Abstract
Effect of monensin on postprandial changes of rumen fermentation was studied using four steers by a switch-back trial with three weeks of each period. Steer was fed 2kg concentrate and 10kg grass silage twice daily. In monensin-added group, the steer fed a concentrate supplied with 40ppm monensin. On the last day of each period, rumen fluids were taken through rumen fistula at 0, 1, 2, 4, 6hr after feeding and served for analysis. 1) Protozoal numbers were reduced by 50-60% after feeding due to the addition of monensin, although genus compositions were not affected. The patterns of postprandial changes of protozoal numbers were nealy the same in both groups, in which protozoal numbers decreased immediately after feeding and gradually increased thereafter. 2) Osmotic pressure of the rumen fluids increased in all steers after feeding and that in monensin-added group was lower than that in monensin-free group. 3) Ammonia-N concentration attained a peak at 1hr after feeding in all steers. The concentration during 1-6hr after feeding was decreased by 50-80% by monensin.4)Methylamine-N concentration attained a peak at 4hr after feeding in all steers. The concentration at 4 and 6hr after feeding was decreased by 74 and 50%, respectively, by monensin. 5) VFA concentration tended to be low in monensin-added group. Molar proportion of propionic acid increased and that of butyric acid decreased by monensin. That of acetic acid was not affected.
