[In vitro study of ionophore antibiotics and various derivatives. I. Action on fermentation products in the rumen].

An in vitro study was conducted to test the action of different ionophore antibiotics and some of their derivatives on the end-products of rumen fermentation. Nigericin and narasin, like monensin and lasalocid, increased the molar proportion of propionate in the V.F.A. mixture and decreased the proportion of acetate and especially that of butyrate. They had no action on total V.F.A. production. The effect observed with derivatives (lasalocid O-acetyl or nigericin-O-acetyl) was generally less. Gas production, chiefly methane, decreased with the addition of antibiotics. This result agrees with the stoichiometric reactions of carbohydrate fermentation in the rumen. The amount of ammonia nitrogen fixed by bacteria was generally lowered by the addition of five antibiotics (nigericin, narasin, monensin, grisorixin and lasalocid) or two derivatives (lasalocid O-acetyl and nigericin O-acetyl), indicating a decrease in bacterial synthesis. In contrast, calcimycin improved the butyrate production at the expense of propionate, and had no effect on gas composition or bacterial synthesis; X 14547 A and alborixin had only a small effect on rumen fermentations. These results, however, must be interpreted with care since the inocula used came from non-adapted sheep.