Laboratory cultured faecal inoculum as a substitute for fresh rumen inoculum for in vitro feed evaluation

This study was carried out to: (1) Preserve whole rumen fluid (RF) or faecal fluid (FF) by culturing using simple techniques; and (2) Study the effect of substituting fresh RF with fresh or laboratory cultured FF as an alternative inoculum source for in vitro fermentation. Faeces and RF were collected from fistulated Jersey cows and cultured (RF or FF with salivary buffer containing maize stover (MS) and lucerne (1:1) at 39°C for three days). For fresh incubation or cultured incubation systems, RF or FF were mixed with salivary buffer containing MS (1 g) and incubated at 39°C for 72 h. True degradability (TD), total gas produced and gas kinetic parameters were determined after incubation. Exocellulase, endocellulase and hemicellulase specific activities (µg reducing sugar/mg crude protein) were assayed. Inocula were alive for 42 days but most active in the first 2 weeks. Cultured FF is a better substitute to fresh RF as shown by its exocellulase activity and TD, compared to differences (P<0.05) observed between fresh RF and FF for exocellulase activity (35 µg glucose/mg protein) and TD (56 g/kg). This study suggests that cultured FF could reduce the cost of experimentation without compromising the reliability of results.   Key words:  Faecal inoculum, cellulases, in vitro fermentation, rumen fluid.