The present invention relates to the use of guanidinoacetic acid and/or salts thereof as feed additive, in predominantly vegetarian diets, in particular use being made of salts with hydrochloric acid, hydrobromic acid and phosphoric acid. The use proceeds especially in individual doses from 0.01 to 100 g/kg of feed in the form of powders, granules, pastilles or capsules, the feed additive also being able to be used in combination with other physiologically active materials of value. The claimed use which is suitable especially for breeding and growing livestock, has recourse to a compound which is in particular stable in aqueous solution, can be converted to creatine under physiological conditions, and, in contrast to other guanidine derivatives, is completely available to physiological sectors of use.
