Genes involved in the thermal tolerance of livestock

Although there is a good amount of knowledge about the physiological aspects, the effects of heat stress at the cellular and genetic level still remain unrevealed. Functional genomics research is providing new knowledge about the impact of heat stress on livestock production and reproduction. Using functional genomics to identify genes that are up- or down-regulated during a stressful event can lead to the identification of animals that are genetically superior for coping with stress and toward the creation of therapeutic drugs and treatments that target affected genes. Given the complexity of the traits related to adaptation to tropical environments, the discovery of genes controlling these traits is a very difficult task. 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 to improve the accuracy and the efficiency of selection for heat tolerance. Studies evaluating genes identified as participating in the cellular acclimation response from microarray analyses or genome-wide association studies have indicated that heat shock proteins are playing a major role in adaptation to thermal stress. Additional genes of interest which two or more studies have identified are the genes for fibroblast growth factor, solute carrier proteins, interluekins, and tick resistance genes. Genes which have only been identified by microarray analysis but not by genome-wide association studies include genes associated with cellular metabolism (phosphofructo kinase, isocitrate dehydrogenase, NADH dehydrogenase, glycosyltransferase, transcription factor, and mitochondrial inositol protein). Other genes of importance were thyroid hormone receptor, insulin-like growth factor II, and annexin.