Understanding assessment strategies during aggressive encounters in pigs to improve welfare following regrouping.

全球对猪肉的需求正在增加，每年有超过10亿头猪被屠宰。随着英国和欧盟的大多数生猪在室内饲养，并在6个月内达到屠宰体重，生产已经变得越来越集约化。在这个生产周期中，对不熟悉的猪进行重组是一种常见的做法，通常在猪的一生中发生几次。这种不熟悉的猪突然混合在一起，代表了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。这对猪来说是有压力的，导致受伤，增加感染的风险，并减少体重增加。这项提议旨在解决猪的攻击性重组问题。猪用来解决攻击性遭遇的信息收集和决策过程知之甚少。然而，在许多其他动物物种中，有大量关于竞争行为的研究。这项工作得益于基于特定信息收集规则的理论模型的应用。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，使用内部线索，而不参考对手的战斗能力。在战斗上花费了一定(门槛)的能量后，个体将放弃，门槛较低的对手将成为输家。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，因为动物可以很快从一场可能会输掉的战斗中退出。猪是使用自我评估策略还是相互评估策略来解决战斗，对升级的程度有重大影响。有了自我评估，动物总是会战斗到一定的门槛，而通过相互评估，关于对手的信息的使用将允许较弱的动物迅速放弃它可能会输掉的战斗。通过考察两对不熟悉的猪之间的攻击性互动并采用合适的统计框架，该建议将确定所使用的评估策略。与人类个性相似，猪在攻击性方面表现出个体差异，一些个体比另一些个体更具攻击性。这些差异如何影响战斗结果和上文详述的评估类型目前尚不清楚。这一点将通过一种测量攻击性的技术来揭示。此外，将通过将经历过重组的猪与没有战斗经验的个体进行比较，来检验战斗经验对发展相互评估能力的重要性。这个项目的一个重要方面是优化猪的评估能力，以最大限度地减少重组时的攻击性水平。我们将研究在早期生活中通过让相邻的小猪在断奶前进行交配来进行社交是否会使猪具备必要的技能，以便在以后的生活中进行攻击性接触时进行相互评估。最后，将上述研究成果转化为重组情况。小组组成将被操纵，以优化个人相互评估的能力。这将以最少的战斗促进等级制度的形成。实现这一目标并将这一知识转化为工业，有可能改善绝大多数商业生产猪的福利。

Global demand for pig meat is increasing, with over one billion pigs slaughtered annually. Production has become increasingly intensive with most pigs in the UK and EU being raised indoors and reaching slaughter weight within 6 months. During this production cycle, regrouping of unfamiliar pigs is common practice, typically occurring several times during a pig's life. This sudden mixing of unfamiliar pigs represents 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. This is stressful for pigs, resulting in injuries, increased risk of infection, and reduced weight gain. This proposal is aimed at addressing the problem of regrouping aggression in pigs. The information gathering and decision making processes used by pigs to resolve aggressive encounters are poorly understood. However, there is a large body of research on contest behaviour in numerous other animal species. This work has benefitted greatly from the application 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, using internal cues and without reference to the fighting ability of an opponent. After a certain (threshold) amount of energy has been spent on fighting, the individual will give up, and the opponent with the lower threshold will be the loser. 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.Whether pigs settle fights using a self or mutual assessment strategy has major implications for the degree of escalation. With self assessment animals will always fight up to a threshold, whereas with mutual assessment the use of information about the opponent will allow the weaker animal to quickly abandon a fight it is likely to lose. By examining aggressive interactions between pairs of unfamiliar pigs and employing a suitable statistical framework, this proposal will identify the assessment strategy used.Similar to human personalities, pigs show individual differences in aggressiveness, with some individuals being more aggressive than others. How these differences influence fight outcomes and the types of assessment detailed above is currently unknown. This will be revealed using a technique to measure aggressiveness. Additionally, the importance of fight experience for developing mutual assessment ability will be examined by comparing pigs that have experienced regrouping in comparison to individuals with no prior fighting experience. An important aspect of this project is aimed at optimising the assessment abilities of pigs to minimise levels of aggression when regrouped. We will investigate whether socialising piglets during early life, by allowing adjacent litters to mix prior to weaning, equips pigs with the necessary skills for mutual assessment during aggressive encounters later in life. Finally, the above research outcomes will be translated to the regrouping situation. Group composition will be manipulated to optimise the capability of individuals for mutual assessment. This will facilitate hierarchy formation with minimal fighting. Achieving this objective and translating this knowledge to industry has the potential to improve the welfare of the vast majority of commercially produced pigs.