Adaptation Mechanisms of Small Ruminants to Environmental Heat Stress

SIMPLE SUMMARY: Heat stress is an intriguing factor that negatively influences livestock production and reproduction performance. Sheep and goat are among the livestock that can adapt to environmental heat stress via a combination of physiological, morphological, behavioral, and genetic bases. Sheep and goat are able to minimize adverse effect of high thermal stress by invoking behavioral responses such as feeding, water intake, shade seeking, and increased frequency of drinking. Their morphological mechanisms are comprised of body shape and size, light hair color, lightly pigmented skin, and less subcutaneous fat, and the physiological means are that of increased respiration rate (RR), increased sweating rate (SW), reduced metabolic rate, and change in endocrine function. Adaptation in terms of genetics is the heritable trait of animal characteristics which favor the survival of populations. For instance, genes like heat shock proteins 70 (HSP70) and ENOX2 are commonly expressed proteins which protect animals against heat stress. ABSTRACT: Small ruminants are the critical source of livelihood for rural people to the development of sustainable and environmentally sound production systems. They provided a source of meat, milk, skin, and fiber. The several contributions of small ruminants to the economy of millions of rural people are however being challenged by extreme heat stress difficulties. Heat stress is one of the most detrimental factors contributing to reduced growth, production, reproduction performance, milk quantity and quality, as well as natural immunity, making animals more vulnerable to diseases and even death. However, small ruminants have successfully adapted to this extreme environment and possess some unique adaptive traits due to behavioral, morphological, physiological, and largely genetic bases. This review paper, therefore, aims to provide an integrative explanation of small ruminant adaptation to heat stress and address some responsible candidate genes in adapting to thermal-stressed environments.