Despite many challenges faced by animal producers, including environmental problems, diseases, economic pressure, and feed availability, it is still predicted that animal production in developing countries will continue to sustain the future growth of the world's meat production. In these areas, livestock performance is generally lower than those obtained in Western Europe and North America. Although many factors can be involved, climatic factors are among the first and crucial limiting factors of the development of animal production in warm regions. In addition, global warming will further accentuate heat stress-related problems. The objective of this paper was to review the effective strategies to alleviate heat stress in the context of tropical livestock production systems. These strategies can be classified into three groups: those increasing feed intake or decreasing metabolic heat production, those enhancing heat-loss capacities, and those involving genetic selection for heat tolerance. Under heat stress, improved production should be possible through modifications of diet composition that either promotes a higher intake or compensates the low feed consumption. In addition, altering feeding management such as a change in feeding time and/or frequency, are efficient tools to avoid excessive heat load and improve survival rate, especially in poultry. Methods to enhance heat exchange between the environment and the animal and those changing the environment to prevent or limit heat stress can be used to improve performance under hot climatic conditions. Although differences in thermal tolerance exist between livestock species (ruminants > monogastrics), there are also large differences between breeds of a species and within each breed. Consequently, the opportunity may exist to improve thermal tolerance of the animals using genetic tools. However, further research is required to quantify the genetic antagonism between adaptation and production traits to evaluate the potential selection response. With the development of molecular biotechnologies, new opportunities are available to characterize gene expression and identify key cellular responses to heat stress. These new tools will enable scientists to improve the accuracy and the efficiency of selection for heat tolerance. Epigenetic regulation of gene expression and thermal imprinting of the genome could also be an efficient method to improve thermal tolerance. Such techniques (e.g. perinatal heat acclimation) are currently being experimented in chicken.

Adaptation to hot climate and strategies to alleviate heat stress in livestock production.

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

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

Buffalo's biological functions as affected by heat stress - A review

Thirty Santa Ines adult, non-lactating, non-pregnant ewes, ten with a brown coat, ten black coated and ten white coated, as well as ten Bergamasca and ten of mixed breed were used to evaluate the effect of climate on physiological and blood parameters in sheep. Two sample collections were taken (6 am and 2 pm) on six days. Sweating rate (SR), heart (HR) and breathing rates (BR), complete hemogram, rectal (RT) and skin temperatures (ST) were measured. Variance analyses were carried out using SAS®. In general, there were significant differences between animals due to skin type, time and day of collection. White coated animals showed lower HR, BR and RT, with afternoon parameters higher than morning. Correlations between HR, BR, RT, SR and ST were medium and positive. Correlations between physiological and blood traits were in general negative and medium. Packed Cell Volume (PCV), total plasma proteins, red blood cell count and hemoglobin concentration had high positive correlations between each other. The first two autovectors explained 49% of variation between traits. White coated Santa Ines animals were shown to be better adapted to climatic conditions in Central Brazil and wool sheep more affected by heat.

/pdf/heat-tolerance-in-brazilian-sheep-physiological-and-blood-14gnwtn4hg.pdf

Heat tolerance in Brazilian sheep: physiological and blood parameters.

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.

Physiological traits as affected by heat stress in sheep—A review

Resumen en: Exposure of sheep to heat stress evokes a series of drastic changes in the biological functions which include decrease in feed intake efficiency and util...

Reproductive performance traits as affected by heat stress and its alleviation in sheep

The application of molecular gene the markers in traits assisted selection are of great significance in improving specific traits of breeds. Currently, there is a great interest in detecting gene-marker alleles that are associated with reproductive and productive livestock traits. To test for possible associations between certain marker gene alleles in Egyptian Suffolk (70-90 % UK Suffolk. 10 – 30 Ossimi sheep; ES) ewes traits, their blood plasma proteins were examined for biochemical polymorphism of Myosin (M), -Galactosidase (-Gal), Phoshorylase  (P), Bovine-serum Albumin (Alb), Catalase (Cat) and Aldolase (Ald) by using-onedimensional sodium dodecyl sulfate polyacrylamide gels electrophoresis (SDSPAGE), with high-range protein molecular weight marker standard as reference bands. Analysis of results indicated clear associations between productive and reproductive traits of heterozygous ewes and marker gene alleles. The associations were highly significant (P<0.01) between Alb marker gene alleles and the highest values of some of the traits studied as follows: A, A and each of age at first lambing and lambs weight at weaning, A, A and fertility (number of lambs born / number of ewes exposed during the breeding season) and A, A and lambing interval. Alb alleles A, A & A, A and A, A were significantly (P<0.01) associated with the youngest age at first lambing, fertility and lambing interval, respectively. The -Gal alleles G,G and Cat C,C were insignificantly associated with the highest values of lamb weight at birth and kilograms of lambs weaned / ewe / season (kilograms of lambs weaned / ewe / season combine the output of group of traits: lambing rate, milk yield, growth rate and pre-weaning mortality). Meanwhile, -Gal alleles G, G were insignificantly associated with the lowest lamb weight at birth. The Cat alleles C, C were insignificantly associated with the lowest of each lamb weight at weaning and kilograms of lambs weaned / ewe / season. The present results may suggest that marker assisted selection could be carried out at a very early age depending on marker gene types for improvement of Egyptian Suffolk sheep traits. This is due to the fact that marker genes could be scored at very early ages.

A. Fadiel

Papers

Physiological traits as affected by heat stress in sheep—A review

Reproductive performance traits as affected by heat stress and its alleviation in sheep

Marker gene alleles associated with Egyptian Suffolk ewe traits.