RUMINAL DEGRADATION CHARACTERISTICS OF CORN AND CORN SUNFLOWER INTERCROPPED SILAGES PREPARED AT 2 STAGES OF MATURITY

The degradation characteristics of dry matter (DM), protein, neutral detergent fiber (NDF) and acid detergent fiber (ADF) of com-sunflower intercrop silage (CSS) and monoculture corn silage (CS) prepared from whole plants, harvested at two stages of maturity, were compared using eight mature rumen-cannulated steers. The degradation characteristics were determined by incubating the silages in nylon bags for up to 72 h in the rumen of animals fed the respective silages. The degradation characteristics determined for the silages were the soluble fraction, the insoluble but degradable fractions, the rate of degradation of the degradable fractions of silage DM and protein, and the in situ disappearance of NDF and ADF after 0.5 and 72 h of incubation. The rate of particulate passage from the rumen was determined using chromium-mordanted NDF of the four silages. Values were used to estimate effectively degraded DM and protein. The rates of DM and protein degradation were highest for late-cut CSS (6.3 and 6.0% h-1, respectively) and the least for late-cut CS (2.5 and 0.8% h-1, respectively). Averaged across stages of maturity, more (P < 0.05) DM and protein were effectively degraded with CSS (57.4 and 70. 1 %, respectively) than with CS (48.8 and 48.7 %). Degradation of NDF in early-cut CSS was lower (P < 0.05) than in CS after 72 h of incubation. ADF disappearance from all of the silages after 72 h of incubation was similar. Ruminal degradation of DM and protein in CSS was greater than in CS, which may affect efficiency of utilization of CSS.