Field yield, ensiling properties and digestibility by sheep of silages from two forage sorghum varieties

This study examines the yield, composition, digestibility and ensiling properties of the new sorghum brown-midrib hybrid BMR-101. The commercial forage sorghum FS-5 was used as a reference variety. Forages were grown in a typical Mediterranean climate in five replicate plots, irrigated with 250 mm water, combine harvested at the soft dough stage and ensiled under both laboratory and commercial conditions. Both varieties were tall (> 2.0 m). The dry matter (DM) content at harvest of FS-5 was higher than that of BMR-101 (296 g/kg forage versus 255 g/kg forage, P < 0.05). BMR-101 plants suffered from higher lodging than FS-5 plants (60% versus 16.7%, P < 0.05). Dry matter (DM) yield of the green forage was higher for FS-5 than BMR-101 (12.1 t/ha versus 9.89 t/ha, P < 0.05). The distribution of DM among plant organs was similar for the two varieties, which contained also similar levels of neutral detergent fiber (aNDFom, 560-563 g/kgDM). BMR-101 raw plants had higher content of crude protein (CP) and hemicellulose and lower content of water-soluble carbohydrate (WSC), cellulose and lignin than FS-5 plants. Ensiling of the two varieties in glass silos resulted in moderate DM losses (< 0.08 of yield) mostly as volatile gases, solubilisation of 0.04-0.12 hemicellulose, and high conversion of WSC mostly into lactate, ethanol and acetate. Ensiling in large scale bunker silos resulted in more extensive fermentation of WSC and lactate into acetate and ethanol, but in similar low pH (< 4). In vitro DM digestibility of the two silages was similar, but in vitro NDF digestibility was higher for BMR-101 silage than FS-5 silage (P < 0.05). Eight Assaff rams were assigned randomly into two dietary groups of four rams each and fed the two silages in a 2 x 2 crossover design. Intake and digestibility by sheep of silage DM and CP were similar for both varieties. Digestibility of silage NDF, cellulose and hemicellulose was higher for sheep fed BMR-101 as compared with FS-5 (P < 0.05). The production of digestible silage DM was calculated to be higher for FS-5 than BMR-101 (7.14 t/ha versus 6.13 t/ha, P < 0.05). These data highlight the advantages of commercial FS-5 relative to the new BMR-101 variety: its better resistance to lodging and higher production of silage DM and digestible DM per ha. (c) 2006 Elsevier B.V All rights reserved.