They act in an antispasmodic way so that the respective organs become relaxed.
Anise can even be a preventive measure for horses that often have a colic.
Additionally this medicinal herb has healing effects for the coat:
in summer times you can just lubricate it on the horse so that flys and other annoying parasite will sty off. You can mix 10-25 g into the daily hay ration- horses like the taste of anise so that they will possibly even eat refused fodder.