New compositions and methods are provided for controlling a parasitic infection in a horse through administration of an effective amount of D. flagrans. In certain aspects, multiple, distinct strains of D. flagrans are administered. In additional aspects, the amount and treatment regimen of D. flagrans administered to a horse is based on one or more pre-identified characteristics of the horse, is combined with additional therapeutic agents for more comprehensive parasite control, or is accomplished via custom made, pre-measured daily dose packages.