Abstract: A dosage form for administering physiologically active substances to animals, especially ruminant animals. The dosage unit includes a core which contains the active substance and a coating. The coating has selected areas which are thinner than the average thickness of the coating and/or areas which are predetermined rupture sites. These thin areas or predetermined rupture sites are constructed and arranged so as to detach and/or rupture under the conditions which are present after oral administration of the dosage form. As a result, the delayed release of the physiologically-active substance is accelerated. For example, the coating may be formulated to not be affected in the first stomach of a ruminant but to rapidly disintegrate in the animal's second stomach.