Horse Hoof Trimmings as an Untapped Resource for Sustainable Keratin Utilization

Keratin, a structural protein with outstanding mechanical and biochemical properties, is abundant in animal-derived wastes such as feathers, wool, and hooves. However, these keratin-rich materials are still largely incinerated or landfilled, leading to environmental burdens and resource loss. This review introduces horse hoof trimmings as an unexploited, renewable, and cruelty-free keratin source generated through routine equine care. Unlike slaughter-derived materials, hoof trimmings provide a traceable and high-quality biopolymer feedstock with the potential for sustainable valorization. We summarize current knowledge on their chemical composition, structure, and physicochemical properties, highlighting correlations with nutrition, environment, and management practices. Furthermore, we critically assess green extraction methods and upcycling strategies for keratin recovery, identifying challenges and opportunities for scaling toward industrial applications. By focusing on this overlooked waste stream, this review aims to stimulate innovation in sustainable materials chemistry, biopolymer engineering, and circular resource management, advancing the principles of green and circular chemistry.