Abstract: Formaldehyde is a common component of antimicrobial compositions for preserving animal feeds. However, the use of formaldehyde is coming under pressure and alternative antimicrobial compositions are needed. The present application discloses methods and/or uses of a formaldehyde-free antimicrobial composition comprising formic acid and propionic acid in the making of rendered animal protein compositions or in the inhibiting of the development of Salmonella bacteria in animal by-product compositions (e.g., rendered animal proteins) while maintaining higher protein digestibility comparing with formaldehyde.