Comparison of bovine rumen liquor and bovine faeces as inoculum for an in vitro gas production technique for evaluating forages

Two experiments were undertaken using the in vitro gas production technique of Theodorou et al, [Anim. Feed Sci. Technol. 48 (1994) 185] to compare ru men liquor (RL) and faeces (FA) as inocula for fermenting gramminaceous for ages over 96 h periods. Experiment 1 used 12 forages of differing in vivo d igestibility (ammonia treated wheat straw, field-cured hay (Lolium perenne) and 10 artificially dried grasses (L. perenne) harvested at different matu rities). Experiment 2 used seven maize-silage based forages (whole plant, s tover, leaf, lower stem, middle stem, upper stem and husk). In both experim ents, rumen liquor and faeces were obtained from two cows in early lactatio n, each fed daily with 9.4 kg DM of grass silage and 9.0 kg DM of concentra te. Rumen contents were sampled through the fistula, before morning feeding ; faeces were sampled from the rectum, immediately afterwards. Rumen liquor (250 mi) was prepared by straining contents through two layers of muslin, adding the solids after blending with 250 mi of buffer and re-straining. Fa eces were prepared by mixing (300 mi) with 150 mi of buffer and straining t hrough two layers of muslin and adding a homogenate of the solids and 150 m i of buffer after straining. Data were fitted to the model of France et al. [J. Theor. Biol. 163 (1993) 99]. All model parameters showed FA to have a poorer fermentation capacity than RL. In both experiments, potential gas pr oduction volumes (A) were lower ton average 52.9 mi (18.5%)) and lag times longer ton average 2.9 h) for FA compared to RL. Fractional rate of ferment ation at half asymptote (T/2) was generally greater for RL than FA (overall means, 0.042, 0.028) and the time required to T/2 being less (overall mean s, 21.9, 35.4 h). However, potential gas production (A) was highly correlat ed between RL and FA: Experiment 1 (r(2) = 0.94, 11 forages, excluding ammo nia treated straw) and Experiment 2 (r(2) = 0.83, six forages, excluding mi ddle stem). In Experiment 1, organic matter digestibility in vivo (OMDIV) w as also highly correlated with both OMDFA (r(2) = 0.77, 11 forages) and OMD RL (r(2) = 0.89, 11 forages); OMDRL and OMD, were also highly correlated (r (2) = 0.81). Similar correlations occurred in Experiment 2. It is concluded that faeces have potential as an alternative inoculum to rumen liquor for in vitro gas production techniques, but methods of overcoming the longer la g phase with faeces require further research. (C) 2001 Elsevier Science B.V . All rights reserved.