Batch cultures of mixed rumen microorganisms were used in a randomized complete block design to study the effects of alfalfa hay-to-concentrate ratio and various non-organic buffering compounds on Acidogenic Value (AV), in vitro dry matter disappearance (IVDMD), medium pH, and AV: IVDMD ratio. Alfalfa hay was included in the experimental diets as: 80% (F80), 60% (F60), 40% (F40), and 20% (F20) on a dry matter (DM) basis. Buffering compounds were added to the experimental diets as: Sodium bicarbonate [SB; 5 or 10 mg.g-1 DM], magnesium oxide (MgO; 5 or 10 mg.g-1 DM), sodium bentonite (bentonite;10 or 20 mg.g-1 DM), Acid Buf® (5, 10 or 20 mg.g-1 DM), Acid Buf + SB in a 3:4 ratio (11 or 16.5 mg.g-1 DM), Acid Buf + SB + MgO in a 3:4:1 ratio (12.5 or 18.75 mg.g-1 DM), and Herod’s Buffer (5, 10 or 20 mg.g-1 DM); keeping one group as control (no supplementation). After 24 h incubation, no significant differences observed in medium pH among SB, MgO, bentonite and the control, but Herod’s Buffer, Acid Buf, Acid Buf + SB, and Acid Buf + SB + MgO kept it up (P≤ 0.05). The lowest AV and AV: IVDMD ratios were observed when SB was used in the cultures (P≤ 0.05). Herod’s buffer IVDMD was the lowest (P≤ 0.05). The results indicated that the diet containing Acid Buf and SB had a relatively low AV and AV: IVDMD, and could maintain a relatively high rumen fluid pH compared with those of the others.

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