A bolus for oral administration to an animal, the bolus comprising at least one beneficial substance to be delivered to the animal, the bolus comprising two components which are adhered together by a water-soluble adhesive or sealant, such that the two components are separable in vivo wherein at least one of the aforesaid components is frangible in vivo, the frangible component 2 being initially stabilised by the adherence thereto of the other of the aforesaid components (4), such that separation of the two components facilitates the breakage of the frangible component. Preferably, the frangible component comprises a relatively thin zone or region 20. Preferably, one component comprises a cobalt-containing compound and the other comprises a selenium-containing compound. Also disclosed is a method of making said bolus, the method comprising the steps of forming the first and second components, adhering them together using a water-soluble adhesive wherein at least one of said components is frangible in vivo and is stabilised by the adherence of the other component. The adhesive is dissolved in the digestive tract thereby allowing separation of the stabilising bolus component from the frangible component and subsequent fragmentation of the frangible component.
