Effect of Replacing Total Mixed Ration with Pasture on Ruminal Fermentation

Mixed cultures of ruminal microorganisms were used to examine the fermentation profile of diets (DM basis) consisting of 1) 100% TMR, 2) 85:15 TMR:pasture, 3) 70:30 TMR:pasture, and 4) 55:45 TMR:pasture. The pasture portion of the diets consisted of annual ryegrass harvested at a height (5 to 7 cm) that simulated animal grazing. The proportion of forage (silage in TMR plus pasture) to concentrate ranged from 40:60 (100% TMR) to 67:33 (55:45 TMR:pasture). Increasing the proportion of dietary pasture increased total dietary soluble protein, forage, and total diet digestibility (P < 0.01) and decreased (P < 0.001) ruminal methane. Increased forage from pasture improved ruminal fermentation in a manner consistent with enhanced feed nutrient utilization. Data from this study support the enhanced lactational performance observed with cows fed similar diets in a concurrent study.