Melanin as a Multifunctional Molecular System: Biosynthesis, Genetics, and Functional Roles in Livestock Species.

Melanin is the primary pigment found in the skin, hair, wool and feathers of many vertebrates and plays a crucial role in determining the physical appearance and physiological performance of livestock species. Melanin functions in thermoregulation as well as coloration, photoprotection, and adaptation to diverse environmental conditions. This review examines the biosynthesis of melanin and the genetics of melanogenesis in major livestock species such as cattle, sheep, goats, pigs, horses, and poultry, and the roles of melanin-based pigmentation within different systems of animal production. The genetic loci (MC1R, ASIP, TYRP1, TYR, PMEL, MITF, KIT, and others) and polygenic modifiers determine the type and intensity of pigment distribution patterns. Melanin also has a variety of ecological roles, or functions, in addition to economically important traits, affecting adaptation to environmental restraints, product quality, and market preferences. Despite major advances in genomic and transcriptomic studies, many questions still remain, especially in the lack of direct experimental evidence, an insufficient understanding of the physiological roles of melanin in livestock, and a lack of functional validation of key pigmentation genes under production conditions. Future research should focus on bridging these gaps and translating this genetic knowledge to breeding strategies.