## 4 Discussion  
In this study, the soluble carbohydrate content of HP is low, and the soluble WSC is the key factor for ensilage success. Therefore, it is necessary to make the fermentation substrate have more WSC and establish beneficial bacteria [7]. The PH value is an important index to evaluate the quality of silage. Generally, silage with good fermentation is considered when the pH value is lower than 4.2 [20]. The pH of all treatments in this experiment was lower than 4.2, which met the standard of high-quality silage. The production of LA can rapidly reduce the pH of silage [21]. In this study, the pH value of CE and LP is lower than that of CON and other groups, and the LA content is higher than that of CON and other groups, which indicates that CE and LP have good fermentation effects, and adding LP and CE can promote silage fermentation. [PERSON] et al. (2019) added LP and CE to _Pennisetum_ silage and reached a similar conclusion on pH and LA [22]. It can be considered that cellulase can degrade plant fiber into WSC at the early stage of ensilage, which can promote the reproduction of lactic acid bacteria, resulting in a rapid increase in LA and a decrease in pH [10]. Adding homologous fermentation strains such as LP can ferment silage to produce lactic acid, and the pH value can be reduced compared with untreated silage [23]. Sucrose also solved the problem of insufficient fermentation substrate in silage and promoted the production of LA. However, it is worth noting that in this experiment, when LP and CE were added at the same time, the content of LA decreased and the content of AA increased. The reason may be that cellulolytic enzymes can decompose structural carbohydrates and release pentose. Sugar can be further converted into D-xylose-5-phosphate, and then fermented into a mixture of LA and AA [24]. It may be that more WSC is decomposed by cellulase in the early stages, which leads to the proliferation of _Lactobacillus plantarum_. However, in the later stage, cellulose loses its activity in the low pH environment, and a large number of LPs consume WSC. When sugar is deficient, LP will metabolize LA into AA [25]. The content of AN can reflect the degree of hydrolysis of a polypeptide and the deamination of an amino acid or polypeptide [26]. Compared with CON, the AN content of each treatment group decreased, indicating that the ability of other groups to preserve protein was improved. The presence of butyric acid represents the fermentation of _Clostridium_, which is undesirable in silage [27]. Eating silage with high butyric acid will increase the probability of ketosis in lactating cows [28]. Butyric acid was detected in the  
Figure 3: Heatmap of the top 20 predicted functions (**A**) and pathways (**B**) of the bacterial communities analyzed via PictorSU2 for hybrid _Pennisetum_ silage (CON, control group; CE, 100 U/g FM cellulase addition; LP, \(1\times 10^{6}\) cfu/g FM _Lactobacillus plantarum_ addition; SU, 1% FM sucrose addition). SU group, which indicated that the treatment was contaminated by _Clostritium_, and silage quality decreased. In this experiment, it was found that the DM, NDF, and ADF of other groups all showed different degrees of decline compared with CON. The results showed that silage microbiota decomposed HP to different degrees. The decrease in DM may be due to microbial decomposition of silage nutrients into liquid and gas. [PERSON] et al. (2016) proposed that when heterogeneous fermentation occurs in silage, the consumption of DM will increase, and a large amount of carbon dioxide will be produced [29]. In this study, the CP content of each group added with CE was higher than that of the other groups. This phenomenon may be due to the concentration effect caused by the loss of organic carbon in the fermentation process [30], the protein of the added enzyme, and the effect of cellulase on inhibiting protein degradation and promoting fiber degradation [31].