Use of biological additives to improve lactic fermentation tropical silages

Abstract Text: The objective of this study was to assess different biological additives to favor lactic acid fermentation. This trial aimed also to obtain the optimal proportions of sorghum/soybean to ensure good fermentation quality for silage making using a fast in vitro fermentation test (Rostock fermentation test (RFT). Different combinates of a grass (Sorghum bicolor L. variety H70) and legume (soybean Glycine max variety Panorama 29) were tested against biological additives. Test used sorghum and soybean and their combinations (100/0, 33/67, 67/33, 0/100) with or without biological additives. Inoculates were evaluated for their acidification ability: enzymatic complex from anaerobic rumen fungi (Orpinomyces sp), clarified rumen fluid, Lactic acid bacteria (LAB)-epiphytic S738 (from sorghum), LAB-epiphytic S739 (from soybean), LAB from CIAT bacteria collection (S66.7), commercial silage inoculant (SilAll4×4-Brazil) and a control. Fifty grams of fresh minced material and 200ml of distilled water of forage were incubated into sterile glass in triplicate at 37°C for 48 hours and the pH was measured at 0,20,28,44 and 48 hours to determine the dynamics of fermentation. Completely randomized in a 4x6 factorial design was used. Forage inclusion level (four levels) and the type of additive (six additives and control) were arranged. Significant difference (P<0.001) was found at the level of forage inclusion and the additive used (P<0.05). The treatments including biological additives showed lower pH value than control treatment (5.5). Best results were obtained (pH=3.7) for the sorghum/soybean at 100/0% inclusion, followed by the mixture of sorghum/soybean 67/33 (pH=4.2) while the pH for the rest of treatments value were above 5.0. The best additive was the bacterial strain (S738) (pH <4.0). The enzymatic complex (pH 5.0), clarified rumen fluid  (pH 5.3) and silall4x4 (pH 5.2) have reasonable pH values for ensilability. The highest pH value (5.7) was for soybean 100% (P<0.05). Results show that biological additives such as epiphytic bacterial strains isolated from sorghum have potential to improve fermentability. Larger sorghum inclusion in the mixture facilitated lactic fermentation for silage making.

Keywords: pH, Rostock Fermentation Test RFT, grass, legume.