Effects of sodium bicarbonate on nitrogen balance, bacterial protein synthesis and sites of nutrient digestion in sheep.

Two experiments were conducted to determine effects of sodium bicarbonate (NaHCO3) on nitrogen (N) balance, ruminal N metabolism and site and extent of nutrient digestion in sheep fed 75% concentrate diets. A 2 X 2 factorial arrangement of treatments was employed in both trials with experimental diets balanced for 10.5 or 12.0% crude protein and containing 0 or 3.5% NaHCO3. In experiment 1, 12 lambs were allotted to four diets for two periods in a randomized complete-block design. Dry matter (DM) digestibility was increased (P less than .10) by NaHCO3 supplementation, but organic matter (OM) digestibility was unaffected by treatment. Apparent N digestibility was not affected by NaHCO3 addition but was increased (P less than .0001) at the higher level of protein. Ruminal pH (4 h postfeeding) was increased (P less than .01) by NaHCO3 supplementation. Sodium bicarbonate had no effect on molar proportions of acetate or propionate, but increased molar proportion of butyrate (P less than .10) in ruminal fluid. Mean N retention (g/d) was increased (P less than .05) at the higher protein level, but was not affected by NaHCO3. In experiment 2, four ruminal- and duodenal-cannulated wethers were utilized in a 4 X 4 Latin square design. Sodium bicarbonate addition increased ruminal pH (P less than .05) 2 h postfeeding but did not affect ruminal ammonia (NH3) levels, total VFA concentration or ruminal fluid dilution rates. Molar proportion of acetate was increased (P less than .01) by NaHCO3 at the lower protein level. Ruminal particulate dilution rates were increased (P less than .05) by NaHCO3 addition. Ruminal, postruminal and apparent total tract digestibilities of OM and neutral detergent fiber (NDF) were unaffected by NaHCO3 supplementation. Sodium bicarbonate decreased (P less than .05) ruminal starch digestion at the lower protein level but increased (P less than .05) it at the higher protein level. Bacterial N flow (g/d) at the duodenum and efficiency of bacterial protein synthesis were increased (P less than .10) by NaHCO3 additions.