Ready-made supplementary feed for horses that is also suited to prophylaxis or therapy of the muscle metabolism condition PSSM, contains 5-25 weight % rice meal and/or rice bran, 12-30 weight % supplying vegetable fat constituents, 20-40 weight % of green meal, 20-40 weight % of sugar beet seeds. The constituents supplying vegetable fat contain approximately 10 weight % of at least one of black and striped sunflower seed kernels, 2 weight % of soy bean oil, 3 weight % of linseed cake and 3 weight % of linseed oil. The feed can also contain approximately 5 weight % dried pulp, 5 weight % apple residue, 5 weight % of at least one of brewer's yeast and soy grits.