The translation of animal welfare research into practice: The case of mixing aggression between pigs

•Pig aggression has been an important animal welfare research topic since the 1970s.•The current state of research on aggression in growing pigs and sows is reviewed.•Research has provided various strategies which may partly reduce aggression.•Progress in commercial implementation of effective strategies has been inadequate.•We give recommendations on how to bridge the gap between research and practice. Aggression between unfamiliar pigs at mixing is a major animal welfare problem in commercial farming. It has been studied since the 1970s and remains an important topic in animal welfare research. Methods to reduce pig aggression at mixing have been reviewed previously, but there has been little translation of the advocated techniques and building designs into practice. As a result, the problem persists on many commercial units. A similar situation exists for many other animal welfare issues. This article takes a new approach in not only reviewing the recent scientific literature, but also reviewing the evidence of uptake in industry. Firstly, the current state of aggression mitigation research is reviewed; including the most successful recent developments in breeding against aggression, early life socialisation, the use of pheromones and nutrition. Secondly, information is extracted from both peer reviewed and industry literature to establish the extent to which these strategies have been transferred from research to practice. Finally, we discuss why in spite of the amount of research on reducing aggression at mixing the problem has not reduced in intensive farming systems. The limited uptake in practice appears to be due to low prioritisation of the problem, the practicalities of implementation, lack of information on cost-effectiveness and ineffective communication of research to the farming community. To bridge this gap, industry must be involved in the design of practical solutions and the cost-effectiveness of these must be quantified. This approach should also be considered for other animal welfare issues under investigation. We recommend a better alignment between research questions and industry interests to increase the success of research efforts to improve animal welfare in practice.