In situ degradation of perennial rye grass from grazed pastures during the season at two levels of nitrogen fertilization

Abstract

In situ incbations were carried out to investigate the effect of rate of nitrogen fertilization and season on rumen degradation of ryegrass. Samples of Lolium perenne of grazed herbage, fertilized at two levels of nitrogen (250 and 550 kg N/ha/year), were collected in May, July-August, September and October, and incubated in nylon bags in the rumen of three grazing dairy cows with a rumen cannula. Theoretical degradability in the rumen varied between 56 and 64% for organic matter, between 60 and 71 % for crude protein and between 59 and 74 % for neutral-detergent fibre. Theoretical degradability was lower in summer than in spring and especially in autumn (P < 0.001). Reducing N fertilizer application decreased the theoretical degradability in the rumen (P < 0.001). Differences between rates of N application were less pronounced in autumn. © Elsevier / Inra.