Aim: To determine whether Megasphaera elsdenii YE34 (lactic acid degrader) and Butyrivibrio fibrisolvens YE44 (alternative starch utilizer to Streptococcus bovis) establish viable populations in the rumen of beef cattle rapidly changed from a forage-based to a grain-based diet.
Methods and results: Five steers were inoculated with the two bacterial strains (YE34 and YE44) and five served as uninoculated controls. With the exception of one animal in the control group, which developed acidosis, all steers rapidly adapted to the grain-based diet without signs of acidosis (pH decline and accumulation of lactic acid). Bacterial populations of S. bovis, B. fibrisolvens and M. elsdenii were enumerated using real-time Taq nuclease assays. Populations of S. bovis remained constant (except in the acidotic animal) at ca 10(7) cell equivalents (CE) ml-1 throughout the study. Megasphaera elsdenii YE34, was not detectable in animals without grain in the diet, but immediately established in inoculated animals, at 10(6) CE ml-1, and increased 100-fold in the first 4 days following inoculation. Butyrivibrio fibrisolvens, initially present at 10(8) CE ml-1, declined rapidly with the introduction of grain into the diet and was not detectable 8 days after grain introduction.
Conclusion: Megasphaera elsdenii rapidly establishes a lactic acid-utilizing bacterial population in the rumen of grain-fed cattle 7-10 days earlier than in uninoculated cattle.
Significance and impact of the study: The study has demonstrated that rumen bacterial populations, and in particular the establishment of bacteria inoculated into the rumen for probiotic use, can be monitored by real-time PCR.