EFFECT OF LINSEED OIL SUPPLEMENTATION ON FEED DEGRADATION AND MICROBIAL SYNTHESIS IN THE RUMEN OF CILIATE-FREE AND REFAUNATED SHEEP

The consequences of a 6% linseed oil (LSO) supplementation on fibre digestion and microbial protein synthesis in the rumen were investigated in ciliate-free and refaunated sheep, in order to assess the role protozoa depletion plays in the various effects of oil feeding. The incorporation of LSO in the diet decreased protozoal numbers from 565 X 10(3) ml-1 to 191 X 10(3) ml-1 (P < 0.01). It did not modify significantly the rumen fluid kinetics. Defaunation and the supply of LSO shifted rumen fermentation to a higher propionate/acetate molar ratio. Digesta flows at the duodenum were measured using ytterbium as a flow marker. The addition of LSO significantly reduced the digestion of hemicelluloses in the rumen, mainly by a direct inhibition of bacterial activity. Flow of microbial matter at the duodenum was estimated using 2,4-diaminopimelic acid or purine bases as microbial markers. Both defaunation and LSO supplementation decreased the amount of OM apparently digested in the rumen and increased the flow of microbial nitrogen at the duodenum, leading to an increase in the efficiency of microbial protein synthesis.