Making sense of apparently conflicting data: Stress and immunity in swine and cattle

¹ University of Illinois, Urbana, IL 61801
² Texas Tech University, Lubbock, TX 79409

^* To whom correspondence should be addressed. E-mail: johnso17{at}uiuc.edu.

	Abstract

Stress is generally considered to suppress the immune system and may lead to an increase in disease occurrence in the presence of a pathogen. The immune system is ordinarily brought back to a baseline response level after immune challenge through homeostatic processes in part regulated by the hypothalamic-pituitary-axis. Often, findings reported from various studies investigating the effects of stress on the immune system are conflicting and difficult to reconcile into a cohesive and comprehensible set of universally applicable theories. These discrepancies may be partly explained by the types and durations of the stressors, aspect of immune system measured, genetics, and social status. A particular stressor may enhance cell-mediated immune responses while suppressing humoral responses or vice versa, thus disrupting the balance between these components of the immune system. How farm animals perceive their environment depends not only on traditional environmental stressors (e.g., heat, cold, humidity, pollutants), but also on aspects of their social environment. Dominant animals may have enhanced immune activation while subordinates have suppression of the same immune component in response to the same stressor. This could explain why individual animals within a group respond differently to stressors and disease challenges. A better understanding of the consequences and complex interactions between social and environmental stressors for both innate and adaptive immune traits must be developed so we can more fully understand stress effects on immunity in livestock. Once these complex relationships are better understood, more effective interventions can be designed to improve animal health and well being.

Key Words: Immune system, Stress, T helper Cells, Social status

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