Compositions for coating feeding stuff additives intended for ruminants and feeding stuff additives thus coated

A composition suitable for coating a bilogically active substance, which is stable at a pH greater than or equal to 5 and which permits the release of the biologically active substance at a pH less than or equal to 3.5, which composition comprises:

• 40 to 95% by weight of a film-forming, waterinsoluble binding agent which possesses controlled hydrophilicity and which may be slightly sensitive to pH variations, the said binding agent being selected from the group consisting of a combination of a water-insoluble filmforming cellulose derivative and an agent for controlling the hydrophilic/hydrophobic balance selected from the group consisting of polyols in a weight ratio of cellulose derivative to polyol of from 1:1 to 1.5:1;
• zein;
• and a combination of zein and an agent for controlling the hydrophilic/hydrophobic balance selected from the group consisting of water-insoluble cellulose derivative in a weight ratio of 2:1 to 10:1;
• and 60 to 5% by weight of a pH sensitive substance selected from the group consisting of a polymer or copolymer containing at least one basic amino group and having a nitrogen content between 2 and 14% selected from the group consisting of amino derivatives of cellulose, polymers of amino derivatives of acrylic and methacrylic acids, copolymers of styrene with a vinylpyridine, and chitosan.