Demand-driven solutions to reduce aggression between pigs

Abstract

Aggression between pigs is common in commercial farming as pigs fight to establish dominance relationships at regrouping. The behaviour has been studied extensively since the 1970s and several strategies to reduce aggression have been identified. However, the uptake of aggression research in commercial practice has been limited and the behaviour remains an important problem for animal welfare, farm productivity and profitability. This thesis is the first body of work to study the social and economic factors influencing farmers’ behaviour regarding the management of aggression, and adopted quantitative research methods in order to meet two primary aims. The first aim was to understand the behaviour of UK and Irish pig farmers with regard to aggression between pigs. This was important because understanding behaviour and the context in which is occurs can help to identify targets for initiating a change in practice. The second aim was to identify practical and cost effective solutions based on farmer demand. This is important because solutions based on industry input have the capacity to make real improvements to animal welfare in practice. At various stages of this project farmers perceptions of pig aggression and welfare were compared to other stakeholder groups in order to establish the impact of farmers’ role and experience. Comparison groups had experience of working with pigs but in a different context (specialised pig veterinarians); had knowledge of agriculture and livestock but no experience of working with pigs (agriculture students and animal science students); and were removed from animal production (citizens unrelated to agriculture).

The first aim of this thesis was addressed in the first three studies. The results of the first study revealed widespread belief in pigs’ capacity to suffer amongst pig farmers (and non-farmers). Therefore, a lack of belief in pigs’ capacity to suffer does not appear to contribute to the non-financial reasons behind farmers’ reluctance to control pig aggression. In the second study, participants perceptions of aggression seen in video clips were compared to physiological measures of exhaustion (blood lactate) and injury (lesion score) taken from the animals. Results revealed that farmers’ (and non-farmers) recognised fights displayed in-action as a source of suffering for pigs. However, when they did not see the fight occurring but only saw the animals afterwards, participants underestimated pigs’ injuries. In the third study, an in-depth analysis of the range of factors likely to influence farmer behaviour revealed that farmers’ willingness to control aggression was influenced by: 1) whether they felt able to implement the change, 2) beliefs about the likely consequences, 3) perceptions of aggression as a problem on their farm, and 4) the opinion of relevant stakeholder groups, with the opinion of veterinarians being particularly significant.

The second aim of this thesis was addressed in the final two studies. In the fourth study, an economic choice experiment revealed three independent groups of pig farmers, each with different willingness to pay (WTP) for aggression control strategies and motivation for making an investment. Specifically, farmers in Class 1 would not invest in an aggression control strategy as they were unlikely to regroup unfamiliar pigs. Farmers in Class 2 were willing to invest in an aggression control strategy, but were only interested in the extent to which the strategy improved growth rate. They were unwilling to pay for reductions in aggression specifically. Farmers in Class 3 were motivated by reducing aggression as well as improving growth rate, and were WTP £0.11 per pig place and £0.03 per pig produced for each 1% reduction in lesions as result of aggression. In the final study, cost-benefit analysis revealed that allowing litters to co-mingle prior to weaning is the most practical and economically viable aggression control strategy; meeting the demands of farmers in both Classes 2 and 3. Exposing pigs to synthetic maternal pheromones was unlikely to improve profitability, but did meet the WTP demands of farmers in Class 3. Changing current structures in order to house pigs in large social groups (100+ pigs) was associated with high economic costs which were not within the realms of farmers’ WTP. Overall, a major barrier preventing the uptake of aggression research in practice is that very few strategies can be practically and cost-effectively implemented and managed by farmers under commercial conditions.

Based on the findings of this project, several evidence-based recommendations were made to encourage a real change in practice. For example, animal scientists working on the control of aggression should test new strategies for their practicality and cost-effectiveness. Furthermore, communication within the industry must take place through targeted campaigns which take care to consider the wide variety of factors which influence farmers’ behaviour. Applying the social sciences to stubborn and entrenched animal welfare issues has the capacity to bridge the gap between animal science research and practice, and have a huge impact on farm animal welfare. Therefore, the approach adopted in this project should be extended to other long-standing animal welfare issues where known solutions are poorly adopted.