Microparticles or granules intended for use in the zootechnical field, constituted by a core which contains a substance having a pharmacological action, a food supplement or a diagnostic medium, intimately mixed or adsorbed with a hydrated silicate of magnesium, aluminum, calcium and sodium (smectite, montmorillonite or bentonite); the core is coated with a double fatty layer constituted by two fats or waxes, of which the one having the highest melting point constitutes the inner layer while the one having the lowest melting point is arranged so as to form the outer layer. The ability to control release effectively and accordingly reduce rumen degradation of active substances which contain a cationic or an anionic chemical function, such as for example choline chloride lysine hydrochloride, calcium chloride, citric acid, ascorbic acid or nicotinic acid is determined by the synergistic action of two phenomena: an interaction between the active substance and the other component of the core, and the barrier effect of the double fat layer. Taken individually, the two phenomena are unable to apply effective control over the release of the active substance.