Effects of buffers on ruminal rate of passage and degradation of soybean meal in steers.

Eight rumen-fistulated steers were randomly assigned to medium- and high-concentrate diets supplemented with 0, .75, 2.5 and 5% of either sodium bicarbonate or an artificial saliva salts mixture. Each animal was fed for 21 d at 75 g dry matter/kg body weight . 75. Rates of soybean meal (SBM) degradation were predicted by adjusting digestion rates in nylon bags with respective passage rates of chromium-mordanted SBM particles. Measures of rumen fermentation were made during the incubation period. Liquid dilution rate was determined with 51Cr-EDTA. The high-concentrate diet produced higher (P less than .05) liquid dilution rates than the medium-concentrate diet, but there were no differences in response to the two buffers (P greater than .05). The liquid dilution rates averaged across diets for 0, .75, 2.5 and 5% levels of buffer were 6.2, 6.3, 8.5 and 8.7%/h (SE = .03) and passage rates for SBM were 5.2, 5.2, 6.5 and 6.7%/h (SE = .025). The 2.5 and 5% levels of buffer increased the rate of disappearance of SBM from the nylon bags and buffers fed at these levels also increased rumen pH and NH3-N concentration. Rumen pH was correlated with N disappearance from the nylon bag (r = .903, P less than .05). Buffer levels did not affect degradation rates of SBM.