The invention provides an additive for livestock feed and constitutions of afeedcomposition for livestock to improve the feed conversion ratio and the bodyweight gainefficiency by increasing the feed intake of livestock. The feed intake oflivestock can beincreased by an additive for livestock feed, which comprises monosodium L-glutamate andL-tryptophan, wherein a mass ratio of free monosodium L-glutamate (providedthat allconverted into monosodium L-glutamate monohydrate) and free L-tryptophan(GLU/TRPratio) is from 0.5 to 30.
