Addition of Buffers to High Quality Alfalfa Hay-Based Diets for Dairy Cows in Early Lactation

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Abstract
Beginning 4 wk postpartum, 14 Holstein cows were paired according to expected calving date and lactation number and assigned randomly to 1 of 2 treatments in a single reversal experiment designed to study the effects of added buffers to high quality alfalfa hay-based diets. Cows were offered daily 14.5 kg of concentrate containing 0 or 2% NaHCO3 and 0.5% MgO (as fed), plus free choice high quality alfalfa hay in a ratio of forage:grain approaching 50:50 (dry matter). No differences were found in milk production, milk fat percentage, fat-corrected milk or dry matter intake. Dry matter intake of grain was decreased with addition of buffers. Kilograms fat-corrected milk/kilogram dry matter intake were 1.41 and 1.45 for control and buffered diets. No differences were significant for rumen pH, ammonia concentration, molar proportions of acetate and propionate or ratio of acetate: propionate. Concentrations of total volatile fatty acids were higher for cows fed the buffered diet. No differences were found in blood acid-base status or in various serum metabolites. Urine pH was 8.11 and 8.20 for control and buffered diets. Fractional urinary excretion of Mg and Na was greater when cows consumed the buffered diet. Diet digestibilites and rate of passage were not affected by dietary buffers. Addition of NaHCO3 plus MgO did not improve performance of early lactation cows fed high quality alfalfa hay as the sole forage.