The invention relates to a feed additive for ruminants, comprising ammonium sulphate and a water extract of sweet chestnut wood, comprising sweet chestnut tannins. The feed additive may be in granular form or in liquid form The amount of ammonium sulphate in the feed 5 additive is such that between 30 and 300 gram/day of ammonium sulphate is fed to a bovine, and an amount of sweet chestnut extract between 1 and 20 gram/day, preferably below 9 mg/day/bovine.
