Abstract: A porous water soluble glass body is formed by sintering powdered glass, compacted to a predetermined density, at a temperature near the glass softening temperature (T.sub.s). The porous body may be impregnated with an organic material for subsequent release at a rate determined by the glass solubility.

Abstract: A rumen bolus for supplying a mineral supplement to a ruminant animal comprises a water soluble glass incorporating the mineral and contained in an apertured insert, e.g. plastics, housing. Typically the glass is in the form of tubes or pellets so as to provide a substantially constant dissolution rate.

Abstract: A copper phosphate water soluble glass composition. The composition of the glass may be adjusted so as to release copper at a uniform preselected rate and to produce a desired pH in the resultant solution. In one application of the glass copper may be supplied to an animal from an implant formed from a cupric oxide/phosphorus pentoxide glass which also incorporates one or more glass modifying oxides such as alkali metal oxides and alumina, to control the glass solubility. Suitable glasses comprise 5-55 mole % cupric oxide + alkali metal oxides. 45-75 mole % phosphorus pentoxide, and not more than 15 mole % alumina, where the copper oxide concentration is not less than 5 mole %.