EFFECTS OF THE IONOPHORE ANTIBIOTICS MONENSIN, MONENSIN-PROPIONATE, ABIERIXIN AND CALCIMYCIN ON RUMINAL FERMENTATIONS INVITRO (RUSITEC)

The effects of four chromatographically purified ionophore antibiotics (purity > 98.5% were studied on rumen fermentation using a semi-continuous system (Rusitec). The microbial population of the fermenters originated from the rumen of sheep fed a basal ration of hay without added antibiotic. Each day, 2 mg of feed-incorporated ionophore were added to the fermenter. Monensin A and monensin-propionate, prepared from monensin A by esterification of the alcohol function at C26, (Type I) both reduced the plant cell-wall degradation of dehydrated alfalfa. They also modified the orientation of fermentation towards an increased production of propionate at the expense of acetate and butyrate, and a decreased methanogenesis. Abierixin (Type II) slightly reduced degradation of the ADF fraction of alfalfa and induced a pronounced accumulation of ammonia nitrogen in the effluents. Calcimycin (Type III) had no real effect on digestion and fermentation. Because of elimination of most of the protozoa from the Rusitec at the end of the first week, corresponding to the adaptation period, we could not study the effect of antibiotics on rumen ciliates. The behaviour of these compounds is discussed in relation to their ionophore properties and their antibiotic activity. © 1990.