Attempt to practically use a lactic acid bacterial strain, SP 1-3, for making good quality silage in Thailand

Feeding of good quality silage (GQS) throughout the year is a suitable way to stably increase raw milk production in spite of its not being in wide use in Thailand. However, making GQS in Thailand is not always ensured if ensilage depends on natural fermentation. Therefore, lactic acid bacteria (LAB) strains to make GQS were screened, and strain SP 1-3 was selected. 　　For the practical use of this strain, a culture method for harvesting large numbers of LAB cells in a low-cost and convenient way was examined, and a culture medium composed of materials that are readily available in Thailand was designed. The medium designed here consisted of molasses 2.0%, rice bran 0.5%, yeast extract 0.2%, and mineral mixture (pH 6.5), and gave a cell mass of 109 cfu/ml after 24 h culture at 35˚C. The cost of this medium was calculated at about 23 yen/L, about 1/60 of that of MRS broth. A silage inoculant (spray-dried granule) from strain SP 1-3 cultured using this medium was prepared for trial. This granule was stable and kept a living cell count of 108~9 cfu/g under storage at 4˚C for 28 days, as shown in Table 1, and reliably improved the fermentation quality of Napier grass silage prepared beforehand in the laboratory. To use these granules for the preparation of practical-scale silage, a low-cost and convenient method of increasing the cell mass of the LAB strain at farm level was developed using a 5-liter plastic drinking water bottle. LAB cell counts in the water (4.5 L), in which had been suspended 45 mg of granules together with the abovementioned medium, rose to 3.85 x 109 cfu/ml after culturing for 24 h. This LAB liquid (4.5 L) is ideal for preparing 4.5 ton of GQS. The additional cost using this system was calculated to be about 50 yen/ton. 　　Based on these results, Pangola grass and Erianthus silages inoculated with the LAB liquid were prepared on a practical scale. After being kept at 30~35˚C for 90 days, the silage pH, the organic acids and volatile basic nitrogen (VBN) content and microbial cell counts were examined. The results are shown in Table 2. Compared with silage without inoculation of LAB, the fermentation quality of silage inoculated with LAB liquid was improved as shown as pH reduced to below 4, increased lactic acid content, and reduced VBN content. These improvements were particularly notable in Erianthus silage. However, the yeast cell count was not reduced by inoculation with LAB. Abundant yeast cells in silage prepared in Thailand were hitherto known, and this trend was marked in the case of Pangola grass silage in this experiment. Abundant yeast cells in silage leads to the outbreak of aerobic deterioration after opening the silo. However, silage pH 48 h after opening the silo rose to almost neutral while the pH was about 3.5 on initial opening. 　　In addition, the palatability of silage inoculated with LAB was compared with non-inoculated silage by the cafeteria method using Brahman steers and native Thai steers. However, no significant difference in intake amount was seen between both types of silage (data not shown). (S. Ohmomo)

Table 1.  Variation in the survival of the cells in granules prepared from strain SP 1-3. Table 2.  Fermentation quality of practical-use silage inoculated with LAB strain SP 1-3.

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