LAUSR

Abstract Condensed tannin (CT) of varying molecular weights (MWs) may affect rumen microbial fermentation by shifting composition of fungal community. In this study the effects of unfractionated CTs (F0) and CT fractions of different MWs (F1 > F2 > F3 > F4 > F5) from Leucaena leucocephala hybrid-Rendang (LLR) on the fungal mass and composition of fungal community were determined using molecular approaches. The results showed that the total fungi biomass decreased (p < .05) with the addition of higher-MWs CT fractions F1, F2 and F3 with values 35.3 µg/mL, 34.6 µg/mL and 39.3µg/mL, respectively, when compared to that of the control sample (without CTs) at 52.1 µg/mL. Sequencing of the polymorphic internal transcribed spacer 1 (ITS-1) by high-throughput sequencer, recovered mean of 109,190 sequences per-sample which comprised of a number of operation taxonomy units (OTUs) ranging from 22 to 38 and were classified into 7 genera. Piromyces 4 was the dominant genus in the control representing ∼70% of the sequences. Relative abundance of the Piromyces 4 increased significantly (p < .05) with increasing MWs of the CT fractions, however the second dominant Neocallimastigaceae was significantly (p < .05) reduced. This study demonstrated that CT fractions of different MWs could decrease the population mass as well as alter the rumen fungal community structure and diversity, and the effect was more pronounced for higher-MWs CTs. Hence, the shift in fungal diversity, accompanied by changes in population mass would influence fibre digestibility in the rumen in the presence of high MW CTs. HIGHLIGHTS Condensed tannins (CTs) of different molecular weights (MWs) alter the rumen fungi population and diversity. Relative abundance of the Neocallimastigaceae decreased with increasing MWs of CTs, whereas the predominant Piromyces was significantly increased. Higher MWs of CT fractions would influence fibre digestibility in the rumen.