Provided are an inexpensive feed additive including a metazoan animal as a feeding stimulant, and a mixed feed including the additive. The feed additive contains a metazoan animal or an aerobically biotreated sludge containing a metazoan animal. The content of the metazoan animal in the feed additive is 1 wt % or more on dry basis, and the content of a free amino acid in the feed additive is 0.5 wt % or more on dry basis. The metazoan animal is preferably based on rotifers. The mixed feed includes the feed additive and a feedstuff with the content of the feed additive of 0.1 to 30 wt % on dry basis.
