Effect of Molasses, Corn Meal, or a Combination of Molasses plus Corn Meal on Ruminal Fermentation of Orchardgrass Pasture During Continuous Culture Fermentation

Although molasses is being used by dairy farmers, particularly certified organic dairies, as a lower cost energy alternative to corn, little research currently exists evaluating the effects of molasses as the sole supplement on the ruminal fermentation of grazing dairy cows. This study evaluated the effects of pasture supplementation with molasses, corn meal, or a combination of molasses and corn meal, on ruminal nutrient digestibility and bacterial N synthesis in continuous culture fermenters. Experimental treatments were 1) orchardgrass (Dactylis glomerata L.) pasture only (control; 70 g DM/d); 2) molasses plus orchardgrass pasture (MOL; 3.5 g DM/d of molasses plus 66.5 g DM/d of pasture); 3) corn meal plus orchardgrass pasture (CM; 4.9 g DM/d of corn meal plus 65.1 g DM/d of pasture); and 4) molasses plus corn meal plus orchardgrass pasture (MOL + CM; 3.5 g DM/d of molasses plus 4.9 g DM/d of corn meal plus 61.6 g DM/d of pasture). Treatment did not affect (P > 0.05) apparent DM, OM, and NDF digestibility values; true DM and OM digestibility values; molar proportions of VFA; or acetate-to-propionate ratio. Mean ruminal pH tended (P = 0.071) to be greater for MOL. Maximum ruminal pH was greatest (P < 0.05) for MOL. Ruminal NH3-N was lowest (P < 0.05) for MOL + CM. Crude protein digestibility was greatest (P < 0.05) for MOL and lowest for MoL + CM. Bacterial N flow (g/d) and efficiency of bacterial N synthesis were not affected (P > 0.05). At low levels of inclusion, molasses showed results similar to corn meal in improving ruminal fermentation and N utilization, with both supplements showing only minimal improvement compared with a pasture-only diet.