Effect of ensiling on the ruminal degradability and intestinal digestibility of the corn forage

摘要

The effective degradability (ED) and the intestinal digestibility (ID) of dry matter (DM) and crude protein (CP) of a green corn crop (GC) and its silage (CS) were determined using in situ and particle transit techniques on three whethers cannulated in rumen and duodenum. Two rumen incubations with duplicates of bags at times of 0, 2, 4, 8, 16, 24, 48 and 72 h were performed for each feed, under conditions of continuous infusion in the rumen of a salt of ~(15)N. For each incubation, one bag was ovendried (80°C, 48h) to determine rumen degradation and the other bag was freeze-dried. These last samples were pooled for each rumen incubation time and 2 sub-samples were incubated into mobile nylon bags through the intestine of each animal. To determinethe effective ID (EID), the above-pooled residues were composited in accordance with the rumen outflow and the kinetic of DM degradation to simulate the rumen flow. Then 4 sub-samples per animal were essayed by the same procedure. The ED values (%) obtained for GC and CS were respectively 53.1 and 57.7 (M.S.E.=0.63; P<0.05) for DM and 71.7 and 68.1 (M.S.E.=0.89; P=0.1) for CP. The evolution in the time of the colonization and the contamination fitted well to exponential equations, with higher asymptotic values for CS. The ID values for GC decreased with the time of ruminal pre-incubation for DM (P<0.001) as well as for CP (P=0.057). For CS this effect was only observed on the DM (P<0.001), although an increase was detected at 72h. The evolution of IDfor CP was irregular. The silage reduced the EID of DM (17.8 vs. 14.2%; M.S.E.=0.56; PO.05) as well as of CP (66.7 vs. 52.4%; M.S.E.=1.07; PO.05).