INFLUENCE OF FORAGE SPECIES AND DIET PARTICLE-SIZE ON THE PASSAGE OF DIGESTA AND NYLON PARTICLES FROM THE RETICULORUMEN OF STEERS

To assess factors that influence the passage of digesta from the retic ulorumen, ruminally fistulated steers (387 kg) were fed to appetite in a 4 x 4 Latin square design either orchardgrass (OG) (Dactylis glomer ata L.) or switchgrass (SG) (Panicum virgatum L.) hays. The two hays w ere fed in either the long form or ground to pass a 2-cm screen. Steer s fed OG diets had greater DMI (P < .05) than steers fed SG diets (11. 7 vs 10.4 kg/d respectively). Particle size of ruminal digesta and fec es determined by wet sieving was greater (P < .05) for the OG and long hay diets than for the SG and ground diets. Particle size of digesta collected from the anterior dorsal sac and anterior ventral sac of the rumen and from the reticulum did not vary (P > .25) with site. Conver sely, ruminal concentrations of 1-mm nylon particles tended ( P = .11) to be greater in the lower strata of the reticulorumen at 12 and 24 h after dosing. Neither a site effect nor a site x time-after-dosing in teraction (P > .75) was observed for the 3- or 5-mm nylon particles, s uggesting that a sorting process independent of specific gravity occur s in the rumen for smaller particles (before the reticuloomasal orific e). Passage rate of the 1-mm nylon particles from the reticulorumen wa s greater ( P < . 0 1) for animals fed the SG than for those fed the O G diets, whereas for the 5-mm particles, passage rate was greater for the OG diets. Particle size of the diet did not influence passage (P > .15) of the nylon particles, although it influenced (P < .05) particl e size of the ruminal and fecal samples to the same extent as forage s pecies. Therefore, it seems that differences in passage rates of the n ylon particles influenced by forage type were a result of factors othe r than ruminal particle size.