Effects Of Additives On Aerobic Stability Of Silage Corn And Its Mechanis

The aerobic stability of silage has an important impact on the quality utilization and livestock production efficiency,and the use of additives can effectively prolong the aerobic stability of silage.In this study,the following treatments were used for silage after inoculation of whole maize with indigenous screened Lactobacillus rhamnosus and Lactobacillus buchneri and acetic acid: CK(control);LR(inoculated with Lactobacillus rhamnosus);LB(inoculation with Lactobacillus buchneri);M(combined inoculation with Lactobacillus rhamnosus and Lactobacillus buchneri)and YS(inoculation with acetic acid).Microbial communities and metabolomes were studied in fresh samples,silage for 60 d and after 180 d of aerobic exposure for 0,2,5and 9 d.The main findings were as follows:(1)Lactic acid bacteria(LAB)and YS inoculation treatments improved the fermentation quality of silage.The water soluble carbohydrates(WSC)and crude protein(CP)contents of silage 180 d were significantly lower than 60 d(P<0.05),but the fermentation quality was higher than 60 d.The number of LAB,yeast and coliform in the 180 d group was significantly lower than that of silage 60 d(P<0.05).The nutritional quality,fermentation quality and aerobic stability of LB and LR were better than CK,YS and M after 60 d of silage and 9 d of aerobic exposure.In the180 d group of silage,the nutritional quality and fermentation quality of LB and LR were better than CK,YS and M,but there was no difference in aerobic stability.(2)After 60 d of silage,the duration of aerobic stabilization was 41 h,55.5 h and106 h for the CK,YS and M treatments,respectively,and the LB and LR groups remained free of spoilage after 9 d of aerobic exposure;after 180 d of silage,no spoilage occurred in all treatments after 9 d of aerobic exposure.(3)The dominant bacterial phyla before and after silage and during aerobic exposure were Proteobacteria and Firmicutes.Weissella were absolutely dominant before silage.After 60 d of silage,Acetobacter and Lactobacillus were the dominant genera,and the relative abundance of Acetobacter increased rapidly over Lactobacillus as aerobic exposure progressed.After 180 d of silage,the dominant genera were Acetobacter,Lactobacillus and Ralstonia.(4)Silage time and inoculation treatments significantly altered metabolite composition and metabolic pathways.the LR group improved aerobic stability by affecting the metabolic pathway of benzoxazine biosynthesis,obtaining higher relative abundance of indoles to promote synthesis of benzoxazinoids,and inhibiting fungal growth.The mixed addition of the two LAB produced an antagonistic effect,resulting in weaker synthesis of both acetic acid-producing and benzoxazinoids than the LAB addition alone,ultimately manifesting as improved aerobic stability but lower than that of LB and LR.the differential metabolic pathways of LR and LB were caprolactam degradation and tryptophan metabolism.The improvement of aerobic stability of maize silage after acetic acid treatment was associated with bisphenol degradation.(5)Acetic acid addition inhibited the synthesis of organic acids such as L-methionine and L-phenylalanine and their derivatives as well as lipids and lipid-like molecules,and promoted the synthesis of nitrogenous organic compounds such as isoferulic acid and betaine as well as organic heterocyclic compounds.Most of the metabolite changes after mixed addition of homo-and heterotypic LAB were similar to the results of single addition of LAB,but inhibited the synthesis of antecedent metabolites,such as indole,that favor the production of amino acids.In summary,inoculation of both LAB strains increased acetate production decreased p H,both promoted the growth of Lactobacillus and altered microbial communities and metabolic pathways in different ways.Although the mixed addition of both LAB prolonged the aerobic stability of the silage,the effect was not as prominent as the single addition of LAB.Acetic acid addition had a positive effect in terms of improving aerobic stability,although it was detrimental to the growth of LAB.