In China, the annual yield of wheat (Triticum aestivum L.) straw is approximately 115.4 million tons [1] . However, about 50% of this abundant crop by-product is deserted directly in the field or burned for cooking, which cause seriously environmental problems [2] . With the rapid development of animal husbandry, feed shortage has become a limiting factor for livestock production [3] . Therefore, it is necessary to develop silage preparation technique to effectively use these local available feed resources for livestock production in China.

Ensilage has long been used to preserve forage crops for livestock. During fermentation process, the epiphytic lactic acid bacteria (LAB) on forage crops utilizes water-soluble carbohydrate (WSC) to produce lactic acid, the primary acid responsible for decreasing the pH in silage [4] -[6] . Silage additives have also been used to obtain high-quality silage, and inoculants and cellulase are the most popular additives on silage [4] . LAB inoculants applied to forage at ensiling promote homofermentation of major WSC transfer to lactic acid, which causes a rapid pH decline [7] . Wheat straw is mainly composed of cellulose, hemicellulose and lignin; hence, its low digestibility prevents the use in feedlots. The addition of cellulase to silage can partially degrade fiber to fermentable WSC used by LAB [8] . The mixtures of inoculants and cellulase had also been used to improve the fermentation quality of silage.

In the present study, we aimed to examine the effect of LAB and cellulose on the fermentation quality and chemical composition of wheat straw silage by using a small-scale fermentation system.

The moisture content of silage material plays an important role influencing silage fermentation, because moisture is required by LAB for metabolic reactions and has a significant effect on the initial level and transport of oxygen during ensilage process [11] . Zheng et al. [12] reported that ensilage quality improved as the moisture content decreased from 80% to 60% for sugar beet pulp silage and from 60% to 45% for tomato pomace silage, and storage at below 30% of FM prevents almost all the microbial activity. However, moisture content of the material used in this study is only approximately 10% of FM which is much lower than the moisture requirement for high-quality silage (usually beyond 50% of FM). Therefore, the moisture of the wheat straw was moderated to 60% of FM by spraying distilled water.

Forages are fermented by a complex consortium of microorganisms, predominantly by LAB which convent WSC into organic acid. As a result, the pH is reduced and the forages are preserved. Generally, when LAB reaches to at least 10⁵ (cfu∙g⁻¹ of FM), silages can be well preserved [13] . However, as shown in Table 2, LAB values 10³ (cfu∙g⁻¹ of FM) present in the fresh wheat straw suggest that certain inoculants should be applied to this silage.

Lactobacilli are the dominant microbial population on forage crops and contribute to the lactic acid fermentation for a longer time than do lactic acid-producing cocci. Usually, L. casei and L. plantarum are found living in association with forage crops and silages [14] [15] . Many studies have shown the advantages of such inoculants [13] , such as adding selected lactobacilli to ensilage forages can dominant or outnumber the epiphytic LAB. At the beginning of fermentation, production of lactic acid by homofermentative lactobacilli is preferred to reduce the pH value, which may inhibit the growth of harmful microorganisms such as mold, coliform bacteria and aerobic bacteria. In the present study, the LAB-treated silages have a relatively low pH at the earlier stage of fermentation, which inhibit the production of n-butyric acid and Ammonia-N. However, in the later days of fermentation, the LAB- and LAB + cellulase-treated silages have lower LAB number than the control (P < 0.05). The plausible reason is that the lower pH prevents the growth of LAB its own. More surprise, the treatment with both two LAB inoculants reduces extents of ADF and NDF in a relative larger level compare to the cellulase treatment. Guan et al. [16] indicated that this may because the enzymes secreted by microbial degrading the crude fiber during fermentation process. Therefore, strains Z3-1 and FG 1 could be used as excellent inoculants for ensiling wheat straw.

Moreover, Sun et al. [17] reported the addition of cellulase increased substrate for LAB from NDF degradation, and propagation of LAB could be promoted in the early stage of ensiling, which resulted in a rapid increase in lactic acid and a drop of pH, so inhibiting activity of harmful bacteria and plant enzymes for proteolysis. However, the efficiency of such enzymatic hydrolysis has been shown to depend on various factors as substrate, environmental conditions and biomass physicochemical pretreatments [18] . That may mean in some cases enzymes cannot significantly reduce the NDF and ADF contents and improve the silage quality. For example, Mandebva et al. [19] and Kozelov et al. [20] found that fibrous enzyme had no effect on cell wall concentration of bermuda grass and lucerne silage, respectively. In the present study, the NDF and ADF values decreased significantly (P < 0.05) in the cellulase-treated silages compared with the control, indicating that the cellulase addition was effectively in degrading the cell wall carbohydrate. Silage treated by cellulase usually can reduce fiber composition and improve the digestibility, and the present experiment also proves the cellulase treatment silage, while raising the quality of fermented, also reduced the fiber composition and hardness of feed. The similar results were also found by Stokes et al. [21] , Shepherd et al. [22] and Sun et al. [3] . However, the CP and lactic acid contents of cellulase-treated silages did not show a significant improvement than control, while the pH values were higher than cellulase + LAB (Z3-1 and FG 1)-treated silages. We consider the main reason of the high CP content of the sample is for the breed, because almost all fields in that area were treated with the same fertilizer cultivation. The results may indicate that the most epiphytic LAB present in the fresh wheat straw were heterofermentative, which could not effectively ferment the substrate provided by cellulase degrading the fiber, therefore, resulting in poor silage; in contrast, as described before, the homofermentative LAB Z3-1 and FG 1 inoculants could utilize the substrate sufficiently and improve the fermentation quality well.

The concentrations of butyric acid and NH₃-N in silages are also important criterions for evaluating silage fermentation quality, and they were usually associated with the activity of clostridia. In this study, addition of cellulase and inoculants can decrease the concentrations of butyric acid and ammonia-N at different extents compared with control. Usually, low digestive rate is one of the important factors of restriction wheat straw as livestock feed. This test using fresh straw as material, treated by lactobacillus and cellulase in the process of silage fermentation, not only improve the fermented quality, but promote the digestibility of wheat straw can be expected. The evaluating of the LAB and cellulase treated wheat straw silage through livestock digest test evaluation will be carried out in our laboratory.

LAB inoculation, especially the addition together with cellulase, could improve the fermentation quality of wheat straw silage better than only cellulase-treated silages. L. casei Z3-1 has a potential ability to be used as commercial inoculant, and its effectiveness on other crop silages are underway in our laboratory.

This work was supported by Foundation of Henan Science and Technology Committee (Grant No. 132300410054, We thank Snow Brand Seed Co. Ltd. (Sapporo, Japan) for providing the commercial LAB inoculant.