Given the advances in technology and mechanization over the past 60 yr and a lack of available data, comparison of fuel requirements between the 2 systems was not possible. Nonetheless, the change in energy requirements incurred by shifting from draft horse to tractor power in the 1944 system was assessed. Energy requirements for a 2-horse team were calculated according to NRC (2007) based on 2 mature Clydesdale geldings under a moderate workload, each with a BW of 800 kg and a daily feed intake equal to 2% of BW. Rations were formulated based on grass hay, rolled barley, and rolled oats, and total cropland area calculated according to the average US crop yields from 1944 for each dietary component (USDA/NASS, 2003). Mechanical energy consumption was based on the maximum power take-off speed (29.6 hp) for a John Deere Series A tractor used in the equation developed for use in the Nebraska Tractor Test (Grisso et al., 2004) at average US usage of 434 tractor-hours/yr (Hertel and Williamson, 1940) and 34.6 MJ/L of gasoline.