The contents of phenolic compounds, protein precipitation capacity (PPC) and in vitro gas production of tropical browse species were evaluated. The stoichiometric relationship between in vitro gas measured on incubation of tannin-containing browses in buffered rumen fluid and calculated from short chain fatty acid (SCFA) production was investigated. Crude protein (CP) contents in the browses ranged from 54 to 300 g/kg dry matter (DM). Total phenol (TP), tannins (T) and condensed tannins (TP and T as tannic acid equivalent; CT, as leucocyanidin equivalent) ranged from 17–250, 7–214, and 0–260 g/kg DM respectively, and PPC from 0 to 1066 μg BSA precipitated/g DM. CP content of browses was negatively correlated with TP, T, CT and PPC. A significant correlation was observed between per cent change in gas production on addition of polyethylene glycol (PEG) and the contents of phenolics (r = 0.76 for both TP and T). Addition of PEG to tannin-containing browses increased in vitro gas production. PPC was significantly correlated with TP (r = 0.87; P<0.001), T (r = 0.83; P<0.001), and CT (r = 0.41; P<0.05). A good relationship (R2 = 0.94; P<0.001) was observed between measured in vitro gas production and that calculated from SCFA. The molar proportions of SCFA were not affected by the inclusion of PEG (P>0.05). The relationship between in vitro gas measured on incubation of browse leaves and that calculated from SCFA allows prediction of SCFA from gas production.
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