Testing a stratified continuous rumen fermenter system

The capability of maintaining protozoa populations and reduce the accumulation of undigested material was investigated in two experiments using a stratified continuous-culture rumen fermenter (CCF) at various setting. 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 the effect of two stirring frequencies (continuous vs intermittent, S1 and S2) and two dilution rates (D, 1.29 vs 1.04) on the pH values and on the counts of the protozoa in the fermentation fluid was evaluated. 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<0.001). The protozoa in the fermentation fluid (2.92*105/ml at the beginning) declined sharply in the first 2 d of fermentation and stabilized at about 13*103/ml in the S2 flasks, while the S1 flasks had lower protozoa concentrations (about 0.8*103/ml, P<0.001). The D had no effects on pH and protozoa. Experiment 2 aimed to test effects of varying the daily diet (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 pumped at a rate of 78 ml/h. Lowering F reduced the OM accumulated inside the vessels (from 5.06 to 0.68 g/d; P<0.001) but did not affected the OMD for any of the dietary treatments (range between 0.460 and 0.510). The reduction of F led to a linear decrease (P<0.001) in volatile fatty acids concentration (from 65.8 to 45.3 mM), to an increase of acetate:propionate ratio (from 2.91 to 3.42) and to a reduction of pH (from 6.4-6.5 to 6.0-6.1). Lowering F tended to increase the number of protozoa (from 72 to 198*103/ml, P=0.082). The tested CCF reaches stable conditions of fermentation after some days of adaptation, allows the survival of protozoa population and has a limited accumulation of undigested materials in the glass bottles.