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In Vitro Effect of pH Variations on Rumen Fermentation, and In Vivo Effects of Buffers in Lambs before and after Adaptation to High Concentrate Diets¹

South Dakota State University, Brookings 57007

Abstract

An in vitro wheat fermentation study (Exp. 1) was conducted to investigate the effect of pH (pH 7, 6, 5 and 4) on rumen lactate and VFA production. In another study (Exp. 2), lambs were fed high concentrate diets containing either no additions (control), 2% sodium bentonite, 2% limestone, 2% NaHC0₃ or 10% alfalfa hay. The effect of these diets was determined on ruminal and systemic measurements before and after dietary adaptation. Effect of the control, bentonite, limestone and NaHC0₃ treatments on nutrient digestibilities and mineral retentions after adaptation were also determined. Lactate production in the rumen fluid incubated at pH 7 or 6 was negligible. Reducing incubation pH from 6 to 5 resulted in accumulation of both total and L(+)-lactate, but further reduction to pH 4 did not result in an additional increase in lactate production. Variations in incubation pH or time did not affect the ratio of D to L isomers. Lowering the incubation pH to below 6 reduced total VFA production and increased the acetate to propionate ratio. In Exp. 2, the feeding of buffers or alfalfa hay was effective in maintaining a more normal feed intake and ruminal pH, and reduced ruminal lactate. Blood measurements were not affected by dietary treatment. When animals were adapted to the experimental diets, die dietary buffers did not influence rumen and blood measurements. Lambs fed 2% NaHCC>3 digested more (P<.05) organic matter, crude protein, N-free extract and starch, and 2% limestone increased (P<.05) fiber digestibility. Dietary buffers tended to increase fecal pH and reduce fecal starch. Magnesium retention with 2% bentonite, Ca retention with 2% limestone and Na and Mg retention with NaHC0₃ were all increased (P<.05).

¹ Published with approval of the Director of South Dakota Agr. Exp. Sta. as publication 1786 of the Journal Ser.

² Chem. Dept.

³ Anim. Sci. Dept.