Effect of enzyme or microbial treatment of bermudagrass forages before ensiling on cell wall composition, end products of silage fermentation and in situ digestion kinetics

Abstract

Tifton 85 bermudagrass (T85) and Coastal bermudagrass (CBG) established on adjacent plots and managed similarly were harvested after 3 or 6 weeks of regrowth and used to investigate the effects of fibrolytic enzymes or microbial inoculant treatment before ensiling on nutrient composition and recovery, cell wall chemistry and digestion. Prior to ensiling T85 had higher concentrations of neutral detergent fiber (NDF) and acid detergent fiber (ADF), similar concentrations of total lignin, and greater ( p < 0.05) in vitro and in situ dry matter (DM) and NDF disappearances when compared with CBG. Coastal bermudgrass had higher ( p < 0.05) concentrations of acid-insoluble lignin and ether-linked ferulic acid (monomers and dimers), and lower concentrations of glucose and mannose than T85. Treatment of bermudagrass forages with microbial inoculant decreased ( p < 0.05) concentrations of NDF, hemicellulose, butyrate, lactate, cell walls and acid-insoluble lignin, and increased ( p < 0.05) concentrations of ammonia, total volatile fatty acids (VFA) and acetate in silages. Treatment of bermudagrass forages with fibrolytic enzymes had no effect on silage fiber concentration, cell wall carbohydrate fraction or concentration of p-coumaric and ferulic acids, but increased the concentration of butyrate. Among silages, T85 had higher ( p < 0.05) in vitro and in situ dry matter DM and NDF disappearance and higher ( p < 0.05) potentially digestible fractions and smaller ( p < 0.05) indigestible fractions of DM and NDF than CBG. Treatment of bermudagrass forages with fibrolytic enzymes had no effect on in vitro or in situ DM or NDF disappearance of silages. Treatment of bermudagrass forages with microbial inoculant increased in situ DM disappearance at 72 h of incubation ( p < 0.10) and the potentially digestible fraction of DM ( p < 0.05) of silages. Although treatment of bermudagrass forages with microbial inoculant had no effect on silage in vitro or in situ NDF disappearance at 48 h of incubation, it increased in situ NDF disappearance at 72 h ( p < 0.05) and the potentially digestible fraction of NDF. It is concluded that the greater cellulose content of cell walls with the same or less lignin in T85, and the greater concentration of ether-linked ferulic acid in CBG explain the greater digestibility of T85 when compared with CBG at similar stages of maturity. Treatment of bermudagrass forage at ensiling with microbial inoculants may have more potential than extracts of fibrolytic enzymes in improving silage fiber digestion.