The average particle size (PS) and module of fineness (MF) of the diet, ruminal digesta and feces of steers, as well as relative resistance (RR) of the particles to escape of the reticulum-rumen, were studied in a native pasture of the Zona da Mata - Minas Gerais State, during the Season 1 (S1), that corresponded to the months of February/March/April, and Season 2 (S2), that corresponded to the months of August/September/October. The PS and MF of the diet selected by the bovine did not vary among the S1 (1.91 mm and 3.62) and the S2 showed (2.10 mm and 3.72). In the S1, PS and MF of the ruminal digesta linearly decreased until the 24 hours time, while, in the S2, presented a quadratic response, increasing up to a maximum of 1.62 mm and 3.31 in the 13.20 and 12.95 hours, respectively, after beginning of the feeding. For PS and MF of the feces, there was no effect of the collection time, but it were different between the E1 (0.55 mm and 2.09) and E2 (0.45 mm and 1.90) and in the months within the E1 season. The reduction of the particles sizes in the E2 was a restriction factor regulating the exit of digesta from the rumen, and in the E1, it favored the escape of medium particle sizes. A continuous increase in the resistance of the particles to escape from the rumen with the increase of the particle size was noticed; particles larger than 1.19 mm escaped from the rumen, in spite of face strong resistance, and the smaller particles than this size faces different degrees of resistance to escape from the rumen.
module of fineness; native pasture; particle size; relative resistance
