Ensilability and Nutritive Value of Sweet Sorghum and Sweet Pearl Millet Bagasse as Affected by Different Methods of Carbohydrate Extraction for Eventual Ethanol Production

HighlightsJuice extraction resulted in a decrease in the nutritive value of the bagasse as compared with the initial biomass.Silages made from the second pressing bagasse were well conserved.Sweet sorghum silage has a better nutritive value than sweet pearl millet.Abstract. Pressing the biomass of sweet sorghum and sweet pearl millet in-field is one of the suggested options for bioethanol production. The extracted juice can be delivered to an ethanol plant, and the bagasse (pressing residue) can be used for ruminant feeding. Efficient carbohydrate extraction is highly important for good ethanol yield. However, enough carbohydrates must remain in the bagasse for its adequate conservation as silage. In this study, the ensilability and the chemical composition of the second pressing bagasse of sweet sorghum and sweet pearl millet were investigated. The bagasse was obtained following a second pressing of the first pressing bagasse after its impregnation with water based on three water:bagasse ratios (0.5, 1, and 1.5). Results indicated that water:bagasse ratio did not affect water-soluble carbohydrate (WSC) extraction for both crops. The second pressing bagasse of sweet sorghum and sweet pearl millet contained 80.5 ±4.6 and 60 ±4.6 g of WSC kg-1 dry matter (DM), respectively. The second pressing bagasse of both crops had reduced nutritive value compared to the initial biomass, i.e., higher neutral detergent fiber (NDF) and acid detergent fiber (ADF) concentrations along with lower non-structural carbohydrate (NSC) concentration, in vitro true digestibility of DM (IVTD), and in vitro NDF digestibility (NDFd). The second pressing bagasses of both crops also showed good ensilability, but sweet sorghum bagasse silages were of better nutritive value than sweet pearl millet bagasse silages (ADF = 446.2 ±3.7 vs. 463.2 ±3.7 g kg-1 DM, IVTD = 813.8 ±3.4 vs. 708.8 ±6.8 g kg-1 DM, and NDFd = 741.8 ±4.8 vs. 596.2 ±8.5 g kg-1 NDF, respectively). The water:bagasse ratio used for bagasse impregnation before the second pressing only affected the NDF concentration of silages, as a higher NDF concentration was obtained with a water:bagasse ratio of 1.5. Sweet sorghum and sweet pearl millet can be considered dual-purpose crops; the extracted juice can be fermented into ethanol, and the second pressing bagasse can be used to make good-quality silage. Keywords: Bagasse impregnation, Nutritive value, Silage, Sweet pearl millet, Sweet sorghum, Water-soluble carbohydrates.