Effects of Long-Chain Fatty Acids on Growth of Rumen Bacteria

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Abstract
The effects of low concentrations of long-chain fatty acids (palmitic, stearic, oleic and vaccenic) on the growth of rumen bacteria [Butyrivibrio sp., B. fibrisolvens, Bacteroides ruminicola, B. succinogenes, Lachnospira multiparus, Ruminococcus flavefaciens, R. albus and Selenomonas ruminantium] were investigated. Except for B. ruminicola and several strains of B. fibrisolvens, bacterial growth was not greatly affected by either palmitic or stearic acids. Growth of S. ruminantium, B. ruminicola and 1 strain of B. fibrisolvens was stimulated by oleic acid; the cellulolytic species were markedly inhibited by this acid. Vaccenic acid (trans .DELTA.11 18:1) had far less inhibitory effect on the cellulolytic species than oleic acid (cis .DELTA.9 18:1). Inclusion of powdered cellulose in the medium appeared to reverse both inhibitory and stimulatory effects of added fatty acids. There was little carry-over effect observed when cells were transferred from a medium with fatty acids to one without. Considerable variation in response to added fatty acids was noted among 5 strains of B. fibrisolvens. In general, exogenous long-chain fatty acids appear to have little, if any, energy-sparing effect on the growth of rumen bacteria.