If GEI and digestibility are not altered, a decrease in methane production will increase the amount of ME available to the animal, which could increase milk production or body tissue gain (Blaxter and Czerkawski, 1966). In this experiment, methane production was lowered (−28 kJ/kg of BW0.75 per day or 3.4 MJ/d) and apparent NDF, crude fat, and starch digestibility were unaffected by treatment. The conversion of GE into ME was also improved for the nitrate diet. If the energy spared from methanogenesis had been fully converted into milk with an efficiency of 0.64 (NRC, 2001), the increase in milk yield would have been 0.7 kg (milk energy was 3.1 MJ/kg for this experiment). However, no significant increase in milk energy output was observed in this experiment, although milk energy output was numerically higher for the nitrate diet (+6 kJ/kg BW0.75 per day or 0.7 MJ/d).