| Corn stover has great potential utility as a ruminant feed because it contains large proportions of cellulose and hemicellulose.However,the use of corn stover as roughage is limited because its ruminal digestibility is poor.The traditional chemical methods of pretreating corn stover,such as with ammonia,urea,or calcium hydroxide,entail problems of low efficiency and potential environmental pollution.Steam explosion is an efficient pretreatment that changes the physical and chemical character of the lignocellulosic biomass,and is used in bioenergy industries.However,there is limited information about the steam explosion of corn stover to increase its ruminal fermentation.The purpose of this study was to characterize the morphological structure,rumen fermentation and microbial colonization of steam-exploded corn stover.1.Optimization of steam explosion of corn stover for animal feedThe steam explosion of corn stover was evaluated by the response surface methodology(RSM)based on the Box-Behnken design.The optimal operation parameters including steam pressure(1.0,1.6,or 2.2 MPa),processing time(30,115,or 200 s)and water content(10%,30%,or 50%)were identified,taking greater gas production rate during rumen fermentation in vitro as the desired outcome,and different treats analyzed with NIR.The software Design-Expert was used for optimum levels statistics.The results were as follows:(1)ANOVA analysis indicated that the quadratic term of pressure played a dominant role(P<0.01)in the steam explosion pretreatment.(2)The optimal condition predicted at 1.51 MPa,with maintaining time of 180 s and 10%water,which led to the highest c of 0.082 mL/h for steam exploded corn stover.(3)The NIR pattern did not change between the different samples,and NIR absorbance of corn stover increased after steam explosion.2.Effect of steam explosion on in vitro gas production and morphological structure of corn stoverTo investigate the effect of steam explosion on in vitro gas production of corn stover,in vitro cultivation was conducted for 72 h with the rumen fluid collected from three dairy cows.Accumulative gas production in 72 h,fermentation kinetic parameters were determined after the 72 h incubation.The chemical components and morphological structure of steam-exploded corn stover were analyzed.The results were as follows:(1)Steam explosion significantly reduced the content of NDF and hemicellulose in the corn stover(P<0.01),and increased the production of total reducing sugars(P<0.01)and xylose(P<0.05),significantly.(2)Compared with raw corn stover,steam explosion increased rate of gas production significantly(P<0.01)but have little effect on GP72h(P>0.05).(3)Scanning electron microscopy(SEM)showed that the steam-exploded corn stover became more disordered and looser,suggesting that it is more accessible to rumen microbes.Fourier transform infrared spectroscopy(FTIR)indicated that the weakened of hemicellulose characteristic peak and the enhanced of cellulose characteristic peak after steam explosion.X-ray diffraction showed the crystallinity of raw and steam exploded corn stover were 54.50%and 57.57%respectively(P>0.05).An increase in the crystallinity of the corn stover after steam explosion,indicated the removal of hemicellulose and amorphous cellulose.3.Effect of steam explosion on In-sacco fermentation and bacteria colonizationThe in sacco incubation of raw and steam-exploded corn stover was assessed with nylon bags in the rumen of four dairy cows,in which raw and steam-exploded corn stover was incubated for 0.5,1,2,4,8,12,24,36,and 48 h,analyzed for degradation,and examined with SEM to observe the microbes present.The results were as follows:(1)In this study,the NDF degradation of steam-exploded corn stover at 4.24,36 and 48 h incubation reached 3.92%.28.85%,37.73%and 45.80%respectively,which were significantly higher than those of raw corn stover(P<0.05).The hemicellulose degradation of steam-exploded corn stover at 4,24.36 and 48 h incubation reached 6.57%,33.74%,40.63%and 49.00%respectively,which were significantly higher than those of raw corn stover(P<0.01).Furthermore,the ADF degradation of steam exploded corn stover at 48 h incubation reached 44.83%,significant higher than that of raw corn stover(P<0.01),The cellulose degradation of steam exploded corn stover at 48 h incubation reached 47.57%,significant higher than that of raw corn stover(P<0.05).(2)SEM showed that bacterial colonization in steam-exploded corn stover grew faster than raw corn stover,In conclusion,steam explosion facilitates the attachment of microbes to corn stover and its degradation in the rumens of dairy cows. |
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