## 4 Discussion  
The sweet sorghum and Napier grass used in this study contains relatively low DM, WSC and crude protein. According to [PERSON] _et al._[36] forages with insufficient fermentable substrate or too low dry matter content have a FC of < 35, which indicate difficulty in the preservation of the biomass as silage. In the present study, the FC of both grasses was less than 35 and WSC/BC ratio was less than 3, therefore demonstrating the necessity of LAB addition. The DM is one of the most important factors for ensuring the success of the ensiling process [37], the optimal DM content for grasses was determined to be ranging between 350-400 g/kg [38]. In present study both grasses had a DM less than the ideal range and the LAB treatments had a minor effect on DM, NDF and ADF which was in close consent to the results achieved by [39; 40]. It is well known that, a good preserved silage characterized by low pH, according to [41] rapid acidification reduces the risk of undesirable microorganism growth during the early stage of ensiling therefore the rate of pH decline may be more important than the final pH. In this study, the pH of all treated batches continued to reduce the pH from the start till the end of the experiment and this finding in consistent with [42]. The more rapid pH decrease when adding the LAB inoculant provide a clear indication regarding its role in the fermentation process stimulation. As the inoculants reduced the pH from 5.76 to 3.9 in sweet sorghum and Napier grass from 5.97 to 4.9 in first 5 days of ensiling, the reduction was commensurately with the LA produced. This findings are in agreement with [43], the faster reduction in pH is correlated with the high LA content which would further lead to improved nutrients preservation. [PERSON] 2015, also found high LA when applied _Lactobacillus_ spp in total mixed rations among other chemicals [44]. As the previous studies mentioned, the addition of LAB inoculants at ensiling is intended to ensure rapid and vigorous fermentation [45]. As previously mentioned by [3] using LAB to enhance silage quality by significantly improving the lactic acid concentration of silage, which is compatible with the present results, when the high LA concentration is produced by incubated LAB than control and commercial bacteria. On another hand, untreated sweet sorghum batch produced a lower amount of WSC this may due to the efficiency of epiphytic LAB to convert sugars and his results can be supported by the outcomes of [PERSON] (2015), mixed the sweet sorghum with alfalfa which revealed a pH decline [46]. However, all strains isolated in currant study were a homofermatterative LAB those bacteria are preferred during the ensiling process, because of their ability to rapidly convert forage sugars to lactic acid, which has a high acidifying potential [3]. The other organic acids AA, BA and PA were produced when the undesirable bacteria fermented the WSC [47; 48] and they are considered not desirable because of their a negative effect on the voluntary intake [49]. In this study, the LAB inoculant succeeded to reduce the amount of these acids which may occur due to restricting the vigour of undesirable microorganisms. This results were in agreement with [50], who reported that, soybean silage inoculated with L. _plantarum_ showed an acceptable reduction on AA and BA. The fermentation process mainly depends on the availability of microorganisms in the silage, the water content of the crop and the type of substrate available for fermentation [51]. In our study, the pH and WSC decreased on both treated and untreated grasses and this result agrees with previous studies by [34]. The fast decline in WSC content and high production of LA in the first 5 days of ensiling could indicate by the ability of LAB to inhabit the other microorganisms. In this point, previously reported that, in addition to LAB, some other microorganisms in the fermentation process compete for available nutrients [52].