Rumen degradation of some Leguminosae and Graminae roughages: effect of chemical pretreatment with or without cellulase preparation on dry matter and cell wall disappearance

Abstract

Roughages (cowpea husk, maize stover, orchard grass hay and rice straw), which have similar contents of lignin, acid detergent fibre and cellulose, were chemically pretreated with either 50 g NaOH or 50 g alkaline (NaOH) solution of hydrogen peroxide kg −1 dry matter (DM) with or without 5 g cellulase kg −1 DM. Cell wall neutral detergent fibre (NDF) and silica content of the legume increased while those of the grasses solubilised on treatment with NaOH or sequential treatment of NaOH and cellulase. Samples of each preparation were incubated in polyester bags in the rumens of three sheep to estimate degradability. The data were described using the equation p = a + b (1 − e − ct )where p is degradability at time ( t) and a, b and c are constants. All roughages were extensively solubilised in water after chemical treatment, and further solubilised by subsequent cellulase treatment ( P < 0.05). Cellulase preparation significantly reduced ( P < 0.05) lag time during which microbes colonized the cell wall particles. When time effects in fermentation were compared, they were significant ( P < 0.01). Sequential treatment of NaOH and then cellulase was the most effective and increased dry matter and cell wall degradability in the graminaceous plant materials (particularly rice straw) more than the legume ( P < 0.05). The rate of degradation (constantc) was faster for the legume (14.5% h −1) than for the grasses (approximately 4.2% h −1) ( P < 0.01). NDF and DM degradability, silica and DM degradability, hemicellulose and cell wall degradability were positively correlated for cowpea husk ( r from + 0.52 to + 0.84), but negatively correlated for all graminaceous roughages ( r from −0.46 to −0.99).