Potency of microbial inocula from bovine faeces and rumen fluid for in vitro digestion of different tropical forage substrates

In vitro ruminal fermentation techniques rely on the availability of fistulated ruminants for rumen fluid (RF), a major constraint for resource-poor institutions. An alternative would be to use faecal microbes. This study was therefore designed to compare the potency of fresh bovine faeces against RF as sources of microbial inocula for fermenting six contrasting tropical forages using the Tilley and Terry (Journal of British Grassland Society, 18, 104111) technique. Faecal inocula were prepared at concentrations of 250 g (Faec250), 300 g (Faec300), 350 g (Faec350), 400 g (Faec400) and 450 g (Faec450) fresh cow faeces per litre bicarbonate buffer. In vitro organic matter digestibility (IVOMD) increased with increasing concentration of faeces at 12-, 24- and 48-h incubation intervals. All faecal inocula except Faec450 had lower potency when compared with RF at all incubation intervals. Digestibility of forage substrates with Faec450 (533 +/- 23 g kg-1 DM IVOMD) was comparable to RF (566 +/- 5 g kg-1 DM IVOMD) after 48-h incubation. Faec450 showed greater potency on more fibrous and low-protein substrates than RF. The coefficient of determination of the regression models for predicting 12-, 24- and 48-h RF IVOMD from Faec450 were 0.914, 0.75 and 0.756 respectively. It was concluded that inocula prepared from 450 g cow faeces demonstrated great potential as a substitute and predictor for RF in 48-h IVOMD assays of tropical forages.