This work was carried out to evaluate the ruminal degradation of dry matter, crude protein and neutral detergent fiber and ruminal particles and liquid phase dynamics by steers in natural pasture of the Zona da Mata, region of Minas Gerais State, during different seasons of the year. The season 1(S1) corresponded to the months of February/March/April, and the season 2(S2), to the months of August/September/October. Five steers with esophageal and rumen fistulae, each one considered as a replicate, were used in a completely randomized design. The effective degradation of the DM, CP and NDF was higher in the S1 than in the S2. The CP degradation rate showed difference between seasons, being of 2.99%/hours in the S1 and 6.01%/hours in S2. The passage rate was higher in the S1 (4.84%/hours) in relation to S2 (3.59%/hour). The higher undegradable fraction of the nutrients could be the main responsible for the highest retention time and for the ruminal repletion of the fibrous fraction in the rumen. Therefore, the highest ruminal repletion in the S2 (20.93 hours), in relation to S1 (14.84 hours), was probably due more to the physical effect of passage of the high undegradable fraction content, in that season, as compared to the S1, than the microorganisms fermentation.
fiber; natural pasture; passage rate; ruminal degradation; ruminal repletion
