Degradation characteristics and tannin bioassay of some browse forage from Kenya harvested during the dry season

The potential nutritional value of six species of browse forage from Kenya harvested during the dry season were evaluated by chemical composition, in sacco dry matter (DM) degradation and in vitro gas production technique. The effect of tannins on the rumen fermentation of the forage was evaluated using polyethylene glycol (PEG) in an in vitro study. The chemical composition of the species of browse forage differed significantly (P < 0.05). The content of organic matter ranged from 846.7 to 946.5 g/kg DM. The forage had a high crude protein content (155.5-280.9 g/kg DM) and variable content of neutral detergent fiber (NDF, 236.2-682.8 g/kg DM). The content of total extractable tannins was generally low (0.6- 38.5 g/kg DM). At 24 h of incubation, the in sacco DM disappearance ranged from 31.2% to 84.2%. The effective DM degradability also ranged from 29.7 to 73.5%. The gas production after 96 h incubation ranged from 17.5 to 44.2 mL/ 200 mg DM. Use of PEG indicated that tannins had an inhibitory effect on rumen microbial fermentation and this is depen- dant upon the amount and activity of the tannins present. The estimated in vitro organic matter digestibility and metab- olizable energy also increased numerically with the PEG addition. The result of this study indicates that such species of browse forage have the potential to be used as feed supplements for ruminants, especially during the dry season.