The effect of tannin with and without polyethylene glycol on in vitro gas production and microbial enzyme activity
The aim was to determine the effect of tannin on the nutritive value and microbial enzyme activity in vitro. The leaves and pods of the Acacia sieberiana and Acacia nilotica trees were subjected to chemical analysis and in vitro fermentation with and without polyethylene glycol (PEG; 35 mg/g). Gas production (GP), true degradability (TD) and the proteolytic and fibrolytic enzyme activities in digesta were determined. Data analyses accounted for the effects of feed type, feed fraction, PEG and their interactions. Leaves and pods had similar NDF and ADF contents in A. sieberiana but differed in both attributes in A. nilotica. The leaves had a higher protein, but lower condensed tannin (CT) contents than the pods. A. sieberiana had more CT than A. nilotica, but both had a similar maximum GP. PEG increased the maximum GP, stimulated GP from the soluble fraction and shortened the lag phase. PEG increased the TD for leaves and pods of A. sieberiana, but suppressed TD in fractions of A. nilotica. PEG also increased the activity of protease enzymes, xylanase, endo- and exocellulases, indicating that tannins depress the digestibility of feeds partly by suppressing the activity of these enzymes. Consequently, condensed tannin depressed the digestibility of feed in the rumen by affecting the activity of enzymes involved in carbohydrate and protein breakdown, the effects of which could be reduced with the use of PEG.
Keywords: Protease, xylanase activity, endo- and exocellulase activity, fibrolase, degradation kinetics, PEG