Design and application of a stratified continuous rumen fermentation system

Two trials were aimed at finding the proper settings of a novel continuous-culture rumen fermenter (CCF) capable of maintaining the protozoa population and reduce the accumulation of undigested materials in the fermentation vessels. The CCF consists of 8 x 2 L glass bottles, warmed at 39°C and placed on a water proof magnetic stirrer. Bottles are closed with a rubber stopper, with an insert for the inflow of artificial saliva, and have the outflow at the base. In Experiment 1 was evaluated the effect of two stirring frequencies (continuous vs intermittent, S1 and S2) and two dilution rates (1.29 vs 1.04) on the pH level and on the counts of the protozoa population in the fermentation fluid. The pH reached a steady state after 4 d of fermentation and S1 bottles had lower pH than those S2 (6.50 vs 6.57, P<0.01). The protozoa in the rumen fluid (from 5.14*10 5 /ml) declined sharply in the first 3 d of fermentation and stabilized at about 13*10 3 /ml in the S2 flasks, while the S1 flasks had lower protozoa concentrations (about 0.8*10 3 /ml, P<0.001). The dilution rates had no effects on pH and protozoa. The Experiment 2 aimed to test the effects of varying the daily feed (F) amount (15, 20, 25, 30 g DM/d of a diet with 50:50 forage: concentrate ratio) on the organic matter (OM) digestibility (OMD) and on the fermentative patterns. In 2 fermentation runs of 8 d each, bottles were inoculated with 450 ml of rumen fluid and 1050 ml of artificial saliva, which was then in flowed at 78 ml/h. Lowering F reduced the OM accumulated inside the vessels (from 5.06 to 0.68 g/d; P<0.0001) but not affected the OMD between dietary treatments (range between 0.460 and 0.510). The reduction of F led to (P<0.001) a linear decrease in volatile fatty acids