Study On The Fermentation Quality,Aerobic Stability And In Vitro Ruminal Fermentation Characteristics Of Sweet Sorghum-alfalfa Silages

There are favorable natural advantages of developing herbivorous animal huabandry in Southern China,which can effectively solve the contradiction of human food versus animal feed competition,and promote agricultural structure regulation.Ruminant animal production such as cattle and sheep,the main driving force of development of herbivorous animal husbandry,is required to be supplied with year-around high quality forages.Sweet sorghum(Sorghum bicolor(L.)Moench;SS)belongs to C4 plant with high sugar contents and low crude protein contents,which collectively characterizes it to be ensiled well.Alfalfa(Medicago sativa L.;AF)belongs to legume with high nutritive value,is rich in crude protein,however,it is difficult to ensile due to low water soluble carbohydrates contents and high buffering capacity.High qulaity silages can be produced with ensiling SS and AF in certain proportions,which would meet the requirement of year-around high quality forages for ruminant animal production.Therefore,the first objective of this study was to evaluate the effect of ensiling SS with AF in different ratios on the fermentation quality,aerobic stability and in vitro ruminal fermenatation characteristics of silages,and then to select a best mixing ratio for SS-AF silage production.On the basis of the best mixing ratio of SS and AF for SS-AF silage production,the second objective was to determine if the addition of homofermentative/heterfermentative lactic acid bacteria mixtures and fibrolytic enzymes would enhance the fermentation quality,aerobic stability and in vitro ruminal fermenatation characteristics of SS-AF silages.The data obtained in this study can supply theoretical basis for the practical production of SS-AF silages in Southern China.This study consisted of the following six experiments:Experiment 1.The effect of different mixing ratios of sweet sorghum to alfalfa on the fermentation quality and ruminal nutrient degradability of silagesThe objective of this experiment was to determine the effect of different mixing ratios of SS to AF on the fermentation quality and ruminal nutrient degradability of silages.Five experimental treatments varying in the ratio of SS to AF:100:0(SAO),75:25(SA25),50:50(SA50),25:75(SA75)and 0:100(SA100)on a fresh matter basis were prepared.All experimental treatments were ensiled for 45 d in laboratory silos(six silo replicates per treatment),after which silage samples were taken to evaluate the fermeantation quality with measuring the chemical and nutritive composition.Further,the experimental silages were subjected to an in situ nylon bag experiment to evaluate the kinetics of ruminal degradability of dry matter(DM),crude protein(CP),neutral detergent fiber(NDF)and acid detergent fiber(ADF).The results showed that the heterofermentation enhanced with increasing proportion of AF in the SS-AF silages,as indicated by the fact that DM recovery,lactic acid contents and lactic acid to acetic acid ratios linearly decreased(P<0.05),while pH and acetic acid contents,linearly increased(P<0.05).Moreover,increasing proportion of AF in the SS-AF silages also enhanced clostridial fermentation,as indicated by the fact that butyric acid and ammonia nitrogen(NH3-N)contents as well as clostriadia spore counts linearly decreased(P<0.05).The CP contents linearly increased(P<0.05)with increasing proportion of AF in the silages,however,compared to the pre-ensiled forages of each treatment group,the CP loss was higher in SA50,SA75 and SA100 silages than SA0 and SA25 silages.The effective degradability(ED)of DM and CP linearly increased(P<0.05)with increasing proportion of AF in the silages,while the ED of NDF and ADF linearly decreased(P<0.05).The results obtained in this experiment indicated that the ratio of SS to AF of 75:25 was the most suitable for silage production considering the fermentation quality and nutritive value of mixed silages.Experiment 2.The effect of different mixing ratios of sweet sorghum to alfalfa on the aerobic stability of silagesThe objective of this experiment was to determine the effect of different mixing ratios of SS to AF on the aerobic stability of silages.Five experimental treatments varying in the ratio of SS to AF:SA0,SA25,SA50,SA75 and SA100 on a fresh matter basis were prepared.All experimental treatments were ensiled for 45 d in laboratory silos(six silo replicates per treatment),after which silage samples were collected and mixed homogeneously,and placed into a polyethylene plastic bottle(2 L capacity)to detecte the aerobic stability of silage,and then to evaluate the changes of the pH value,NH3-N content,and lactic acid bacteria,yeast,mould and clostridia spore counts of air-exposed silages at the 0th,3th,5th and 7th d.In addition,the chemical composition of air-exposed silages at the 7th d was also analysed.The results showed that the aerobic stability linearly increased(P<0.05)with the increasing proportion of AF in the silages.The aerobic stability of SAO,SA25,SA50,SA75 and SA100 silage was 69.7,80.0,99.5,>168 and>168 h,respectively.The pH value,NH3-N content,and lactic acid bacteria,yeast,mould and clostridia spore counts of all silages gradually increased(P<0.05)with the time of air exposure,and these parameters increased more rapidly in SA0,SA25 and SA50 silages than SA75 and SA100 silages.Compared to the silages with different treatments at 45 d,the DM,water soluble carbohydrates and CP contents of the air-exposed silages with different treatments at 7th d decreased,while other chemical compositions increased.The results obtained in this experiment indicated that increasing proportion of AF in the SS-AF silages is benefit of improving the aerobic stability of mixed silages,and inhibiting the growth of yeasts,moulds and clostridia spores?Experiment 3.The effect of different mixing ratios of sweet sorghum to alfalfa on the in vitro ruminal fermentation characteristics of silagesThe objective of this study was to determine the effect of different mixing ratios of SS to AF on the in vitro ruminal fermentation characteristics of silages.Five experimental treatments varying in the ratio of SS to AF:SA0,SA25,SA50,SA75 and SA100 on a fresh matter basis were prepared.All experimental treatments were ensiled for 45 d in laboratory silos(six silo replicates per treatment).The gas production,methane production,nutrient degradability,microbial enzyme activity,fermentation parameters,microbial protein(MCP)concentration and relative populations of cellulolytic and proteolytic bacteria of the five experimental silages after 48 h in vitro fermentation were determined with the in vitro gas technique.The result showed the gas production,in vitro NDF degradability(IVNDFD),activity of carboxymethyl cellulose,cellobiase and xylanase,short-chain fatty acids(SCFA),propionic acid molar proportion,MCP concentration,relative quantity of Fibrobacter succinogenes and Ruminococcus flavefaciens linearly increased and then decrease(P<0.05)with increasing proportion of AF in the SS-AF silages after in vitro inoculation for 48 h;the methane production,NH3-N concentration,acetic acid molar proportion and ratio of acetic acid to propionic acid linearly decreased and then increased(P<0.05);the in vitro DM degradability(IVDMD),in vitro CP degradability(IVCPD),activity of protease,pH,molar proportion of isovaleric acid,valeric acid and isobutyric acid,relative quantity of genus Prevotella linearly increased(P<0.05);the in vitro ADF degradability(IVADFD),activity of ?-amylase,butyric acid molar proportion,relative quantity of Butyrivibrio fibrisolvens and Ruminobacter amylophilus linearly decreased(P<0.05).Compared to other silages,SA25 treatment had the highest the gas production after in vitro inoculation for 48 h,IVNDFD,activity of carboxymethyl cellulose,cellobiase and xylanase,SCFA and MCP concentrations,and relative quantity of Fibrobacter succinogenes and Ruminococcus flavefaciens,and the lowest ratio of acetic acid to propionic acid and methane production.The results obtained in this experiment indictaed that SA25 silage is a relative energy and nitrogen balance,under the same conditions of usage,there could be benefits for increasing MCP synthesis and reducing excretion to the environment,and facilitating the use of energy and nitrogen by ruminat animals with SA25 silage rather than other silages.Experiment 4.The effect of additives on the fermentation quality and ruminal nutrient degradability of sweet sorghum-alfalfa silagesThe objective of this experiment was to determine the effect of additives on the quality and ruminal nutrient degradability of SS-AF silages.The mixture of 75%SS+25%AF was chose as the ensiling material.Four experimental treatments were prepared:(1)no additives(Control);(2)lactic acid bacteria(LAB);(3)fibrolytic enzymes(E);(4)lactic acid bacteria+fibrolytic enzymes(LE).All experimental treatments were ensiled for 45 d in laboratory silos(six silo replicates per treatment),after which silage samples were taken to evaluate the fermeantation quality with measuring the chemical and nutritive composition.Further,the experimental silages were subjected to an in situ nylon bag experiment to evaluate kinetics of ruminal degradability of DM,CP,NDF and ADF.The results showed that LAB and E addition improved the fermentation quality of SS-AF silages,as indicated by higher(P<0.05)DM recovery and lactic acid contents,lower(P<0.05)pH values and NH3-N contents,however,LAB and LE silages had higher acetic acid contents than the Control silage.LAB and E addition had significant effects on increasing the true protein contents,and decreasing non-protein nitrogen and soluble protein contents.E and IE addition decreased(P<0.05)the NDF and ADF contents,while increased(P<0.05)water soluble carbohydrates contents.LAB and E showed a supplemental effect on the fermentation quality of SS-AF silages,and LE addition further increased the DM recovery and lactic acid content of SS-AF silages,and decreased the pH and NH3-N content.Compared to the Control,LAB,E and LE addition improved(P<0.05)the ED of DM and CP,while had no effects(P>0.05)on the ED of NDF and ADF.The results indicated that LE addition at ensiling can to the greatest extent reduce proteolysis and improve fermentation quality of SS-AF silages,thus,achieving the best quality silage.Experiment 5.The effect of additives on the aerobic stability of sweet sorghum-alfalfa silagesThe objective of this experiment was to determine the effect of additives on the aerobic stability of SS-AF silages.The mixture of 75%SS+25%AF was chose as the ensiling material.Four experimental treatments were prepared:(1)Control;(2)LAB;(3)E;(4)LE.All experimental treatments were ensiled for 45 d in laboratory silos(six silo replicates per treatment),after which silage samples were collected and mixed homogeneously,and placed into a polyethylene plastic bottle(2 L capacity)to detect the aerobic stability of the silages,and then to evaluate the changes of the pH value,NH3-N content,and lactic acid bacteria,yeast,mould and clostridia spore counts of air-exposed silages at the 0th,3th,5th and 7th d.In addition,the chemical composition of air-exposed silages at the 7th d was also analysed.The results showed that additives had a significant effect(P<0.05)on the aerobic stability of SS-AF silages.The aerobic stability of the Control,LAB,E and LE silages was 80.0,70.0,91.2 and 90.3 h,respectively.Compared to the Control,E addition accelerated the elevation of the pH value,NH3-N content,and yeast,mould and clostridia counts of SS-AF silages during air exposure,while LAB addition slowered the elevation of the pH value,NH3-N content,and yeast,mould and clostridia spore counts during air exposure.the non-protein nitrogen and soluble protein contents of air-exposed silages at 7th d were higher(P<0.05)in LAB and LE silages than the Control silage,while were lower(P<0.05)in E silage.The results obtained in this experiment indicated that LAB addition improved the aerobic stability of SS-AF silages and decreased the extent of proteolysis,while E addition decreased the aerobic stability and increased the extent of proteolysis.Experiment 6.The effect of additives on the in vitro ruminal fermentation characteristics of sweet sorghum-alfalfa silagesThe objective of this study was to determine the effect of additives on the in vitro ruminal fermentation characteristics of SS-AF silages.The mixture of 75%SS+25%AF was chose as the ensiling material.Four experimental treatments were prepared:(1)Control;(2)LAB;(3)E;(4)LE.All experimental treatments were ensiled for 45 d in laboratory silos(six silo replicates per treatment).The gas production,methane production,nutrient digradability,microbial enzyme activity,fermentation parameters,MCP concentration and relative populations of proteolytic and fibrolytic bacteria of the four experimental silages after 48 h fermentation were evaluated with the in vitro gas technique.The results showed that LAB and E addition had significant effects on the rumen fermentation.Compared to the Control,LAB,E and LE addition improved(P<0.05)the IVDMD and IVCPD,protease activity,MCP concentrations and relative populations of genus Prevotella,and decreased(P<0.05)the ratio of acetic acid to propionic acid and methane production,and LE silage had the highest IVDMD and IVCPD,protease activity and MCP concentration,and the lowest ratio of acetic acid to propionic acid and methane production.These results obtained in this experiment indicated that the additives addition can improve the efficiency of rumen fermentation of SS-AF silages,which was related to their effects on stimulating the growth of genus Prevotella in the rumen,and LE addition was the most effective on increasing MCP synthesis and decreasing methane production.In conclusion,the results of the experiments indicated that the ratio of SS to AF of 75:25 was the most suitable for silage production due to the optimal balance of fermentation quality,aerobic stabilty and in vitro ruminal fermentation characteristics;the results of the experiments indicated that the addition of combination of lactic acid bacteria and fibrolytic enzymes was the most effective on improving the fermentation quality,aerobic stability and in vitro ruminal fermentation characteristics of SS-AF silages.