CORN-SILAGE SUPPLEMENTATION OF COWS GRAZING WINTER OATS - DYNAMICS OF DIGESTION AND RUMINAL ENVIRONMENT

The effect of com silage (Zea mays L.) (CS) supplementation of winter oat (WO) (Avena sativa L.) in grazing conditions on rumen environment and dynamics of digestion were studied. The trial was designed as a cross-over, for two treatments (T0, winter oats only; T1, winter oats and 5 kg of CS (dry matter (DM) basis), two periods and six animals fitted with ruminal cannulae. Animals grazed WO ('in vitro' DM digestibility (IVDMD), 7 1. 1%; crude protein content (CP), 12.8% and neutral detergent fiber (NDF), 40.8%). Animals in T1 ate CS (IVDMD, 64.4%; CP 8.4% and NDF, 50.9%) twice daily (08:00-12: 00 and 14:00-20: 00 h) and then had a routine similar to T0. Rumen fluid pH tended to be higher (P < 0.07) in T1 (6.31 ) than in T0 (6.14). Buffer capacity in the acid range (BC) (Eq. per 1 00 ml) was higher (P < 0.05) in T0 ( 1 0.64) than in T1 (9.42). Ammonia nitrogen concentration and the acetic/propionic ratio were not different while the acetic plus butyrate/propionic ratio tended to be higher (P < 0.08) in T0 (T0: 3.69 and T1: 3.45). In WO the effective protein degradability (PD) was higher (P < 0.05) in T0 (T0: 79.1% and T1: 75.3%) and Period I (Period I: 80.6%, Period II: 72.8%). Of NDF degradation kinetics the lag time was higher (P < 0.05) in T1 (5.8 h) than in T0 (1.4 h) for WO but not for CS. In WO the actual extent of NDF digestion (AED) was not different between treatments but tended to be higher (P < 0.10) for Period I (51.6%) than for Period II (36.6%). In CS the AED was low, and tended to be higher (P < 0.10) in T0) (T0): 27.4% and T1: 23.4%). Com silage supplementation altered rumen fluid pH and BC but had little effect on NDF digestion of both forages. The smaller AED in corn silage can act as a constraint of total DM intake. The period effect in PD and AED in WO suggests that the chemical and structural variations have an important effect on the digestion process.