Effect of selected dietary buffers upon utilization of concentrate- or roughage-based cattle diets: laboratory...

Four chemical buffers were evaluated with in vitro rumen fermentation studies using both an 80% concentrate and a 50% roughage diet. Treatments included a positive control (PC), negative control (NC) and four buffered diets in which 500 mg of either CaHPO4, CaCO3, NaHCO3 or Na4P2O7 were added. The PC consisted of unbuffered diet with one part rumen fluid and four parts McDougall's artificial saliva. In the unbuffered NC and buffered treatments, three-fourths of the artificial saliva was replaced by iso-osmotic saline. In the concentrate-based diet, NaHCO3 and Na4P2O7 elevated (P less than .05) pH above the NC. Starch digestion and total VFA were increased (P less than .05) by NaHCO3 compared with the NC while the molar proportion of individual VFA was not altered. Tetrasodium pyrophosphate had no effect on starch digestion or total VFA, but did increase (P less than .05) the molar proportion of acetic acid. Regarding the 50% roughage diet, both NaHCO3 and Na4P2O7 elevated (P less than .05) starch and cellulose digestion and total VFA compared with the NC. Both NaHCO3 and Na4P2O7 increased (P less than .05) the molar proportion of acetate to equal that of the PC. Tetrasodium pyrophosphate decreased (P less than .05) apparent starch digestion compared with the NC, but increased (P less than .05) the molar proportion of acetate. Compared with the NC, CaHPO4 and Na4P2O7 increased the quantity of microbial alpha-amino N in both diets. Soluble P was highly correlated with microbial protein synthesis in both the concentrate- and roughage-based diets (.92 and .90, respectively).