Stress-Induced Immunomodulation in Low and High Reactive Sheep

SIMPLE SUMMARY: Proper functioning of the immune system is fundamental to maintain animal health; however, several factors can modulate an animal’s immune system, including stress. Farm animals can experience multiple stressors throughout their lifetime, therefore there is a need to know how stress can impact their immune response. Moreover, temperament can affect how an animal responds to a stressor, both behaviorally and physiologically. CarLA is a protective antigen against gastrointestinal nematodes; we wanted to evaluate if there was a relationship between stress and temperament on the CarLA response in ewes. We found that both a 0.5 h and 23 h stressor appeared to have an immunosuppressive effect on CarLA IgA but not total IgA concentrations in ewes and there was some indication that CarLA concentrations were also affected by ewe temperament. More research is needed to understand what these immunosuppressive effects of stress on CarLA IgA concentrations mean in relation to sheep immunity to parasitism using farm relevant stressors. ABSTRACT: The objective of this study was to investigate the relationship between stress and temperament on the humoral immune response of ewes. Eighty ewes were allocated to one of four treatment groups in a 2 × 2 factorial design (n = 20 ewes/treatment): low (LR) and high (HR) reactive ewes were either exposed to no stress (CON) or were visually isolated (STRESS). Ewes remained in treatment pens for 23 h: heart rate was measured continuously, and saliva samples were collected prior to testing and at 0.5 h and 23 h for measurement of cortisol, CarLA IgA and total IgA concentrations. After the first 0.5 h, heart rate was elevated, and cortisol concentrations tended to be higher, whereas CarLa IgA concentrations were lower in STRESS than CON ewes. Similarly, after 23 h, cortisol concentrations remained elevated and CarLA IgA concentrations remained lower in STRESS than CON ewes. Interestingly, total IgA concentrations were not influenced by a 0.5 h or 23 h stressor. Overall, CarLA IgA concentrations were lower in HR than LR ewes at 0.5 h, but there was no significant stress × temperament interaction. Therefore, stress appears to have an immunosuppressive effect on CarLA IgA but not total IgA concentrations in ewes.