Disclosed are methods for administering hop acids to alter the microbialpopulation of the gastrointestinal tract of animals and to inhibit the growthof pathogenic organisms in the gastrointestinal tracts of animals. Alsodisclosed are methods of increasing weight gain, feed efficiency, milkproduction in mammals, and egg and meat production in poultry by administeringhop acids. Also disclosed are animal feeds containing hops and hop acids.
