The impact of infectious diseases on pig welfare: a scoping review

This scoping review covers the welfare impacts of infectious disease and of interventions used to control infectious disease in pigs. Thirty-three scientific sources were included in the review after literature searches and selection processes, which was a smaller literature than anticipated. We found evidence consistent with infectious diseases causing behavioural and physiological alterations (increased body temperature, anorexia and reduced activity) consistent with a sickness syndrome in pigs. There was also more limited evidence that infectious disease in pigs causes a shift from pro- to negative social behaviours and a reduction in exploration and play. We conclude that this evidence is consistent with infected pigs having reduced welfare. In relation to interventions, studies of the welfare impact of vaccination delivery approaches illustrate the need to evaluate the welfare impacts of disease control methods. Several gaps were identified including a lack of information on the specific welfare impacts of diseases, few papers on the role of environment as a modulator of disease resistance, and an absence of research directly addressing the impacts on pigs' mental state. For interventions there were no reports on the welfare impacts of commonly used disease control methods such as isolation or pharmacological treatment. This review identifies an important opportunity to advance infectious-disease research in pigs by integrating validated and reliable welfare metrics into study methodologies. Doing so will extend the key findings of this review and help address the clear need for more targeted research quantifying welfare impacts across disease conditions.