Intrinsic tannins affect ensiling characteristics and proteolysis of Neolamarckia cadamba leaf silage by largely altering bacterial community
Introduction
Ensiling is a popular and traditional technology of fresh forage preservation. However, extensive nonprotein-N generates due to the effect of plant proteases and microbial activities, which always leads to low N utilization, even economic loss and environmental pollution. It is well proved that tannins could decrease protein degradation during ensiling (Jayanegara et al., 2019, He et al., 2019a) and inhibit the metabolism of microorganisms (Scalbert, 1991), but little information is available about the effects of tannins on silage quality, protease activity and bacterial community during the ensiling. Peng et al. (2018) reported that deactivating condensed tannin by adding PEG at ensiling time led to the increase of protein degradation in Purple Prairie Clover as well as significant changes of microbial communities in terminal silage and upon air exposure, but the dynamic changes of silage fermentation, protease activity and bacterial community during ensiling had not been studied. So far, how tannins alter microbial community to inhibit proteolysis and enhance silage quality is unclear yet, and making it clear would help improve protein preservation in silage production.
Neolamarckia cadamba is a well-known multi-functional plant in tropical and subtropical regions, characterizing fast growth, large biomass yield and rich in bioactive components, and is recently being cultivated as emerging woody forage (Li et al., 2019a, Li et al., 2019b, Pandey and Negi, 2016). Neolamarckia cadamba leaf (NCL) are rich in tannins (hydrolysable tannin >4% dry matter (DM); condensed tannin >6% DM) and macro-nutrients (He et al., 2018), and their dietary inclusion could improve animal growth performance, productivity and product quality (Wang et al., 2017). Furthermore, NCL extract shows strong antibacterial activities on those undesirable bacteria like Bacillus, Escherichia, Staphylococcus, etc., (Khandelwal et al., 2016, Pandey and Negi, 2016), which are common in silage feed. Noteworthily, little proteolysis occurs during NCL ensiling and mixing NCL could dramatically decrease the contents of nonprotein-N and ammonia-N in alfalfa and stylo silage (He et al., 2019b). Given that extensive proteolysis is always an issue for silage production, especially in legume silage, NCL might be an ideal material to investigate the mechanism of protein degradation in silage.
Therefore, this study was conducted to investigate the effects of intrinsic tannins on fermentation quality and protein preservation during NCL ensiling, especially paying attention to protease activity and bacterial community, where tannins were deactivated by PEG addition.
Section snippets
Silage preparation and experiment design
Fresh NCL collected from test field (Guangzhou, China) was manually chopped into 1–2 cm by cutter. In order to investigate the effect of the intrinsic tannins on NCL silage fermentation, polyethylene glycol (PEG 6000) was used to deactivate tannins due to its binding capacity, and the dynamic changes of silage fermentation were studied. In detail, 200 g fresh materials (determined by silo capacity) mixed without or with 11 g PEG (tannins-PEG ratio of 1:2) were ensiled in a mini bag silo
Characteristics of raw Neolamarckia cadamba leaf
As fast-growing woody forage, fresh NCL is normally high in moisture. In the present study, the DM content of NCL (25.11%) was far below 30%–35%, the ideal dry matter content for silage preparation (Guyader et al., 2018), which might favor the activities of plant enzymes and silage bacteria. The same as previous studies, NCL contained a high true protein proportion (88.89% crude protein). Generally speaking, the nutritional value of the crude protein is higher when it contains higher true
Conclusions
The addition of PEG promoted lactic acid fermentation and protein degradation, but inhibited deamination activity and remained a good condition of protein preservation in NCL silage. It also led to remarkable change of bacterial community, where undesirable bacteria such as Methylobacterium were decreased and lactic acid bacteria Leuconostoc and Lactobacillus became the main genus in the PEG treated NCL silage. This study suggests that the intrinsic tannins of NCL affect silage quality by
CRediT authorship contribution statement
Liwen He: Conceptualization, Methodology, Writing - review & editing. Hongjian Lv: Investigation, Data curation, Formal analysis. Yaqi Xing: Resources, Methodology, Investigation. Xiaoyang Chen: Validation, Supervision. Qing Zhang: Conceptualization, Methodology, Visualization.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was financially supported by National Key Research & Development Projects (Grant No. 2017YFD0502102-02), Guangzhou Science Forestry Technology and Innovation Commission (Grant No. 2018KJCX001).
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