ISSUE FOCUS FEED & ADDITIVE MAGAZINE June 2022 35 The adaptive processes can further include physiological, neuro-endocrine and cellular responses. Some of the physiological parameters for adaptation to rising temperatures are respiration rate, pulse rate, skin temperature and sweating. However, there are differences between species in the expression of these characteristics. For example, poultry has the characteristics of rich feathers, no sweat glands, strong metabolism and high body temperature. As a result, the production performance of poultry is easily impacted by elevated ambient temperatures. Research into the physiological changes accompanying high temperatures in tropically adapted species is increasing the understanding of the mechanisms that the animal uses to accomplish the necessary functions effectively, and to find ways to support a more efficient response to minimize the negative impact on performance and animal wellbeing. Identifying relevant biomarkers in animals capable of maintaining high levels of productivity at high ambient temperatures will also help to breed for climate resilient animals. ADAPTIVE RESPONSES AT THE CELLULAR LEVEL Exposure to challenges, including environmental ones such as ambient temperatures above thermal comfort zones, induce adaptive responses that allow cells and organisms to continue normal functions in the face of adverse stimuli. At the cellular level adaptive responses involve multiple changes in gene and protein expression, including induction of cellular defenses, e.g., antioxidants and heat shock proteins to enable the cell to survive. On the other hand, exposure to challenges will increase cellular levels of reactive oxygen species (ROS). The balance between the generation of ROS and cellular antioxidants determines the level of oxidative stress, which again impacts the animal’s ability to attain performance potential and sustain good health. A key cellular adaptation mechanism discovered in species surviving extreme environmental conditions is the enhanced expression of the cytoprotective system NRF2-KEAP1, which is involved in protection from oxidative stress, detoxifaction and protein homoeostasis. The nuclear factor erythroid 2–related factor 2 (NRF2), is part of a complex regulatory network that responds to environmental cues. The subsequent evolution of cysteine-rich Kelch-like ECH-associated protein 1 (KEAP1) provided animals with a more sophisticated way to regulate NRF2 activity. Exposure to oxidants disrupts the interaction between NRF2 and KEAP1,
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