The
dicarboxylic acids aspartate,
fumarate, and
malate stimulate
lactate utilization by the predominant ruminal bacterium, Selenomonas ruminantium.
Malate stimulates
lactate uptake by S. ruminantium more than does
aspartate or
fumarate, and it seems that
malate and
sodium are involved in stimulating
lactate utilization by this bacterium. Based on the ability of S. ruminantium to grow on
malate in the presence of extracellular
hydrogen and produce
succinate,
malate may be acting as an electron sink for
hydrogen in the
succinate-
propionate pathway used by S. ruminantium. Incorporation of DL-
malate into soluble
starch and cracked corn fermentations with mixed ruminal microorganisms changed final pH, CH4, and VFA in a manner analogous to
ionophore effects. When compared with either
dicarboxylic acids or
monensin alone, dicarboxylic
acid plus
monensin addition to cracked corn incubations stimulated the mixed ruminal microorganism fermentation to produce more
propionate, less
lactate, and increased final pH. Reduced
lactate concentrations in dicarboxylic
acid- and
monensin-treated incubations most likely represents an additive effect of decreased
lactate production by
monensin-sensitive bacteria (i.e., Streptococcus bovis) and increased
lactate utilization by the
monensin-resistant S. ruminantium. The inclusion of
malate as a feed additive into the diets of ruminants is currently not economically feasible; however, forages rich in organic
acids might serve as vehicles for providing
malate to ruminants. When five alfalfa varieties and three bermudagrass hay varieties were surveyed for
malate content, the concentration of
malate in both plant species declined as maturity increased. However, after 42 d of maturity, the concentration of
malate in both forages ranged between 1.9 and 4.5% of the DM. These results suggest that the incorporation of forage varieties that are high in
malate may include
malate economically into the diet and reduce losses associated with ruminal
acidosis.