Yield, composition and in vitro digestibility of new forage sorghum varieties and their ensilage characteristics

The objective of this study was to examine the effect of the ensilage process on yield, composition and in vitro digestibility of three new forage sorghum (Sorghum bicolor) varieties: Silobuster, Supersile 20, and the brown-midrib hybrid BMR-101. The commercial forage sorghum FS-5 was used as reference variety. Varieties were irrigated during summer with 242 mm water and harvested at their soft dough (SD) stage. All varieties were tall (>2.5 m), and their dry matter (DM) content at harvest was similar (270-280 g DM/kg green forage). FS-5 and BMR-101 contained higher proportion of heads on the account of lower proportion of leaves in FS-5, and stems in BMR-101. In all varieties the leaves tended to contain more neutral detergent fiber (aNDFom) and were characterized by lower DM digestibility as compared with the stems and heads organs. Silobuster and BMR-101 suffered from high lodging (43-65%), whereas FS-5 and Supersile 20 were characterized by moderated levels of lodging (27-30%) at harvest. Dry matter yield of the green forage was similar (15.3-16.5 t/ha) in all varieties. The ensilage of all varieties in glass silos resulted in moderated DM losses (<0.09 of yield) mostly as volatile gases, solubilization of 0.05-0.15 hemicellulose, and high conversion of water soluble carbohydrate (WSC) mostly into lactate, traces of ethanol and traces of volatile fatty acids (VFA). Consequently, similar pH (<4) was obtained in the silages of all varieties. In vitro DM digestibility of silage was similar in all varieties and ranged between 0.67 and 0.69. Silage aNDFom digestibility and yields per hectare of digestible silage DM and aNDFom were also similar. Ensilage resulted in 0.09-0.15 loss of digestible DM yield per hectare, and 0.04-0.14 loss of digestible aNDFom yield per hectare. Efficiency of water utilization for the production of digestible silage DM was high in all varieties. This study shows advantage of commercial FS-5 over the new varieties due to its better resistance to lodging and high quality silage.