Abstract: 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.