Influence of pH and rapidly fermentable carbohydrate on mineral release in and flow from the rumen.

Objectives for this study were to determine the effect of energy supplementation on mineral release in and outflow from the rumen, independent of pH. Nonlactating Holstein cattle with ruminal cannulas were limit-fed chopped alfalfa hay with or without energy supplement. Treatments were 1) control, alfalfa plus ruminal infusion of 3 L/d of distilled water; 2) acid, alfalfa plus infusion of 3 L/d of 1N HCl; 3) energy supplement, alfalfa and ground corn plus infusion of 3 L/d of distilled water; and 4) buffered energy supplement, alfalfa, and ground corn plus infusion of 3 L/d of distilled water containing 90 g of NaHCO3. Macromineral intake was standardized across treatments by adjustment of infusion solutions with inorganic mineral sources. Dry matter consumed was 5 kg/d on treatments 1 and 2 and 8.4 kg/d on treatments 3 and 4. Mean ruminal pH was 6.8, 6.1, 5.6, and 6.2 for treatments 1 through 4, respectively. Ruminal pH was more significant than energy supplementation in dispersion of Ca, Mg, and P in ruminal digesta. Only 1, 17, and 27% of dietary K, Mg, and P flowed with solids from the rumen, but 52% of Ca and 41% of Cu remained with the solid phase.