The invention provides an additive for livestock feed and constitutions of a feed composition for livestock to improve the feed conversion ratio and the body weight gain efficiency by increasing the feed intake of livestock. The feed intake of livestock can be increased by an additive for livestock feed, which comprises monosodium L-glutamate and L-tryptophan, wherein a mass ratio of free monosodium L-glutamate (provided that all converted into monosodium L-glutamate monohydrate) and free L-tryptophan (GLU/TRP ratio) is from 0.5 to 30.本發明係提供使家畜飼料攝取量增加，且係為改善飼料要求率及增體效率之家畜飼料用添加物及家畜用飼料組成物之組成。藉由特徵為含有L-麩胺酸及/或L-麩胺酸鈉，以及L-色胺酸，且游離L-麩胺酸鈉(其中，全部換算為L-麩胺酸鈉1水合物)與游離L-色胺酸之質量比(GLU/TRP比)係0.5～30之家畜飼料用添加物，可增加家畜之飼料攝取量。
