Effects of rapeseed oil on rumen enzyme activity and in sacco degradation of grass silage

Abstract

The effects of rapeseed oil (double zero variety, 00) supplement (RSO) on rumen protozoal, microbial carboxylmethylcellulase (CMCase) and xylanase activity was studied on four rumen-fistulated Friesian bulls in a 2×2 changeover design. Each experimental period lasted 21 days. The basal diet was 4.8 kg day −1 dry matter (DM) fresh cut grass silage and 2.6 kg day −1 DM rolled barley. The test feed (RSO) was formulated by supplementing the basal diet with 0.5 kg crude rapeseed oil. Crude RSO contained 98.2% fatty acids and was mixed daily with rolled barley manually. Feeding took place twice a day at 07:00 and 19:00 h. Drinking water was available at all times. In sacco rumen degradability of RSO-treated (RSOT) and untreated (UTS) fresh cut grass silage was determined on both basal and RSO diets during both periods. A daily supplement of 0.5 kg RSO had no effect ( P = 0.53) on rumen pH but decreased ( P = 0.01) protozoal mass (gl −1). It also depressed ( P = 0.07) rumen digesta CMCase and xylanase ( P = 0.01) activities. Carboxylmethylcellulase and xylanase activities from rumen-incubated grass silage fibre was depressed by both dietary RSO and RSO treatment of grass silage prior to incubation. In sacco degradability of grass silage DM, neutral detergent fibre (NDF) and acid detergent fibre (ADF) was lowered both by dietary RSO and RSO treatment of grass silage prior to rumen incubation. However, RSO treatment of grass silage was not as effective in fibre degradation as dietary RSO. The value for the soluble fraction ( a) of RSOT silage NDF and ADF was negative on both diets, whereas the value for the insoluble, potentially degradable material ( b), was high for RSOT silage. Lag time was extended by both dietary RSO and RSO treatment of silage prior to rumen incubation. The relationship of rumen CMCase and xylanase activity levels to in sacco NDF degradation of both RSOT and UTS on both diets was linear ( r = 0.97).