Energy is the first-limiting nutrient of grazing production systems and efficiency in metabolizable energy (ME) utilization needs to be improved, this demands more information about energy cost of grazing. The aim of this study was to estimate the increment above idling in energy expenditure (EE) when Holstein cows were grazing. Multiparous cows (n = 15; fall calving, 2.6 ± 0.1 BCS and 568 ± 55 kg BW) were assigned to 2 feeding strategies: cows grazing a Medicago sativa and Dactylis glomerata mix (21 kg DM/d herbage allowance above 5 cm, 20 h/d) and supplemented with 7.6 kg DM/d of concentrate (18.5% CP; 13 MJ of ME/kg DM) (PMAX; n = 7) and cows grazing a herbage allowance of 9.7 kg DM/d of the same pasture (12h/d) and supplemented with 15.1 kg DM/d of a mixed ration (50:50 ratio forage:concentrate; 18% CP; 10.6 MJ of ME/kg DM) (P30; n = 8). At 98 ± 7 d postpartum, cow EE (O₂ pulse technique) and animal activity (MOOnitor collars, ISR) were recorded simultaneously during 4 consecutive days. The EE for each activity was calculated and compared within each hour of access to the pasture to decrease the effect of DM intake on heat production. Data were analyzed using a mixed model that included feeding strategy as fixed effect and cow genotype as random effect. During access time to pasture, PMAX cows presented a longer (P < 0.01) grazing time (456 vs 202 ± 38 min/d), but a similar herbage intake rate (1.9 ± 0.4 kg DM/h) than P30 cows. Although the EE during idling (1183 vs 1051 ± 44 kJ/BW^0.75/d) and grazing (1251 vs 1117 ± 61 kJ/BW^0.75/d) were greater (P < 0.01) for PMAX than P30 cows, the increase in EE above idling when cows were grazing did not differ (P = 0.85) between feeding strategies (63 vs 58 ± 17 kJ/BW^0.75/d and 5.4 vs 5.7 ± 1.5% for PMAX vs P30).These results demonstrate that the increment in EE above idling for grazing activity did not depend on the inclusion of grazed forage in the diet (63 vs 30% for PMAX and P30) but would probably be associated with bite and intake rate and therefore, to sward structure and mass and animal internal state.