Effects of sodium bicarbonate and calcium magnesium carbonate supplementation on performance of high producing dairy cows

Sodium bicarbonate (SB) is a common dairy feed supplement, although recent research on its rumen buffering efficacy in contemporary dairy diets with low starch levels is limited. In California, and other areas of the world, new environmental regulations aim to minimize the amount of fixed solids (FS), including Na, which are discharged from dairy farms. Our aim was to determine effects of SB or calcium magnesium carbonate (CMC; a potential alternative buffer which does not contribute to Na discharge), on performance of early lactation high producing Holstein cows. The study was a Latin square design with 3 periods of 28 d, 3 treatments (i.e., control (C), SB, CMC) and 3 pens of ∼310 cows. The total mixed ration was supplemented with 8 g/kg dry matter (DM) of SB or CMC, and contained 519 g/kg DM and 158 g/kg crude protein (CP), 334 g/kg aNDF (i.e., neutral detergent fiber assayed with a heat stable amylase expressed inclusive of residual ash) and 160 g/kg starch (DM basis). The dietary cation anion difference (DCAD) for the C, SB and CMC supplemented diets was 375, 456 and 381 mEq (Na + K − Cl)/kg DM, respectively. The DM intake for C, SB and CMC cows did not differ (28.2, 28.5, 28.6 kg/d, respectively), but the SB supplemented diet tended (P=0.053) to reduce DM digestibility (637 versus 656 g/kg DM) and increase (P=0.09) fecal pH (6.65 versus 6.60) compared to C. The CMC supplemented cows had higher (P<0.001) fecal pH than C cows (6.76 versus 6.60), but digestibility did not differ. SB supplemented cows had lower (P<0.01) milk yield (45.2 versus 46.2 kg/d) and higher (P<0.01) milk fat (35.6 versus 34.3 g/kg), but milk fat yield did not differ (1.60 versus 1.58 kg/d) compared to C. The C and CMC supplemented cows did not differ in milk yield (46.2 versus 45.7 kg/d) or composition. Changes in body condition score were similar for C and SB supplemented cows, but tended (P=0.08) to be lower for CMC versus SB supplemented cows (−0.07, −0.09, −0.03 units/30 d for C, SB and CMC cows, respectively), and net energy (NEl) output (172.4, 170.9, 173.2 MJ/d), and diet NEl concentration (6.12, 6.00, 6.06 MJ/kg DM) for C, SB and CMC supplemented diets did not differ. Results suggest that SB buffered the rumen and/or improved acid base balance by increasing DCAD, and that CMC buffered the abomasum and lower gastrointestinal tract. However, for diets and conditions comparable to this study, use of neither SB nor CMC is supported due to similar animal performance.