Adaptive assessment of small ruminants in arid and semi-arid regions

•This manuscript provides deep understanding of the various impacts of heat stress on small ruminant production and climate adaptation.•The review presented possible phenotypic markers for the inclusion on evaluation of more adapted animals.•We suggest the inclusion of immediate and subsequent responses on the adaptive assessment of animals. Breeding small ruminants is an important economic activity in arid and semi-arid regions. This activity has gained more prominence in the present climatic scenario. With increasing global warming, many researchers are analysing how locally adaptive animals maintain homeostasis in regions characterized by high air temperatures. However, there has been no standardization regarding which characteristics should be assessed to determine the adaptive capacity of these animals or included in breeding programmes to improve thermal resistance. Thus, the objectives of this review are: (1) to present an overview of characteristics involved in heat adaptation of highly adapted small ruminants and (2) highlight the characteristics that could be included in breeding programmes to increase the adaptability of herds. Much research has evaluated the immediate response of animals to thermal stress conditions, such as increases in rectal temperature, respiratory rate, and sweating. However, considering that homeostasis represents a condition of balance in a biological system and that animals adapted to the environment are in homeostasis, this review proposes to address the adaptive characteristics acquired over years of exposure to stressful conditions in arid and semiarid regions. These include morphological changes such as coat characteristics, alterations in blood constituents, acid-base balance, such as hormones, haematological and biochemical profiles, as well as advances in genetic assessments.