PREVENTING IN-VITRO LACTATE ACCUMULATION IN RUMINAL FERMENTATIONS BY INOCULATION WITH MEGASPHAERA-ELSDENII

In vitro fermentations containing a mixed culture of ruminal bacteria (ruminal fluid from a hay-fed steer), buffer, and primarily rapidly de gradable substrates (starch, glucose, cellulose, cellobiose, and trypt icase) were inoculated with an overnight culture of Megasphaera elsden ii B159. Triplicate flasks were either uninoculated or inoculated to o btain a final concentration of 8.7 x 10(5) and 8.7 x 10(6) colony form ing units of M. elsdenii per milliliter of culture fluid. Inoculation with M. elsdenii prevented an accumulation of lactic acid and excessiv e drop in pH. Lactate peaked at more than 40 mM in untreated cultures. In cultures inoculated with a low dose of M. elsdenii, lactate concen tration peaked at approximately 25 mM at 5 h of fermentation but decre ased rapidly to less than 5 mM by 7 h of fermentation. With the additi on of the high dose of M. elsdenii, lactate was never greater than 2 m M (P < .05) throughout fermentation. Cultures treated with M. elsdenii had greater amounts (P < .05) of isobutyrate, butyrate, isovalerate, and valerate than untreated cultures. After 24 h of fermentation, one- half of the culture fluid was transferred to an equal volume of fresh buffer with substrate but was not inoculated with further quantities o f M. elsdenii. Six hours after transfer, cultures that had been origin ally treated with M. elsdenii had lower (P < .05) amounts of lactate t han untreated cultures. Inoculation with M. elsdenii has potential to prevent lactate accumulation in diets containing readily fermentable c arbohydrates.