A comparison of recent results with low and high NFFS inclusion rates demonstrates this point. Yang and Beauchemin (2007) used primarily traditional forages and concentrates at different proportions and cut lengths to generate diets with a range of peNDF values. One finding from the study was that peNDF (the proportion of particles retained by a 8-mm sieve multiplied by dietary NDF content) was a much better predictor of ruminal pH dynamics than peNDF (Yang and Beauchemin, 2007); however, despite having one diet with a peNDF of just 9.6% of DM, milk fat yield was maintained across all treatments.