The present invention provides a feed additive composition comprising β-hydroxy-β-methylbutyrate (HMB). Methods of preventing, eliminating and/or reducing microbial contamination in animal feeds, including livestock and poultry feed and companion animal food, including pet foods such as kibble, chews and treats by adding HMB to the animal feed are provided. HMB can be mixed into the animal feed or applied as a coating or glaze.