Abstract
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.
Highlights
Most in vitro digestibility studies rely on the fermentation of feed using buffered rumen fluid as an inoculum (De Boever et al 2005; Menke et al, 1979; MirzaeiAghsaghali et al, 2007; Prates et al, 2010; Stern et al, 1997; Tilley and Terry, 1963)
Fresh rumen fluid (RF) specific activity was higher than that observed in faecal fluid (FF) (Table 1)
Faecal inoculum is a potential substitute of rumen inoculum for in vitro feed evaluation as demonstrated by the small differences observed in their true digestibility and gas production
Summary
Most in vitro digestibility studies rely on the fermentation of feed using buffered rumen fluid as an inoculum (De Boever et al 2005; Menke et al, 1979; MirzaeiAghsaghali et al, 2007; Prates et al, 2010; Stern et al, 1997; Tilley and Terry, 1963). This is because rumen inoculum has been found to yield results which mimic those from in vivo studies (Brown et al, 2002; Gizzi et al, 1998). While many studies engage in comparing rumen and faecal inoculum incubations of the same animals (ElMeadaway et al, 1998; Váradyová et al, 2007), others compared faecal inocula from ruminants and hindgut fermenters (Denek and Can, 2007; Denek et al, 2008). Denek and Can (2007) reported that buffered faecal
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