Interaction effect of silo density and additives on the fermentation quality, microbial counts, chemical composition and in vitro degradability of rice straw silage
Introduction
Rice cultivation is the main form of agricultural production in the plain area of South China (Chen et al., 2011). Much of the rice straw is used for biofuel or roughage. In view of the humid and rainy climate in Southern China, ensiling is a feasible processing method for the storage of rice straw. The low water-soluble carbohydrate (WSC) content and lactic acid bacteria (LAB) counts in rice straw prevent the pH from decreasing rapidly, and the pH will not be low enough to inhibit harmful microorganisms (Oladosu et al., 2016). As a result, it is difficult to obtain high-quality silage from rice straw alone (Li et al., 2010).
In a previous study, the use of exogenous LAB was indicated to have good effects on rice straw silage (Gao et al., 2008). At present, most LAB additives used have been mixtures of homofermentative LAB and heterofermentative LAB (Oliveira et al., 2017). Complex LAB additives used in this study were shown to be effective for gramineous crops or grass silages (Liu et al., 2019). There are two ways to improve the WSC content in rice straw. One method is to add cheap sources of exogenous WSC, such as molasses and distiller grains (Yuan et al., 2016). The other method is to degrade cellulose into monosaccharides or oligosaccharides, which can be used by LAB with the addition of cellulose degradation enzymes (Tian et al., 2014). Sufficient WSC not only provides sufficient substrates for lactic acid bacteria fermentation but also increases the nutritional quality of rice straw silage.
The hollow stalk of rice straw is difficult to compact, resulting in a large amount of oxygen remaining in silage during early ensiling which made rice straw silages more susceptible to the negative effects of low silo densities in the actual production process than corn silages (Oladosu et al., 2016). Insufficient compacting density during silage production may lead to air permeability and aerobic deterioration of silage and then lead to the proliferation of yeasts, moulds, and other undesirable microorganisms, thereby increasing the loss of dry matter (DM) and nutrition (Anesio et al., 2017, Sucu et al., 2016). Yeasts, moulds and mycotoxins produced by moulds in rice also have potentially negative effects on animal and human health (Sun et al., 2017).
The studies mentioned above about the effect of additives on rice straw silages were mostly conducted under the condition of high silo density, while few studies have been conducted on whether different additives have effects under the condition of low silo density. On the basis of high silo density, higher density may not have any significant effect on the silage (Yildiz, 2017). It is of great practical significance to select the right additive combination for rice straw silage under several different silo density conditions, and more research is needed on the interaction between silo density and different additives. In this study, the effects of single and combinations of LAB, molasses and enzymes on the fermentation quality, nutritional value, microbial counts and in vitro degradability of rice straw silage with different silo densities were analysed.
Section snippets
Preparation of rice straw silages
The rice (Nanjing 46, hybrid rice supplied by the Institute of Food Crops, Jiangsu Academy of Agricultural Science, Jiangsu, China) was harvested at the full ripening stage at the experimental station of the Jiangsu Academy of Agricultural Science in November. The rice straw was obtained after threshing and cut to 1 cm using a guillotine cutter. The additive was evenly sprayed onto the rice straw, and the DM content was adjusted to 33.75% fresh matter (FM) (original DM content of rice straw was
Raw materials of rice straw
The WSC (6.86% DM) content of rice straw materials in our study was suitable for silage fermentation (Woolford and Pahlow, 1998) and was much higher than that reported (1.59% DM) in the study of Li et al. (2017), but similar to that reported (6.38% DM) in the study of Zhao et al. (2019). Study of Dong et al. (2012) have shown that there were significant differences of non-structural carbohydrates including soluble sugars and starches in rice straw among different varieties. The combination of
Conclusions
The quality of rice straw silage was determined by the characteristics of raw materials, silo density and additives. The use of the M or E group alone is risky for rice straw silages. L. buchneri is active at 300 kg/m3, while L. plantarum and L. paracasei gradually take the lead with increasing silo density. The use of complex additives, E + LAB, further improved the IVDMD, IVNDFD and IVADFD of rice straw silages. It is important to select compound additives according to the raw material and
CRediT authorship contribution statement
Jipeng Tian: Methodology, Investigation, Formal analysis, Writing - original draft. Nengxiang Xu: Methodology, Data curation, Resources, Investigation. Beiyi Liu: Resources, Investigation. Hailin Huan: Resources, Investigation, Validation. Hongru Gu: Methodology, Writing - review & editing. Chenfei Dong: Methodology, Writing - review & editing. Chenglong Ding: Conceptualization, Methodology, Project administration, Funding acquisition.
Acknowledgment
This work was financially supported by the Agricultural Innovation Fund of Jiangsu Province (grant no. CX[17]3037).
Declaration of Competing Interest
Authors declare that they have no competing interests.
Ethical approval
This article does not contain any study with human participants or animals reported by other authors.
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