Fecal bacterial contamination in an animal is reduced by providing it with drinking water containing a microbiocidally-effective amount of halogen-based microbiocide resulting from mixing with water (A) a product formed in water from (i) bromine, chlorine, or bromine chloride, or any two or more thereof, (ii) a water-soluble source of sulfamate anion, and (iii) a water-soluble base； (B) at least one 1,3-dihalo-5,5-dialkylhydantoin in which one of the halogen atoms is a chlorine atom and the other is a chlorine or bromine atom, and in which each alkyl group, independently, contains in the range of 1 to about 4 carbon atoms； (C) at least one 1,3-dibromo-5,5-dialkylhydantoin in which one of the alkyl groups is a methyl group and the other alkyl group contains in the range of 1 to about 4 carbon atoms； or (D) any two or more of (A), (B), and (C).
