BILL E. KUNKLE INTERDISCIPLINARY BEEF SYMPOSIUM: Overlapping physiological responses and endocrine biomarkers that are indicative of stress responsiveness and immune function in beef cattle

摘要

Acknowledgment that modern livestock production systems impose stress on animals has been accepted by the scientific community and producers. As the economic burden has increased for livestock producers, expectations for animal performance have increased, thus placing more strain on the entire production system. Whether or not periodic exposure to stress within the production system jeopardizes the well-being of animals continues to be an area of debate largely because of the inability to accurately quantify the magnitude and severity of the stress response on other biological systems. Adding to the confusion is the fact that activation of the stress axis can be both beneficial and detrimental to the body depending on the duration of the stress response and the frequency at which an animal is exposed to stressful stimuli. Few would argue that continuous long-term stress inhibits livestock productivity and overall wellbeing. Less clear is whether or not occasional exposure to acute stress jeopardizes the productivity and well-being of livestock. To fully appreciate the complexity associated with activation of the stress axis and the overall biological impact on the body, one must delve deep into the scientific literature and examine the science in an unbiased manner. It is imperative to appreciate and understand that activation of the stress axis is an essential survival mechanism necessary to maintain homeostasis during biologically challenging times. Acute activation of the stress axis leads to repartitioning of energy to organs and tissues essential for coping with stress, redirection of blood flow from the peripheral to large muscle groups, decreased digestive function, and priming of the immune system to prepare for subsequent infections. Conversely, chronic activation of the stress axis disrupts digestive function, causes catabolism of muscle and adipose tissue, and suppresses overall immune function, thus making an animal more susceptible to disease. But what parameters are needed to distinguish periods of acute stress from those of chronic stress, and what biological markers are the best indicators of "stress" in an animal? Although there are a plethora of physiological responses and endocrine biomarkers that can be quantified, an integrative tool that has been readily embraced by scientists and producers as an effective and efficient indicator of the duration and magnitude of stress that an animal is experiencing has yet to be identified.