Schlau, N., Duineveld, L., Yang, W. Z., McAllister, T. A. and Oba, M. 2013. Precision processing barley grain did not affect productivity of lactating dairy cows. Can. J. Anim. Sci. 93: 261-268. This study evaluated the effects of precision processing (PP; processing based on kernel size) barley grain on ruminal fermentation and productivity of lactating dairy cows. Twenty multiparous Holstein cows, including eight ruminally cannulated cows, were used in a replicated 4×4 Latin square design with 21-d periods. Diets contained light barley grain processed precisely using a narrow roller setting (LB), heavy barley processed precisely using a wide roller setting (HB), processed HB and LB mixed at equal proportions (PP), or equal parts of light and heavy barley grain processed at a single narrow roller setting (CON). All diets consisted of 40% barley grain, 40% barley silage, and 20% of a supplement premix. Comparisons were made between LB and HB to evaluate the effect of barley quality, and between PP and CON to evaluate the effect of precision processing. Dry matter intake, sorting index, ruminal fermentation characteristics, and nutrient digestibility were not affected by diet. In addition, milk yield and concentrations of milk fat, protein, and lactose were not different, although milk urea nitrogen concentration was greater for PP vs. CON and for LB vs. HB. These results suggest that precision processing barley grain based on kernel size may not drastically affect ruminal fermentation and milk production in lactating dairy cows.