Comparison of the in situ degradation parameters of fresh and frozen-thawed 15N-labelled alfalfa and ryegrass

Degradation of dry matter (DM) and nitrogen (N) in fresh or frozen-thawed alfalfa and ryegrass was studied by using in situ technique. The forages were labeled with 15N during growth in a glasshouse, harvested at similar growth phase, and fresh (F) or frozen-thawed (FT) samples were incubated in the rumen of 3 sheep. There was no difference (P>0.05) between forage type (S) for the immediately soluble fraction (a) and the insoluble but slowly degradable fraction (b) estimates for DM and N disappearance over time. However, 15N values for a and b were significantly (Pb (c) and potential degradability of DM, N and 15N; degradation rate of b for DM, N and 15N were higher for alfalfa. There was no effect due to sample preparation (M) in degradation rate (c) for DM and 15N but FT had a significantly (P15N. Mean estimates of effective rumen degradable protein due to forage species were significantly (Pin situ degradation determination the same preparation method be used throughout.