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，每年屠宰超过10亿头猪。生产越来越密集，英国和欧盟的大多数猪都在室内饲养，并在6个月内达到屠宰体重。在这个生产周期中，不熟悉的猪的重新分组是常见的做法，通常在猪的一生中发生几次。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，社会群体之间的迁移是逐渐发生的，等级制度是以最小的侵略性形成的。相比之下，当猪在商业条件下被混入新的群体（重新分组）时，通过激烈的战斗形成了统治等级，许多猪因咬伤而受到100或更多的皮肤抓伤。这对猪来说是压力，导致受伤，增加感染的风险，并减少体重增加。该建议旨在解决猪的重新分组攻击问题。人们对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。这项工作大大受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。在第一类中，被称为自我评估，动物纯粹基于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。当消耗了一定的能量（阈值）后，个体就会放弃，而具有较低阈值的对手将是失败者。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可能会输的战斗。猪是否使用自我或相互评估策略解决战斗对升级的程度有重大影响。通过自我评估，动物总是会战斗到一个阈值，而通过相互评估，使用关于对手的信息将允许较弱的动物迅速放弃它可能会输的战斗。通过研究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。与人类性格相似，猪的攻击性存在个体差异，有些个体比其他个体更具攻击性。这些差异如何影响战斗结果和上述评估类型目前尚不清楚。这将通过一种测量攻击性的技术来揭示。此外，将通过比较经历过重组的猪与先前没有战斗经验的猪来检查战斗经验对发展相互评估能力的重要性。该项目的一个重要方面是旨在优化猪的评估能力，以最大限度地减少重组时的攻击水平。我们将研究是否在生命早期社会化仔猪，通过允许相邻窝断奶前混合，装备猪在以后的生活中的侵略性遭遇相互评估的必要技能。最后，将上述研究成果应用到重组情境中。将操纵小组组成，以优化个人相互评估的能力。这将有助于以最少的战斗形成等级制度。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化生产的猪的福利。

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.