Fermentation of a High Concentrate Diet as Affected by Ruminal pH and Digesta Flow

Continuous culture fermentations were conducted to determine the effect of pH and digesta flow rates on fermentation of a 65% grain, 35% forage ration by rumen microorganisms. The pH selected were 5.8, 6.2, 6.6, and 7.0. Imposed on each pH in a randomized complete block design were digesta flow rates of 30/4, 26/8, 22/12. and 18/16, where the first number represents solids retention time (hour) and the second the liquid dilution rate (percent/hour). Microbial efficiency decreased with increasing pH but increased 36% as digesta flow rate increased. The percentage of the microbial population associated with effluent neutral detergent fiber was decreased when pH was reduced below 6.2, which reflects the pattern seen for fiber digestion.