A method of promoting or improving the feed efficiency and the muscle to fat ratio in animals by administering to the animals a therapeutically effective amount of a pure or substantially pure RR-isomer of ractopamine is disclosed. Also disclosed are animal feed preparations and compositions and pharmaceutical preparations capable of increasing lean meat deposition in an animal or decreasing body fat, or promoting or improving the growth of an animal or improving the feed efficiency of an animal. Feed preparation, compositions and pharmaceutical preparations including therapeutically effective amounts of a pure or substantially pure RR-isomer of ractopamine are disclosed