Aims: Acetic acid is considered an important preservative in tropical grass ensiling. The objective of the current experiments was to follow the ensiling fermentation of low dry matter (DM) tropical grass as a model to study changes in bacterial communities during acetic acid fermentation. Methods and Results: Direct‐cut and wilted guinea grass silage was prepared with and without molasses. A high acetic acid level was observed during the fermentation of direct‐cut silage, and long storage increased the butyric acid and ethanol content if molasses was not added. The lactic acid production in wilted silage was greater than the acetic acid production, but prolonged ensiling decreased the lactic to acetic acid ratio regardless of molasses addition. Adding molasses enhanced the lactic acid content in both direct‐cut and wilted silage. The bacterial community, identified by denaturing gradient gel electrophoresis, was affected by wilting and molasses addition. Bands for Pantoea sp. and Morganella sp. became faint when acetic acid fermentation was suppressed, and those for Pediococcus pentosaceus and Lactococcus garvieae were detected when lactic acid fermentation was enhanced by wilting and molasses addition. Lactobacillus plantarum and Lactococcus lactis were found throughout the ensiling process in all silage types. Conclusion: Distinct changes occurred in the bacterial community in guinea grass silage because of wilting and molasses addition. These changes could explain how lactic acid fermentation was enhanced but could not help determine which bacteria were associated with enhanced acetic acid fermentation. Significance and Impact of the Study: The study reveals the effects of wilting and molasses during ensiling of low DM tropical grasses and the associated bacteria.
Aims: To examine how storage temperatures influence ensiling fermentation, aerobic stability and microbial communities of total mixed ration (TMR) silage. Methods and Results: Laboratory-scale silos were stored at 5, 15, 25 and 35°C for 10, 30 and 90 days. If silage was stored at 5°C, fermentation was weak until day 30, but acceptable lactic acid production was observed on day 90. The ethanol content was higher than the acetic acid content when stored at 15 and 25°C, whereas the ethanol content was lower when stored at 35 than at 25°C. Aerobic deterioration did not occur when silage was exposed to air at the same temperature at which it was stored. Although 10-day silages stored at 5 and 15°C deteriorated when the aerobic stability test was conducted at 25°C, heating was not observed in silages stored at 25 or 35°C or in any 90-day silages regardless of storage temperature. Denaturing gradient gel electrophoresis demonstrated that bands indicative of Lactobacillus plantarum and Lactobacillus delbrueckii were less prominent, while bands indicative of Lactobacillus panis became more distinct in silages stored at high temperatures. Bands of Kluyveromyces marxianus were seen exclusively in silages that were spoiled at 25°C. Conclusion: High ambient temperature enhances acetic acid production in TMR silage. Lactobacillus panis may be associated with changes in the fermentation products due to differences in storage temperature. Significance and Impact of the Study: The role of Lacto. panis in ensiling fermentation and aerobic stability is worth examining.
Aims: To characterize the bacterial communities in commercial total mixed ration (TMR) silage, which is known to have a long bunk life after silo opening. Methods and Results: Samples were collected from four factories that produce TMR silage according to their own recipes. Three factories were sampled three times at 1‐month intervals during the summer to characterize the differences between factories; one factory was sampled 12 times, three samples each during the summer, autumn, winter and spring, to determine seasonal changes. Bacterial communities were determined by culture‐independent denaturing gradient gel electrophoresis. All silages contained lactic acid as the predominant acid, and the contents appeared stable regardless of factories and product seasons. Acetic acid and 1‐propanol contents were different between factories and indicated seasonal changes, with increases in warm seasons compared to cool seasons. Both differences and similarities existed among the bacterial communities from each factory and product season. Lactobacillus parabuchneri was found in the products from three of four factories. Various sourdough lactic acid bacteria (LAB) were identified in commercial TMR silage; Lactobacillus panis, Lactobacillus hammesii, Lactobacillus mindensis, Lactobacillus pontis, Lactobacillus frumenti and Lactobacillus farciminis were detected in many products. Moreover, changes owing to product season were distinctive, and Lact. pontis and Lact. frumenti became detectable in summer products. Conclusion: Sourdough LAB are involved in the ensiling of commercial TMR silage. Silage bacterial communities vary more by season than by factory. The LAB species Lact. parabuchneri was detected in the TMR silage but may not be essential to the product’s long bunk life after silo opening. Significance and Impact of the Study: Commercial TMR silage resembles sourdough with respect to bacterial communities and long shelf life. The roles of sourdough LAB in the ensiling process and aerobic stability are worth examining.
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