Probiotic compositions comprising a bacterium that is capable of producing nitric oxide and a substrate of nitric oxide synthase are provided. Also provided are methods of improving the gastrointestinal health of a subject by orally administering a bacterium capable of producing nitric oxide and orally administering a substrate of nitric oxide synthase. Methods of reducing the inflammatory immune response after treatment with a probiotic and methods of reducing horizontal transmission of pathogenic bacteria within groups of animals are also provided.
