Effects of rape-seed oil supplementation on digestion, microbial protein synthesis and duodenal microbial amino acid composition in ruminants

Abstract

The effects of rape-seed oil supplementation on digestion and efficiency of microbial protein synthesis were estimated in four Friesian bulls fitted with rumen and simple-T duodenal fistula in 2 × 2 change-over design. 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 rape-seed oil. The bulls were fed at 07:00 and 19:00 h daily. Digestion in the rumen was measured by spot sampling of duodenal digesta, using the double marker method. Amino acid (AA) composition was determined from the microbial mass separated from duodenal digesta. A daily supplement of RSO showed no significant effect on rumen pH. Rumen total volatile fatty acids concentration decreased ( P = 0.09). Molar proportion of acetate and butyrate decreased ( P = 0.01) while propionate proportion increased ( P = 0.002). Rumen protozoal population decreased from 4.2 × 10 5 to 2.9 × 10 51 −1. Whole tract and ruminal digestion of organic matter was lower for RSO compared with basal diet. The mean N intake was 160 g day −1 for basal and 153 g day −1 for RSO and the corresponding duodenal flow was 140 g day −1 and 146 g day −1 with microbial N flow of 78 g day −1 and 86 g day −1, respectively. Duodenal microbial AA N (g per 100 g microbial N) was 85.0 for basal and 64.6 for RSO with decreased ( P = 0.02) lysine and methionine content of microbial AA. The rate of passage ( K p) was reduced with extended fibre retention time.