The invention relates to the use of co-expression of an antimicrobial agent and an enzyme, with a view to improving yield and/or overall production economy. Examples of antimicrobial agents are antimicrobial peptides such as lactoferricins and antimicrobial enzymes such as lysozyme and glucose oxidase, and examples of enzymes are endoglucanase, xylanase, phytase, protease, galactanase, mannanase, dextranase, alpha-galactosidase, pectate lyase, alpha-amylase and glucoamylase. A fusion product comprising the antimicrobial agent and the enzyme and a cleavable linker is novel, and can be used in animal feed and animal feed additives. The invention also describes the use of a protection domain wherein at least 50% of the amino acid residues comprised in the peptide protection domain are D (Asp) and/or E (Glu). The protection or quenching domain serves to temporarily and reversibly inactivate the antimicrobial peptide during the expression.