A "peptide feed additive" that can improve bird immunity was successfully developed and put into production in Hubei. This feed additive is based on high-purity isolated protein, using plant proteases, catalyzing high-purity isolated proteins, and artificially synthesized small-molecule active peptides. This small-molecule active peptide is composed of 2-9 amino acids and has a molecular weight range of 100-200. It has extremely strong activity and diversity. Functional tests have shown that it can strengthen and improve animal immunity and resistance, and at the same time have anti-virus and anti-cold functions. This "peptide feed additive" does not contain any chemical substances and hormones and is a pollution-free feed additive.