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。生产变得越来越集约化，英国和欧盟的大多数猪都在室内饲养，在6个月内达到屠宰体重。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，通常在猪的一生中会发生几次。这种不熟悉的猪的突然混合代表了一个主要的动物福利问题。家猪的社会结构是建立在统治等级的基础上的。在野外，社会群体之间的迁徙是逐渐发生的，等级制度是在最小的攻击下形成的。相比之下，当猪在商业条件下被混合到新的群体（重组）时，统治等级是通过激烈的战斗形成的，许多猪被咬伤100或更多的皮肤。这给猪带来了压力，导致受伤，感染风险增加，体重增加减少。本提案旨在解决猪的重组攻击问题。人们对猪在应对攻击性遭遇时所使用的信息收集和决策过程了解甚少。然而，对许多其他动物物种的竞争行为进行了大量研究。这项工作很大程度上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。第一种是自我评估，动物完全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。在战斗中消耗了一定（阈值）的能量后，个体将放弃，而阈值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，但也使用有关对手战斗力的信息。虽然更复杂，但它有更大的好处，因为动物可以迅速退出它可能输掉的战斗。猪是使用自我评估策略还是相互评估策略来解决争端，对冲突升级的程度有重要影响。有了自我评估，动物总是会战斗到一个阈值，而有了相互评估，利用对手的信息，较弱的动物就会迅速放弃可能输掉的战斗。通过检查不熟悉的猪对之间的攻击性相互作用，并采用合适的统计框架，本提案将确定所使用的评估策略。与人类的性格相似，猪在攻击性方面也表现出个体差异，有些个体比其他个体更具攻击性。目前尚不清楚这些差异如何影响战斗结果和上述详细的评估类型。这将通过一种测量攻击性的技术来揭示。此外，战斗经验对发展相互评估能力的重要性将通过将经历过重组的猪与没有先前战斗经验的猪进行比较来检验。该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水平。我们将研究在断奶前允许相邻的窝混合在一起，从而使仔猪在早期生活中进行社交，是否能使猪在以后的生活中具有相互评估的必要技能。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结构的形成。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养殖猪的福利。

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.