Effect of dietary fructose polymers or sucrose on microbial fermentation, enzyme activity, ciliate concentration and diversity of bacterial flora in the rumen of rams

•The effect of fructose-enriched diet on the rumen metabolism was analyzed.•Enrichment of the diet with fructose did not influence the total SCFA concentration.•Enrichment of the diet decreased the acetate and increased butyrate levels.•The activity of carbohydrate-digesting enzymes was not influenced by the diet.•Enrichment of the diet selectively affected protozoa but not eubacteria populations.