HistAll H helps maintain normal histamine levels in horses. All-natural support for seasonal allergies, respiratory health and a healthy immune system in horses. Also aids your horse in combating environmental irritants and pollutants. Histall H contains a blend of natural ingredients, including turmeric, bromelain, choline chloride, vitamin D and vitamin C. Feed 1 oz. twice daily for 10 days, then 1 oz. daily. Powder.