|Carroll, Jeffery - Jeff carroll|
Submitted to: Veterinary Clinics of North America
Publication Type: Book / chapter
Publication Acceptance Date: 2/27/2007
Publication Date: 3/22/2007
Citation: Carroll, J.A., Forsberg, N.E. 2007. Influence of stress and nutrition on cattle immunity. In: Olson, K.C., Hollis, L.C., editors. Veterinary Clinics of North America: Food Animal Practice. Amsterdam, The Netherlands: Elsevier Saunders. p. 105-149. Interpretive Summary: Over the last two decades, significant technological advances within the scientific community have occurred allowing further elucidation of the cross-communication which takes place among the endocrine, neuroendocrine, immune, and nutritional processes within the body. Through multi-disciplinary efforts, major advances have been made with regard to linking the effects of stress and nutrition to the immune system. Today, the scientific community readily embraces the fact that stress and nutrition impact every physiological process in the body, and specific mechanisms by which stress and nutrition affect immune function are finally being elucidated. Therefore, the intent of this chapter is to provide an overview of the general concepts of stress and immunology, and to review the effects of stress and nutrition on the immune system of cattle.
Technical Abstract: Scientists have known for decades that "stress" and inadequate nutrition can have detrimental effects on the immune system. However, what had not been distinguished until recently are the divergent effects of "acute" stress compared to long-term or "chronic" stress. As scientists expanded their scope of exploration beyond traditionally defined pathways of neuroendocrinology, endocrinology, and immunology, multidisciplinary efforts emerged that have elucidated cross-communication among these systems and lead to a better understanding of homeostatic regulation within the animal. No longer is the stress response considered an "all or none" biological activity strictly associated with the "fight or flight" behavior, nor is stress considered strictly immunosuppressive. Indeed, stress may elicit "bi-directional" effects on immune function such that acute stress may be immunoenhancing, while chronic stress may be immunosuppressive. While activation of physiological processes in response to an immunological challenge is necessary for survival, there is an associated energy cost to the animal that reduces the overall productivity potential. Indeed, creating and maintaining a febrile response alone is very energy intensive. It has been estimated that there is approximately a 10 to 13% increase in energy usage for every degree of body temperature increase associated with an immune response. Additional energy, above and beyond that necessary for the febrile response, is required for processes such as increased production of inflammatory cytokines, acute phase proteins, and antibody formation. In an effort to compensate for these direct energy requirements, animals will display various behavioral responses such as increased sleep, decreased social activity, decreased sexual behavior and decrease foraging in an effort to conserve energy. Additionally, there are various metabolic changes which occur relative to glucocorticoid and norepinephrine activity which take place in an effort to liberate energy in response to illness. While these behavioral and metabolic responses aid in the animal's effort to conserve energy, they have an overall negative impact on productivity. Utilizing energy resources to mount an adequate immunological response limits the energy that could otherwise be used for other economically important biological functions such as growth, reproduction, and lactation. However, the reality is that activation of the immune system is necessary to prevent disease within the animal, and without diverting nutrients to support immunological functions, there would be significant economic losses associated with death loss, decreased feed efficiency, and reduced average daily gain.