Bacterial direct-fed microbials in ruminant diets: Performance response and mode of action

Abstract

Direct-fed microbials (DFM) have been shown to increase daily gain and feed efficiency in feed- lot cattle, enhance milk production in dairy cows, and improve health and performance of young calves. How- ever, their effects on performance have been mixed, and the mode of action remains unclear. Bacteria used as DFM have been defined as single or mixed cultures of live organisms, which, when fed to animals, beneficially affect the host. The original concept of feeding DFM to man and livestock was based primarily on the potential for beneficial intestinal effects, including the establish- ment of a desirable gut microflora and/or prevention of the establishment of pathogenic organisms. More re- cently, however, there has been some indication that certain bacterial DFM might have beneficial effects in the rumen, such as decreasing the potential for ruminal acidosis. In several experiments, supplementing feedlot cattle with lactate-utilizing and/or lactate-producing bacteria has been shown to improve feed efficiency and daily gain (approximately 2.5%), with little change in DMI. In addition, increased milk yield (0.75 to 2.0 kg/