The longest bone in a cow's body is the femur, or thigh bone. It plays a crucial role in supporting the animal's weight and facilitates movement by connecting the hip to the knee joint. The femur is an essential component of a cow's skeletal structure, allowing for locomotion and providing attachment points for muscles necessary for walking, running, and grazing. In addition to its functional relevance, the femur can also be a valuable source of bone marrow, which is often harvested for various culinary applications in different cultures.