Nitrogen digestion in the rumen and small intestine of steers grazing orchardgrass and meadow fescue pastures

摘要

Four Holstein steers fitted with cannulas in the rumen, proximal duodenum and distal ileum were rotationally grazed on orchardgrass (Dactylis glomerata L., OG) and meadow fescue (Festuca pratensis Huds., MF) pastures from May to October and examinedfor nitrogen (N) degradation in the rumen, N flow to the duodenum and digestion in the small intestine. N intake on MF pasture was higher than that of OG pasture and was different among the experimental periods. The dietary N degradability in the rumenincreased with increase in N content in herbage and it was negatively related to NDF and neutral detergent insoluble N (NDIN) content in herbage. Non-ammonia nitrogen (NAN) flow to duodenum did not increase linearly with increase of N intake due to the increase of N absorption from the rumen. The proportion of NAN flow to duodenum to N intake was negatively related to the proportion of rumen degradable N to the intake of OM truly digested in the rumen. There was a significant difference in N digestibility in the small intestine between OG and MF pasture (P<0.01). N absorption from small intestine was influenced by the acid detergent insoluble N (ADIN) content in the herbage and the amount of N flow to duodenum. N absorption was higher in steers grazingOG pasture than in steers grazing MF pasture.