Feed additive for fattening pigs as well as preparation method and application of feed additive

The invention relates to the technical field of pig feed, and particularly discloses a feed additive for fattening pigs as well as a preparation method and application of the feed additive. The feed additive is prepared from the following raw materials in parts by weight: 80 to 100 parts of medical stone, 40 to 60 parts of folium cortex eucommiae extract, 10 to 30 parts of grapefruit extract, 15 to 20 parts of rhizoma atractylodis powder, 30 to 50 parts of caramel malt, 1 to 3 parts of cordycepin, 5 to 10 parts of astragalus polysaccharide and 50 to 70 parts of compound probiotics. After the fattening pigs are fed with the feed containing the feed additive, the average daily gain, the average daily feed intake and the lean meat percentage of the fattening pigs are 0.83 kg, 1.52 kg and 67.4% respectively, and the average daily gain, the average daily feed intake and the lean meat percentage of the fattening pigs are improved; the feed conversion ratio and the back fat thickness are 1.83 cm and 2.47 cm respecti