Ruminal release of minerals from six forage species.

An in vitro technique and an in situ technique were used to measure release of Ca, Mg, P and Zn over time from hand-clipped alfalfa (Medicago sativa L.). Maximal release of P and Zn was greater using the in situ technique. 'Florida 77' alfalfa (Medicago sativa L.), 'Florigraze' rhizoma peanut (Arachis glabrata Benth.), 'Mott' dwarf elephantgrass (Pennisetum purpureum Schum.), 'Tifton 78' bermudagrass (Cynodon dactylon (L) Pers.), 'Pensacola' bahiagrass (Paspalum notatum Flugge) and 'Floralta' limpograss (Hemarthria altissima (Poir.) Stapf and Hubbard) were used to examine the ruminal release of Ca, Mg, P, K, Cu and Zn by means of the in situ technique. Minerals were ranked from highest to lowest for extent of immediate and maximal release in the rumen. Averaged across forage species, ranking was K at 100% and 100%, Mg at 82% and 95%, Cu at 71% and 84%, P at 66% and 80%, Zn at 26% and 69% and Ca at 29% and 70%. A large proportion of Ca was associated with the plant cell wall, based on the duration of incubation time needed to maximize its release and the large fractinal amount of Ca slowly released. A large portion of the Zn was released slowly as well (mean, 43.8%), but release of Zn was maximal in less than 24 h. Most of the Mg, K, P and Cu probably reside in the cell contents. Forages with high NDF concentrations can have high release coefficients for their minerals.