Livestock plays an important role in the global economy. Climate change effects are not only limited to crop production, but also affect livestock production, for example reduced milk yields and milk quality, reduced meat production and reduced fertility. Therefore, livestock-based food security is threatened in many parts of the world. Furthermore, multiple stressors are a common phenomenon in many environments, and are likely to increase due to climate change. Among these stresses, heat stress appears to be the major factor which negatively influences livestock production. Hence, it is critical to identify agro-ecological zone-specific climate resilient thermo-tolerant animals to sustain livestock production. Livestock responds to the changing environments by altering their phenotypic and physiological characters. Therefore, survivability of the animal often depends on its ability to cope with or adapt to the existing conditions. So to sustain livestock production in an environment challenged by climate change, the animals must be genetically suitable and have the ability to survive in diversified environments. Biological markers or biomarkers indicate the biological states or alterations in expression pattern of genes or state of protein that serve as a reference point in breeding for the genetic improvement of livestock. Conventionally, identification of animals with superior genetic traits that were economically beneficial was the fundamental reason for identifying biomarkers in animals. Furthermore, compared with the behavioural, morphological or physiological responses in animals, the genetic markers are important because of the possibility of finding a solution to animal adaptability to climate change.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/B4C14198D392C6548D162B540A524093/S1751731118001945a.pdf/div-class-title-review-adaptation-of-animals-to-heat-stress-div.pdf

Review: Adaptation of animals to heat stress.

How can heat stress affect chicken meat quality? - a review

We investigated the molecular mechanisms by which chronic heat stress impairs the breast-meat quality of broilers. Broilers were assigned to three groups: the normal control (NC) group, heat-stress (HS) group, and pair-fed (PF) group. After 7 days of heat exposure (32 °C), the high temperature had caused oxidative stress; elevated the activity of citrate synthase (CS), the mRNA expression of M-CPT1, and the phosphorylation level of AMPKα; and reduced the mRNA expression of avUCP. After 14 days of heat exposure, the heat stress had increased the lightness and drip loss and decreased the pH and shear force of the breast meat. Additionally, the heat exposure had increased the mRNA expressions of FAS, ACC, and PDK4; the content of lipids; and the activities of lactic dehydrogenase and pyruvate kinase, and it had decreased the mRNA expression of M-CPT1 and the activity of CS. In conclusion, chronic heat stress impairs meat quality by causing mitochondria to malfunction and affecting energy-substance aerobic me...

Chronic Heat Stress Impairs the Quality of Breast-Muscle Meat in Broilers by Affecting Redox Status and Energy-Substance Metabolism.

The present review is an attempt to signify the importance of heat shock proteins in livestock adaptation during heat stress. The cellular and molecular responses in livestock are very crucial as it may lead to identification of confirmatory biomarker for heat stress in livestock. Thermo-tolerant gene expression and elevated heat shock protein (HSP) levels are observed to be the ultimate response through which the cell survives the heat stress. The HSPs have chaperonic activity ensuring the folding, unfolding and refolding of stress-denatured proteins. The components of heat shock response include heat shock factors (HSFs), heat shock element (HSE) and HSP. The cellular response to heat stress in mammalian organisms is controlled at the transcription level and it is mediated by a family of HSF which are regulated by the corresponding HSF genes. The activated HSFs bind with the HSE in the promoter region of HSP genes culminating in enhanced transcription of HSP mRNA. The HSP70, HSP90 and HSP27 are the predominant HSPs having protective role during heat stress in farm animals. Among these HSPs studied, HSP70 was identified to be the ideal biological marker for quantifying heat stress in animals.

https://medcraveonline.com/JDVAR/JDVAR-05-00127.pdf

Role of Heat Shock Proteins in Livestock Adaptation to Heat Stress

Heat stress often occurs in the modern poultry industry, which impairs growth performance, particularly via reducing appetite. This study was aimed to investigate the mechanism of attenuating appetite by chronic heat exposure in broilers. A total of 144 broilers (28 days old) were allocated to normal control (NC, 22 °C), heat stress (32 °C), and pair-fed (22 °C) groups.; Results: Chronic heat exposure significantly increased cloacal temperatures and respiration rates, decreased the average daily feed intake and average daily gain, increased feed-to-gain ratio compared with the NC group, and elevated the concentrations of ghrelin and cholecystokinin (CCK) both in serum and intestine, as well as peptide YY and somatostatin in intestine on 35- or 42-day-old broilers. Moreover, heat exposure decreased villi height (VH) and the ratio of VH to crypt depth (CD), while it increased CD in the jejunum on 35- and 42 day-olds, increased (P < 0.05) the concentrations of valine and isoleucine in plasma on 42 days, and upregulated (P < 0.05) the expression of taste receptor type 1 members 1 and 3 (T1R1 and T1R3), CCK, and ghrelin in the intestine on 35- or 42-day-old broilers.; Conclusion: Chronic heat exposure impairs the performance, intestinal morphology and appetite, which may be correlated with the increased secretion or gene expression of appetite-related hormones and genes, and the higher expression of nutrient-sensing receptors (T1R1 and T1R3) in broilers. © 2018 Society of Chemical Industry.; © 2018 Society of Chemical Industry.

Effects of chronic heat exposure on growth performance, intestinal epithelial histology, appetite‐related hormones and genes expression in broilers

Elevated ambient temperatures affect animal production and welfare. Animal's reduced production performances during heat stress were traditionally thought to result from the decreased feed intake. However, it has recently been shown that heat stress disturbs the steady state concentrations of free radicals, resulting in both cellular and mitochondrial oxidative damage. Indeed, heat stress reorganizes the use of the body resources including fat, protein and energy. Heat stress reduces the metabolic rates and alters post-absorptive metabolism, regardless of the decreased feed intake. Consequently, growth, production, reproduction and health are not priorities any more in the metabolism of heat-stressed animals. The drastic effects of heat stress depend on its duration and severity. This review clearly describes about biochemical, cellular and metabolic changes that occur during thermal stress in farm animals.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/jpn.12379

I. Belhadj Slimen

Papers

Heat stress effects on livestock: molecular, cellular and metabolic aspects, a review.