Effect of sugars and malate on ruminal microorganisms.

The objective of this study was to examine the effects of a commercial feed supplement that contains sugars and malate on lactate fermentation by Selenomonas ruminantium grown in batch culture. Experiments also were conducted to examine the effects of this feed supplement on the mixed ruminal microorganism fermentation of ground corn and soluble starch in the presence and absence of 5 mg/kg of monensin. When S. ruminantium strains HD4 and H18 were incubated in basal medium that contained DL-lactate, some DL-lactate was utilized by both strains after 24 h. In the presence of 1 g/L of sugars plus malate commercial feed supplement, both strains used most of the carbohydrate associated with the feed supplement between 6 and 8 h, and lactate was the main end product. In ground corn fermentations by mixed ruminal microorganisms, 2.25 and 3.25 g/L of sugars plus malate commercial feed supplement increased concentrations of acetate, propionate, and total volatile fatty acids, while 3.25 g/L increased lactate and decreased final pH and butyrate. Fermentation of soluble starch in the presence of both concentrations of sugars plus malate commercial feed supplement increased concentrations of acetate, propionate, and total volatile fatty acids and decreased the acetate:propionate ratio. In the presence of 5 mg/kg of monensin, sugars plus malate treatment increased concentrations of propionate and total volatile fatty acids in ground corn and soluble starch fermentations. Collectively, these results suggest that the sugars plus malate commercial feed supplement stimulates the ruminal fermentation.