PROTEOLYSIS DURING ENSILAGE OF FORAGES VARYING IN SOLUBLE SUGAR CONTENT

The effect of contrasting concentrations of water-soluble carbohydrate s 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) c oncentrations of water-soluble carbohydrates. Herbages were ensiled un treated, after inoculation with lactic acid bacteria, or after treatme nt with formic acid. Goad quality silages were produced from herbage w ith high concentrations of water-soluble carbohydrates, regardless of treatment, and all pH values were below 3.7 after 90 d of ensilage. Ho wever, the silage formed from inoculated herbage had a significantly l ower concentration of ammonia N and a significantly higher proportion of residual ribulose-1,5-bisphosphate carboxylase compared with the ot her two silages. Fast protein liquid chromatography(R) (Pharmacia, Upp sala, Sweden) was used to measure ribulose-1,5-bisphosphate carboxylas e, and measurement of true plant protein fractions in herbage and sila ge showed benefits over traditional measurements such as the measureme nt of N and ammonia N. Herbages with low concentrations of water-solub le carbohydrates produced inferior quality silages that had lower ribu lose-1,5-bisphosphate carboxylase contents and higher ammonia N conten ts, regardless of treatment; few significant differences were observed among treatments. Under good ensiling conditions, when available wate r-soluble carbohydrate is adequate, the use of inoculants can improve fermentation characteristics and increase the ribulose-1,5-bisphosphat e carboxylase content of silages. However; when the herbage has low co ncentrations of water-soluble carbohydrates, even in inoculated herbag es, lactic acid bacteria may follow a heterofermentative pathway inste ad of a homofermentative pathway, which can result in a decrease in si lage quality and a reduction in intact ribulose-1,5-bisphosphate carbo xylase.