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The effect of walking on cattle energy expenditure was assessed by monitoring the CO2 production of cattle with the 14C-entry rate technique. Seven Angus steers (298 +/- 38 kg BW) were peritoneally infused with a solution of NaH14CO3 for 72 hours using portable peristaltic pumps. The steers were forced to walk after 24 hours of infusion, on 2 consecutive days. On the first day, walking was at a constant speed of 2 km.hour-1, divided in 4 periods of 0.5 hours (1 km), first on the level ground, second and third ascending and descending a 6% grade, and finally on the level surface on the way back to corrals. On the second day, cattle walked 1 km at 1 km hour-1, and thereafter walked 4 km at 4 km hour-1 on the level. Saliva samples were collected for periods of 0.5 hours before and during different periods of walking and at rest at 2 and 4 hours after the activity. Concentration and specific activity of CO2 were measured in saliva samples to estimate the rate of CO2 production [ml.hour-1.(BW0.75)-1] as the ratio between the rate of infusion (microCi.hour-1) and the specific activity of CO2 (microCi.liter-1 of CO2). The production of CO2 was converted to heat production using an energy equivalent of 5.26 kcal.liter-1. Average energy expenditure (EE) in corrals in both days before the activity was 82.6 +/- 3.1 kcal hour-1.100 kg BW-1 [650 ml CO2.hour-1.(BW0.75)-1]. The cost of walking on the level surface and on the 6% grade was 9.0 +/- 1.14 and 16.4 +/- 2.18 kcal.km-1.100 BW-1, respectively. There was a small nonsignificant residual effect of walking that disappeared a few hours after exercise. It was concluded that the cost of walking can only have a minor effect on the energy requirement of grazing cattle. The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact lbry-journals@email.arizona.edu for further information. Migrated from OJS platform August 2020