| Utilization of minerals from forages by ruminants occurs through two processes. First, the mineral must be released from the forage. Then once in the ruminal fluid, the mineral can be absorbed by the animal or used by ruminal microbes. The in situ technique was used in experiment one to estimate the immediately and slowly released fraction for calcium, magnesium, potassium, phosphorus, copper and zinc from six forage species. The forages, alfalfa, rhizoma peanut, dwarf elephant-grass, bermudagrass, bahiagrass and limpograss, were evaluated after ruminal incubation in 17 x 9 cm dacron bags for 2, 4, 6, 12, 18, 24, 30, 36, and 72 h. In experiment two, mobile dacron bags, 8 x 3 cm in size, were used to measure postruminal mineral release from these six forage species. Experiment three measured the influence of ruminal pH and energy concentration of the diet on mineral release from alfalfa.;In situ ruminal mineral release varied with forage species and mineral. Mean extent of ruminal mineral release across forage species was as follows: potassium (100%) ;The rumen was the major site of release for all six minerals. Maximal digestive tract mineral release from the six forage species was potassium (100%), magnesium (96%), phosphorus (92%), and calcium (75%). Acid-pepsin incubation increased calcium release an additional 12.5 to 53 percentage units, while lower-tract incubation increased phosphorus release an additional 2.6 to 14.1 percentage units across all forage species.;Energy concentration of the diet and ruminal pH affected ruminal mineral outflow. More of the calcium (55 vs. 40%) and phosphorus (86 vs. 77%) leaving the rumen was in the liquid phase when readily fermentable carbohydrates were in the diet. Apparent absorption of potassium was decreased by acid infusion or supplemental energy. |
