[In vitro simulation of rabbit cecal fermentation in a semi- continuous flow fermentor. III. Effect of the quantity of dry matter introduced daily in the fermentor and reproducibility of the method].

In a preliminary experiment, 3 Rusitec-like fermentors of 1 L capacity were operated under identical conditions. The only difference was the quantity to treated substratum introduced daily into each fermentor: 15 g/d (M15); 40 g/d (M40); and 60 g/d (M60) on a dry matter basis. The fermentation substratum was a rabbit feed that had been digested with amylase and pepsin. The organic matter was lost over 48 h at a significantly higher rate in the M15 fermentor than in M40 and M60: 30.4%, 19.7% and 17.3%, respectively. The pH values observed in M40 and M60 (5.99 and 5.83) were similar to that observed in vivo under ad libitum feeding conditions. The pH was higher in M15 (6.7), as observed in vivo with restricted animals just before the daily meal. The volatile fatty acids (VFA) proportions for C2, C3 and C4 were similar to the in vivo proportion for the 3 fermentors. The daily total VFA production was the largest with M40 but was associated with a poor stability and an excess of minor VFAs. The introduction of 15 g/d was preferred by the authors because of organic matter disappearance rate, pH stability and VFA production. In a second experiment, 4 fermentors were used in the same way as the M15 one, in order to study the reproducibility of the method. Small but significant differences between fermentors were observed for all parameters in relation to a high fermentor stability from 1 day to the next.(ABSTRACT TRUNCATED AT 250 WORDS)