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

Summary
Globally 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.

Technical summary
Aggression between unfamiliar pigs is a major welfare concern. Aggressiveness varies greatly between individuals within many species, the causes of which are poorly understood, limiting our ability to reduce negative welfare impacts. Cognitive ability and affective state are hypothesised to influence information gathering and use during contests, fighting ability (termed resource holding potential; RHP) and contest costs. However, this has never been tested in any species. Here we use pigs as a model system, employing a game theoretical approach to quantify the role of cognitive ability and affective state in contest behaviour. We predict that these factors influence the assessment strategies used during contests. These consist of two broad types: In self assessment models each contestant has knowledge of its own RHP but not that of the opponent. In mutual assessment models individuals compare opponent fighting ability against their own leading to a marked reduction in fight costs. Work suggests that the mutual assessment strategy must be learnt through experience. Here we test: (Obj. 1) if cognition and affect determine success and therefore RHP in a dyadic contest, predicting that cognitively advanced pigs and those with a more positively valenced affective state will win; (Obj. 2) that cognitively advanced pigs make more use of mutual assessment and a positive affective state inflates assessment of own RHP; (Obj. 3) that the affective response to defeat is greater in aggressive pigs and reduces later aggressiveness; and (Obj. 4) that cognitive ability determines contest costs in a commercial group mixing scenario. Obj. 4 is crucial as it predicts that cognitively advanced pigs secure a position in an aggression social network under commercial conditions that minimises fight costs to itself and others but suffers no penalty in dominance. Lastly, we will demonstrate how early life social and physical enrichment can benefit such positive outcomes.

Impact summary

Who will benefit from this research?
Managed animals and animal welfare: Aggression after regrouping of unfamiliar pigs is a major welfare issue and addressing this problem will be of benefit to individual animals.

Pig producers: By engaging with industry, both nationally and internationally, and targeting producers with specific events, research findings will be effectively translated.

Welfare accreditation and regulatory schemes: The findings will help deliver the goals and requirements outlined in welfare accreditation schemes, codes and regulations.

Research staff: The post-doctoral researcher and technicians will gain valuable transferable skills from the project.

Wider public: Consumers are increasingly aware of animal welfare problems associated with the housing and management of animals in intensive agriculture.

How will they benefit from this research?
Managed animals and animal welfare: The work addresses fundamental knowledge gaps in understanding the causes of individual differences in aggressiveness and the negative welfare implications of fighting. Translating new knowledge to reduce fighting could improve the welfare of the vast majority of commercial pigs as regrouping is routine and involves animals at all stages of production. Furthermore, we know almost nothing about how managed animals experience aggression in terms of its effect on their emotional (affective) state. This is a major oversight given that it is one of the most routine challenges to their welfare. Therefore, as well as increasing our understanding of the causes of variation in aggressiveness and how to exploit this to reduce fighting, it will also allow us to assess the affective response to aggression. From this we can better judge the true welfare cost of aggressive behaviour in pigs.

Pig Producers: Regrouping causes injury, poor growth, reduced food conversion efficiency, immunosuppression, a heightened risk of infection and lameness and, in sows, compromised foetal implantation. These are not only welfare concerns but represent a significant economic burden for producers. Reducing regrouping aggression will therefore enhance the economic performance of the industry. This is especially important in an industry with low and variable profit margins that does not receive subsidy support but is regionally important to the rural economy.

Welfare accreditation and regulatory schemes: Farm and abattoir accreditation schemes that certify welfare standards measure outcomes of aggression as a key component (e.g. Red Tractor, RSPCA Freedom Foods, all major retailer codes). The Defra Codes of Practice on Welfare of Pigs and EU Council Directive 2008/120 EC also require actions to be taken to minimise fighting. No auditing scheme, code or directive provides adequate advice on the actions that can best minimise fighting. The impact of such schemes will be strengthened by our findings, providing advice on how the goal of reducing fighting can be achieved in a manner that is commercially applicable.

Research staff: Will gain skills in data collection, analysis and manuscript preparation, as well as developing oral communication skills through presentations to a variety of audiences across the disciplines of applied ethology, animal welfare science and behavioural ecology. Benefits will also flow from working as part of the Easter Bush Research Consortium, one of the largest collections of bioscience researchers globally, and being based within the Roslin Institute Building. Career development will benefit from being exposed to this environment, which provides the ideal opportunity for networking and gaining knowledge. Staff will also have direct contact with industry increasing their experience in the sector.

Wider public: By reduced regrouping aggression, the work will have a positive effect on pig welfare which will be of interest to citizens concerned with animal welfare in intensive agriculture.