Linking the social environment to illness in farm animals

Disease is one of the single largest issues facing food animal agriculture today. Risk factors for various diseases in cattle, swine and chickens include aspects of both the physical and social environment. In this paper we review literature linking the social environment to illness in farm animals, drawing from a conceptual framework developed primarily in the human and laboratory animal literature. To date, researchers have identified various social determinants of disease, have linked social stressors to biological intermediaries and clinical signs of disease, and have established individual behavioural and neuroendocrine differences in susceptibility to disease. Further, ill animals reduce social behaviours as part of a suite of ‘sickness behaviours’. In animal agriculture, the social environment is controlled by management practices implemented on individual farms. Globally, farm sizes are growing, but there is no clear link between farm size and disease incidence. Rather, researchers have tied specific grouping practices, such as moving cows between groups, to increased disease risk, and have begun to determine the biological chain connecting the social world to biological determinants of disease. Studies with farm animals have also established individual variation in behavioural and neuroendocrine response to these practices. Some individuals are more reactive to changes in their social environment than others; however, there remains no consensus on how to recognize these at-risk animals. Additionally, despite the potential role in disease detection, little farm animal work has investigated whether a reduction in social behaviours could be used as early predictors of disease. We end the review by urging further farm animal research to determine the relationship between the social environment and disease, utilizing the concepts and methodologies that have been developed in the human and laboratory animal literature.