EFFECT OF NIGERICIN, MONENSIN, AND TETRONASIN ON BIOHYDROGENATION IN CONTINUOUS FLOW-THROUGH RUMINAL FERMENTERS

Four ionophores differing in cation selectivity were compared for thei r effect on microbial fermentation and biohydrogenation by ruminal bac teria in continuous culture. Monensin and nigericin are monovalent ant iporters with selective binding affinities for Na+ and K+, respectivel y. Tetronasin is a divalent antiporter that binds preferentially with Ca2+ or Mg2+. Valinomycin is a monovalent uniporter and does not excha nge K+ for H+. Steady-state concentrations of 2 mu g/ml of monensin, n igericin, tetronasin, or valinomycin were maintained by constant infus ion into fermenters. Molar percentages of acetate were lower, and thos e of propionate were higher, in the presence of monensin, nigericin, a nd tetronasin; all three ionophores also decreased CH4 production. Con centrations of valinomycin as high as 8 mu g/ml had no effect on volat ile fatty acids or CH4 production. Monensin, nigericin, and tetronasin inhibited the rate of biohydrogenation of linoleic acid. Continuous i nfusion of C18:2n-6 at a steady-state concentration of 314 mu g/ml int o fermenters receiving monensin, nigericin, or tetronasin resulted in lower amounts of stearic acid and higher amounts of oleic acid. Ionoph ores increased total Cl8:2 conjugated acids mainly because of an incre ase in the cis-9, trans-11-C-18:2 isomer. If reflected in milk fat, io nophore-induced changes in ruminal lipids could enhance the nutritiona l qualities of milk.