In previous studies with sheep (Nolan et al., 2010; van Zijderveld et al., 2010), the dietary inclusion of nitrate was higher than that in the current study (24 and 26 g of nitrate/kg of DM in the respective sheep studies compared with 21 g of nitrate/kg of DM in the current study). However, when expressed relative to metabolic BW, the nitrate dose in the current experiment was considerably higher than in our previous study with sheep (3.4 g of nitrate/kg of BW0.75 per day vs. 1.6 g of nitrate/kg of BW0.75 per day for dairy cows and sheep, respectively). This higher dose may have led to a higher proportion of the dietary nitrate entering the blood through the rumen wall and being lost in urine. This could be another explanation for the relatively higher efficiency of methane abatement with dietary nitrate in sheep.