Proteolysis during ensilage of forages varying in soluble sugar content.
The effect of contrasting concentrations of water-soluble carbohydrates of herbage on silage fermentation and composition was examined using grass with high [250 g/kg of dry matter (DM)] concentrations of water-soluble carbohydrates and grass and clover with low (66 g/kg of DM) concentrations of water-soluble carbohydrates. Herbages were ensiled untreated, after inoculation with lactic acid bacteria, or after treatment with formic acid. Good quality silages were produced from herbage with high concentrations of water-soluble carbohydrates, regardless of treatment, and all pH values were below 3.7 after 90 d of ensilage. However, the silage formed from inoculated herbage had a significantly lower concentration of ammonia N and a significantly higher proportion of residual ribulose-1,5-bisphosphate carboxylase compared with the other two silages. Fast protein liquid chromatography (Pharmacia, Uppsala, Sweden) was used to measure ribulose-1,5-bisphosphate carboxylase, and measurement of true plant protein fractions in herbage and silage showed benefits over traditional measurements such as the measurement of N and ammonia N. Herbages with low concentrations of water-soluble carbohydrates produced inferior quality silages that had lower ribulose-1,5-bisphosphate carboxylase contents and higher ammonia N contents, regardless of treatment; few significant differences were observed among treatments. Under good ensiling conditions, when available water-soluble carbohydrate is adequate, the use of inoculants can improve fermentation characteristics and increase the ribulose-1,5-bisphosphate carboxylase content of silages. However, when the herbage has low concentrations of water-soluble carbohydrates, even in inoculated herbages, lactic acid bacteria may follow a heterofermentative pathway instead of a homofermentative pathway, which can result in a decrease in silage quality and a reduction in intact ribulose-1,5-bisphosphate carboxylase.
Davies
D R
DR
Institute of Grassland, Aberystwyth, Ceredigion, United Kingdom.
Merry
R J
RJ
Williams
A P
AP
Bakewell
E L
EL
Leemans
D K
DK
Tweed
J K
JK
D000641:Ammonia / Q000032:analysis; D002241:Carbohydrates / Q000032:analysis*; D002851:Chromatography, High Pressure Liquid; D010450:Endopeptidases / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007778:Lactobacillus / Q000378:metabolism; D009584:Nitrogen / Q000032:analysis; D010940:Plant Proteins / Q000032:analysis; D006109:Poaceae / Q000737:chemistry; D012273:Ribulose-Bisphosphate Carboxylase / Q000032:analysis; D012820:Silage; D012995:Solubility
D002241:Carbohydrates; D010940:Plant Proteins; D000641:Ammonia; D010450:Endopeptidases; D012273:Ribulose-Bisphosphate Carboxylase; D009584:Nitrogen