Abstract: Disclosed is an animal feed composition that includes spent filter media and animal nutritive components. The spent filter media may be present in any suitable amount, such as about 0.1 wt. % to about 5 wt. % by weight. The spent filter media includes spent diatomaceous earth, organic carbon, activated carbon and water. Methods of promoting weight gain of animals by administering the animal feed composition are also disclosed. In some embodiments, feeding a herd of animals with the animal feed composition will promote weight gain in swine relative to an otherwise-similar animal feed composition that does not include spent filter media.