Wagon de type UIC-I

A refrigerator car (or "reefer") is a refrigerated boxcar (U.S.), a piece of railroad rolling stock designed to carry perishable freight at specific temperatures. Refrigerator cars differ from simple insulated boxcars and ventilated boxcars (commonly used for transporting fruit), neither of which are fitted with cooling apparatus. Reefers can be ice-cooled, come equipped with any one of a variety of mechanical refrigeration systems, or utilize carbon dioxide (either as dry ice, or in liquid form) as a cooling agent. Milk cars (and other types of "express" reefers) may or may not include a cooling system, but are equipped with high-speed trucks and other modifications that allow them to travel with passenger trains. After the end of the American Civil War, Chicago, Illinois emerged as a major railway center for the distribution of livestock raised on the Great Plains to Eastern markets. Transporting the animals to market required herds to be driven up to to railheads in Kansas City, Missouri or other locations in the midwest, such as Abilene and Dodge City, Kansas, where they were loaded into specialized stock cars and transported live ("on-the-hoof") to regional processing centers. Driving cattle across the plains also caused tremendous weight loss, with some animals dying in transit. Upon arrival at the local processing facility, livestock were slaughtered by wholesalers and delivered fresh to nearby butcher shops for retail sale, smoked, or packed for shipment in barrels of salt. Costly inefficiencies were inherent in transporting live animals by rail, particularly the fact that approximately 60% of the animal's mass is inedible. The death of animals weakened by the long drive further increased the per-unit shipping cost. Meat processors sought a method to ship dressed meats from their Chicago packing plants to eastern markets. During the mid-19th century, attempts were made to ship agricultural products by rail.