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In order to evaluate the ruminal degradation of Paspalum notatum (grass pasture) in rumen of bovines at different times of the year, in a field of northeastern Argentina, samples of this pasture were collected at 15, 30 and 45 days of regrowth, were cut and placed 5 g in dacron bags, to be introduced in the rumen at 120, 72, 48, 24, 12, 6, 3 and 0 hours, and removed at the same time, an aliquot was fixed in aceto-alcoholic formalin solution (FAA), dehydrated with acetone and mounted on aluminum foil and metallized for observation in scanning microscope (MEB). The degradation of the tissues was determined according to the state of the cell walls. Four categories were established: D: highly degraded; DA: advanced degradation; PD: partially degraded; ND: not degraded. In autumn, the cut from 15 days to 12 hours, the disappearance of the chlorenchyma (mesophyll) was advanced and the phloem beganto be digested. After 48 hours, some paranchymal cells of the beam sheath remained undigested. At 30 days and 48 hours of incubation, mesophyll and phloem suffered complete degradation. At 45 days instead, he only showed a complete digestion for the chlorenchyme, the phloem presented advanced digestion. In winter, at 24 hours on lythex ylem tissues and abaxial sclerench y maremained. After 48 hours in rumen the only thing not digested was xylem, sclerenchyma and sheath of the beam. The mesophyll and the phloem, at 15 days and 24 hours, were digested 100%, for 30 and 45 days, advanced digestion was observed. In spring, the three ages showed chlorenchyme, phloem, and partially degraded sheath at 12 hours, the 24-hour the reveal e advanced degradation and complete digestion after 48 hours. The xylem, was degraded in it sentir et y to 48 hours of the cut of 15 days, instead for 30 and 45 days, the degradation was advanced . In summer the behavior was similar to spring. In general terms the anatomical characteristics observed, in the thre eages of cut and different seasons were variable fort his species. [ABSTRACT FROM AUTHOR]