Method of polyethylene glycol application to tannin-containing browses to improve microbial fermentation and efficiency of microbial protein synthesis from tannin-containing browses

The effects of application of different amounts of a tannin-complexing agent, polyethylene glycol (PEG, MW 6000) together with different methods of application (addition of PEG at one time as a single dose; or at different times of incubation as split doses) on in vitro rumen fermentation of tannin-containing browses (Acacia albida, Acacia cyanophylla and Calliandra calothyrsus) were investigated. Addition of PEG increased the in vitro gas production, ammonia–nitrogen (NH3–N) concentration and net production of short chain fatty acid (SCFA). The split application of PEG resulted in significantly (P<0.05) higher gas production in A. albida and tended to increase in A. cyanophylla and C. calothyrsus. The method of application of PEG did not affect the SCFA production in A. cyanophylla and A. albida but significantly increased in C. calothyrsus. NH3–N concentration was significantly lower in A. cyanophylla and C. calothyrsus when PEG was applied in the split manner compared to single dose. The split application of PEG resulted in a higher production of microbial protein and a higher efficiency of microbial protein synthesis (EMPS; μmol purines/mmol SCFA) than the single application. This study demonstrated the possibility to improve the efficiency of utilisation of tannin-containing browses using the split application of PEG which improved rumen fermentation resulting from better synchronisation of energy availability and N degradability.