Dietary Magnesium Oxide Interactions with Sodium Bicarbonate on Cows in Early Lactation

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Abstract
Holstein cows (36) were fed a diet of 50% concentrate and 50% corn silage (dry matter) for 12 wk postpartum. Treatments were 0, 0.4 and 0.8% MgO with or without 0.8% NaHCO3 in a 2 .times. 3 factorial arrangement. Dry matter intake was not different among treatments although the combined buffers had higher intake. Milk production was higher for the 0.4% MgO treatments alone or with NaHCO3 as compared with the 0 or 0.8% MgO treatments. Ruminal pH was increased with addition of NaHCO3 alone or together with MgO. Dietary addition of 0.4% MgO alone or with NaHCO3 increased total volatile fatty acid in ruminal fluid. Propionate and valerate were depressed in both combined buffered diets. Fecal pH was increased with MgO addition alone or with MgO. Increasing magnesium oxide increased magnesium in plasma. No interactions in animal performance were significant for the 2 buffers.