According to Regulation (EC) No 1831/2003, additives are substances, micro-organisms or preparations, other than feed materials and premixtures, which are intentionally added to feed or water in particular in order to perform, in particular, one or more of the following functions;

a) favourably affect the characteristics of feed;

b) favourably affect the characteristics of animal products;

c) favourably affect the colour of ornamental fish and birds;

d) Satisfying the nutritional needs of animals;

e) favourably affect the environmental consequences of animal production;

f) favourably affect animal production, performance or welfare, particularly by affecting the gastro-intestinal flora or the digestibility of feedingstuff or

g) have a coccidiostatic or histomonostatic effect.

Based on these functions, four categories of additives have been defined (e.g. zootechnical additives, Cat. 4) and a number of so-called functional groups per category (e.g. digestion promoters, Cat. 4a). Additives are only authorized after an extensive risk evaluation by EFSA of the submitted file and publication of an Authorization Regulation (in the event of a positive EFSA assessment) by the European Commission.