在野外，社会群体之间的迁徙是逐渐发生的，等级制度的形成具有最小的攻击性。相比之下，当猪在商业条件下被混入新的群体(重新组合)时，通过激烈的战斗形成优势等级，许多猪因咬伤而受到100或更多的皮肤抓伤。感染的风险增加，体重增加也会减少。这项建议旨在解决猪的攻击性重组问题，但预计它将有助于理解广泛物种的攻击性。猪个体之间的攻击性存在很大差异。目前，我们对这种变化的原因知之甚少，因此无法防止表现出极端的攻击性。攻击性的比赛要求动物做出快速和知情的决定，这要求它们吸收和处理复杂的信息，并将其转化为知识(一种称为认知能力的技能)。动物在遭遇攻击性之前的情绪也可能决定它的攻击性行为，而对一场比赛的输赢的情绪反应可能会影响它随后的攻击性。然而，尽管认知能力和情绪状态可能在很大程度上导致了个体在攻击性行为和受到的伤害方面的差异，但这一点从未在任何物种中进行过测试。在这里，我们量化了这些因素在比赛中表现出的行为中的重要性。在行为生态学领域，对竞赛行为的理解大大得益于基于特定信息收集规则的理论模型的使用。已经开发了两类模型，它们在比赛中使用的策略不同。在被称为自我评估的第一类课程中，动物纯粹根据自己的战斗能力和耐力做出战斗决定，而不参考对手的战斗能力。在战斗中花费了一定的能量后，个人就会放弃。在第二类模型中，称为相互评估，动物自我评估，但也使用关于对手战斗能力的信息。虽然更复杂，但它有更大的好处，因为动物可以迅速退出一场可能会输掉的战斗，并大幅减少受伤人数。这个项目测试了这样的假设：(I)认知先进的猪赢得了相遇，并更多地利用了相互评估，减少了打斗造成的伤害；(Ii)打架前积极的情绪状态会让动物对自己的打斗能力有更大的看法，并缓冲失败的效果；以及(Iii)输掉一场打斗对攻击性猪的情绪状态的负面影响比攻击性较弱的猪更负面，这种情绪反应会影响后来的攻击性。最后，我们将以商业现实的方式对猪进行重组(12只动物一组)，以测试认知能力是否决定了现实世界中的比赛成本。在这里，我们期待一头认知先进的猪能够将自己和他人的战斗成本降至最低，同时在统治地位上不受惩罚。在整个过程中，该项目将通过改变动物在早期生活中获得的社交和身体丰富的数量来最大化认知能力和情绪状态的差异。因此，我们将测试由于提高认知能力和情绪状态而导致的攻击性成本的降低是否可以通过管理变革来刺激。如果是这样的话，将这些信息转化为行业可能会让大多数商业化生产的猪受益。

SummaryGlobally one billion pigs are slaughtered annually and most pigs in the UK and EU are raised in intensive indoor systems. Regrouping of unfamiliar pigs is common practice and occurs several times during a pig's life. This sudden mixing of unfamiliar pigs is a major animal welfare concern. The social structure of domestic pigs is based on a dominance hierarchy. In the wild, migration between social groups occurs gradually, and hierarchies are formed with minimal aggression. In contrast, when pigs are mixed into new groups (regrouped) under commercial conditions, dominance hierarchies are formed through vigorous fighting, with many pigs receiving 100 or more skin scratches caused by biting. Increased risk of infection, and reduced weight gain also occur. This proposal aims to address the problem of regrouping aggression in pigs but it is expected to be of benefit in understanding aggressiveness in a wide range of species.Great variation exists in aggressiveness between individual pigs. At present we know little about the causes of this variation and therefore cannot prevent the expression of extreme aggression. Aggressive contests demand that animals make rapid and well-informed decisions, which requires that they assimilate and process complex information and turn it into knowledge (a skill termed cognitive ability). The mood of an animal before an aggressive encounter also likely determines its aggressive behaviour and the emotional response to winning or losing an encounter likely affect its subsequent aggressiveness. However, although cognitive ability and emotional state probably contribute substantially to differences between individuals in their aggressive behaviour and the injuries they receive, this has never been tested in any species. Here we quantify the importance of these factors in the behaviour shown during contests. In the field of behavioural ecology, understanding of contest behaviour has benefitted greatly from the use of theoretical models that are based on particular information gathering rules. Two classes of model have been developed that differ in the strategies used during contests. In the first class, termed self assessment, animals make fight decisions based purely on their own fighting ability and stamina, without reference to the fighting ability of an opponent. After a threshold amount of energy has been spent on fighting, the individual will give up. In the second class of model, termed mutual assessment, animals self assess but also use information about the fighting ability of an opponent. Although more complex, it has greater benefits as an animal can quickly withdraw from a fight it is likely to lose and substantially reduce the amount of injuries. This project tests the hypotheses that (i) cognitively advanced pigs win encounters and make greater use of mutual assessment with reduced injuries from fights; (ii) that a positive emotional state before a fight inflates the animal's view of its own fighting ability and buffers the effect of defeat; and (iii) that losing a fight has a more negative effect on the emotional state of an aggressive pig than a less aggressive one and this emotional response influences later aggressiveness. Finally, we will regroup pigs in a commercially-realistic way (groups of 12 animals) to test whether cognitive ability determines contest costs in the real world. Here we expect that a cognitively advanced pig is able to minimise fight costs to itself and others whilst suffering no penalty in dominance. Throughout, the project will maximise variation in cognitive ability and emotional state by varying the amount of early-life social and physical enrichment the animals receive. We will therefore test whether reductions in the costs of aggression as a result of enhancing cognitive ability and emotional state can be stimulated by management changes. If so, translating these messages to industry could benefit the majority of commercially produced pigs.