The energy cost of exercise of four pigs (two gilts and two barrows) was determined at liveweights of 30–40 and 60–70 kg using an open circuit respiratory system for measuring oxygen consumption during exercise on a treadmill. Animals were exercised at treadmill belt slopes of +4°, 0° and −4° with the treadmill operated at speeds of 1 and 2 km/h (lighter weight) and 2 and 3 km/h (heavier weight). Increase over resting in energy expenditure during exercise was greater, and less, respectively, at +4° and −4° than at 0°. There were significant differences between animals in both resting energy expenditure levels and in the increment of energy expenditure associated with exercise. Within each liveweight range, the apparent cost of horizontal locomotion increased slightly with an increase in belt speed. The overall estimate of 0.64 cal/hor. kg m is similar to values reported for other species. Cost of vertical work (cal/vert. kg m) was significantly lower at 1 km/h than at 2 km/h at the 30- to 40-kg liveweight range. There was no significant effect of speed on the energy cost of vertical work at 60–70 kg. The overall estimate for the cost of vertical work was 5.27 cal/vert, kg m, which represents an efficiency of 44.4%.
