Abstract: Provided is an application of a ?-quaternary ammonium butyrate compound having formula (I) or a racemate, a stereoisomer, a tautomer, a solvate, or a feed-acceptable salt thereof in preparing an animal feed additive, the compound being added to the daily feed of animals at a certain concentration ratio, and being capable of increasing the average daily weight gain of animals under the same food intake conditions, having no significant effect on the daily feed intake of the animals, and reducing the feed-to-meat ratio. The ?-quaternary ammonium butyrate compound can effectively increase the rate of daily weight gain of the animals and improve the growth performance of the animals, having no side effects on the animals, being stable and safe, and improving the production efficiency of the breeding industry whilst ensuring the health of the animals.