A 100-Year Review: Stress physiology including heat stress

Abstract

Stress is an external event or condition that places a strain on a biological system. The animal response to a stress involves the expenditure of energy to remove or reduce the impact of the stress. This increases maintenance requirements of the animal and results in loss of production. The biological response to stress is divided into acute and chronic phases, with the acute phase lasting hours to a few days and the chronic phase lasting several days to weeks. The acute response is driven by homeostatic regulators of the nervous and endocrine systems and the chronic phase by homeorhetic regulators of the endocrine system. Both responses involve alterations in energy balance and metabolism. Thermal environment affects all animals and therefore represents the largest single stressor in animal production. Other types of stressors include housing conditions, overcrowding, social rank, disease, and toxic compounds. "Acclimation" to a stress is a phenotypic response developed by the animal to an individual stressor within the environment. However, under natural conditions, it is rare for only one environmental variable to change over time. "Acclimatization" is the process by which an animal adapts to several stressors within its natural environment. Acclimation is a homeorhetic process that takes several weeks to occur and occurs via homeorhetic, not homeostatic, mechanisms. It is a phenotypic change that disappears when the stress is removed. When the stress is severe and not relieved by acclimatization or management changes, the animal is considered chronically stressed and is susceptible to increased incidence of disease and poor health. Milk yield and reproduction are extremely sensitive to stress because of the high energy and protein demands of lactation and the complexity of the reproductive process and multiple organs that are involved. Improvements in protection of animals against stress require improved education of producers to recognize stress and methods for estimating degree of stress on animals.

Size does matter: Parallel evolution of adaptive thermal tolerance and body size facilitates adaptation to climate change in domestic cattle

“…The RE of ATP1A1, GAPDH, and ACTB genes showed similar trends in both dwarf and standard size breeds low hemoglobin level in SCB reflects low protection against oxidative damage, making them more vulnerable to stress (Collier et al, 2017). Likewise, a significantly higher respiratory rate in SCB than DCB throughout the period of the study suggests total body deficit of bicarbonate (HCO 3 -), leading to respiratory alkalosis and the potential of subsequent metabolic acidosis and further stress susceptibility (Collier et al, 2017). (Horsburgh et al, 2013).…”

“…We also emphasize the importance of local responses to small-scale environmental changes as a contributor to trait variations. Table S5 Our findings on body size and stress response variation based on evolutionary and physiological responses are likely to have wider applications for other wild and domestic species and offer insights into stress assessments to predict biological responses to global climate change (Collier et al, 2017;Maloney et al, 2017). In addition, changes in functional traits like body size have significant repercussions for the thermal biology and energetics of ruminants, as body size directly affects energy requisite for maintenance, growth, and production (Mitchell et al, 2018).…”

“…In SCB, this narrow physiological tolerance can result in an accumulated metabolic cost of plasticity and subsequent low fitness (Maloney et al, ). For instance, as high hemoglobin concentration is associated with a high metabolic rate at higher temperatures, driven by high oxygen demand (Portner & Knust, ), the low hemoglobin level in SCB reflects low protection against oxidative damage, making them more vulnerable to stress (Collier et al, ). Likewise, a significantly higher respiratory rate in SCB than DCB throughout the period of the study suggests total body deficit of bicarbonate (HCO 3 –), leading to respiratory alkalosis and the potential of subsequent metabolic acidosis and further stress susceptibility (Collier et al, ).…”

“…For the first time, heat‐tolerant DCB are characterized at physiological, molecular, and phylogenetic levels. Previous studies have shown that heat stress responses encompass a complex network of pathways, even at the cellular level (Collier et al, ; Rabouille & Alberti, ; Savolainen et al, ). We describe heat stress response quantitatively, differentiating adaptive and plastic changes in response to temperature increase, and revealing different thermoregulatory strategies in different breeds of dwarf cattle.…”

“…As we cannot predict all traits that may in future be advantageous, the conservation of biodiversity within domestic livestock is important, especially in the face of rapidly depleting biodiversity during climate change (Isbell et al, 2015;Mitchell et al, 2018). Moreover, heat stress is becoming an increasingly important constraint on animal productivity in various parts of the world (Collier, Renquist, & Xiao, 2017;Mitchell et al, 2018;Pacifici et al, 2015). Potential solutions for vulnerable populations are to engineer the environment (e.g., controlled environment buildings), which may prove to be unsustainable from an economic, environmental, or animal welfare perspective, or to change/adapt the animal to one that is more suited to the climate (Godfray et al, 2010;Hoffmann et al, 2017;Johnson et al, 2017).…”