Change in nitrogen fractions and ruminal nitrogen degradability of orchardgrass and alfalfa during the ensiling process and the subsequent effects on nitrogen utilization by sheep

In order to determine the extent of change in nitrogen fractions and in vitro ruminal degradability of forage protein during ensilage and the influence on nitrogen utilization by sheep, orchardgrass (Dactylis glomerata L.) and alfalfa (Medicago sativa L.) were ensiled in separate 120 L silos for 5, 21 and 56 days. With respect to nitrogen fractions, fraction 1 (buffer solution soluble nitrogen), fraction 2 (buffer solution insoluble nitrogen-neutral detergent insoluble nitrogen), fraction 3 (neutral detergent insoluble nitrogen-acid detergent insoluble nitrogen), and fraction 4 (acid detergent insoluble nitrogen) were determined. Fractions 1 and 2 accounted for more than 80% of total nitrogen in orchardgrass and 90% of that in alfalfa. The proportion of fraction 1 in orchardgrass increased from 33.0% at day 0 to 52.0% after day 56 of ensiling. In the case of alfalfa silage it was 41.7% and 62.9%, respectively. Seventy percent of this increase occurred within the first 5 days of ensiling. A similar change of in vitro ruminal degradability of total nitrogen was also observed in both forages. Nitrogen retention in sheep tended to decrease as the length of ensiling increased, with a significantly positive correlation between urinary nitrogen and fraction 1, and in vitro ruminal degradability of total nitrogen.