Perhaps more obviously than other farm types, the dairy farm illustrates the changing technology and practices of farming that occurred during the 20th century. Several trends shaped the evolution of the dairy farm including health regulations and a desire for greater efficiency and scale of farm operations. Health regulations led to changes in interior materials in dairy barns and milk houses to provide washable surfaces. In some cases, regulations also led to demolition of old wood-framed milkhouses and their replacement with concrete block buildings with tile inner walls, while in other cases, the old milkhouse framework was retained and a building that met health standards was built around it. Barn interiors were constructed with easily cleaned materials such as concrete and ceramic tile. Efficiency improvements and increased production led first to the development of barns with open framed hay mows and eventually led to the dominance of the open stall dairy barn in the latter twentieth century.