عنوان مقاله [English]
Introduction: Corn silage is a major source of forage for ruminants, which provides a higher energy level compared to other forages. But it is susceptible to aerobic deterioration, because yeasts utilise the lactic acid, produced by lactic acid bacteria, as a source of energy. Thus, silages become a favour environment for the growth of mold and bacteria. The susceptibility of a silage to the aerobic deterioration is an important factor since it is directly related to its quality and nutritive value. When silage is exposed to air, increase of temperature and pH may occur, resulting in soluble carbohydrates loss and fermentation of the products of microbial metabolism, reducing its quality. Aerobic stability is an important feature in the evaluation of corn silage quality. Researchers reports that the use of lactic acid bacteria can improve fermentation and aerobic stability of silage. This study aimed to investigate the changes in the chemical compositions and concentration of fermentation end products that occur in corn silages with or without microbial inoculants during aerobic exposure and to select bacterial strains that can improve the aerobic stability after silo opening.
Materials and methods: this assay was conducted to select lactic acid bacteria (LAB) strains isolated from corn silage, the intestinal contents of broilers, laying hens, Turkey, Ostrich and assess their effects on the quality and aerobic stability of maize silage. The LAB strains were inoculated into aqueous extract obtained from maize to evaluate their production of metabolites, pH reduction and antimicrobial activity. One hundred and twenty-one strains were isolated from various sources in the Laboratory, which all isolates were considered to be LAB as determined by Gram-stain appearance, catalase test and lactic acid productivity. Analysis of the 16S rDNA sequence of representative strains was used to confirm the presence of the predominant groups. The sequences from the various LAB isolates showed high degrees of similarity to those of the GenBank type strains between 99% and 100%. Five LAB strains that showed the best results were assessed in experimental silos. All treatments were ensiled in laboratory-scale silos for 105 days, and then subjected to an aerobic stability test for 8 days. Silage samples were collected at 0, 4 and 8 days after aerobic exposure to determinate the changes in the chemical compositions, products of fermentation, and to evaluate the silages microbial changes to determine the aerobic deterioration. Data in the experimental design, after opening the silos, were analysed in a completely randomized design with nine replicates by GLM procedure of SAS software. In aerobic conditions, the data were analyzed as repeated measures in time. The data were analysed in a completely randomized design by GLM procedure of SAS software. Variance analysis and multiple comparisons of data were performed using the GLM procedure of and the means were separated by Tukey’s test.
Results and Discussion: The results indicated that after 105 days of conservation, all silages had good fermentation characteristics with low pH (<3.80) and ethanol concentration and high lactic acid contents (P<0.01). A linear decrease in pH values and water soluble carbohydrates contents were observed. Addition of lactic acid bacteria, increased acetic acid, but decreased ethanol contents of inoculated silages compared to the control (P<0.01). Across treatments, there were significant differences in the yeast populations (P<0.01). The population of yeasts which was initially high in the fresh forage (5.57 log cfu g−1 forage) before ensiling and a drastic reduction in the numbers of yeasts was observed in all silages throughout the experiment. The addition Lactobacillus Fermentum resulted in a higher concentration of acetic acid and reduced populations of yeasts in silage compared to the other silage treatments, and a lower ethanol concentration in the silage (P<0.01). The strains tested were able to modify the fermentative and chemical parameters and the populations of yeasts of silage after aerobic exposure. Aerobic stability of corn silages was associated with high acetic acid and reduction the populations of yeasts. all Lactobacillus strains promoted an increase in aerobic stability of silage. Addition of lactic acid bacteria, further improved silage aerobic stability with more acetic acid production and reduction the populations of yeasts (P<0.01). After 8 days of aerobic exposure, inoculated silage with Lactobacillus Fermentum remained stable, but the control silage deteriorated as indicated by a reduction in lactic acid and an increase in pH, and numbers of yeast (P<0.01). These results proved the advantage of microbial inoculation. The best Lactobacillus strains is Lactobacillus Fermentum because it provides more stable pH, production higher acetic acid, higher reduction of yeasts and filamentous fungi in maize silage, thereby decreasing the aerobic deterioration by these microorganisms.
Conclusion: The results showed that the use of inoculants is recommended because it promoted higher production of acetic acid, reducing the populations of yeast and filamentous fungi, a more stable pH and, therefore, improving the aerobic stability of silages.
The best inoculation is Lactobacillus Fermentum because it provides higher reduction of yeast and filamentous fungi in maize silage, thereby decreasing the aerobic deterioration by these microorganisms. the Lactobacillus Fermentum strain show the best results in relation to silage aerobic stability.