Abstract: A composition to moderate excessive and potentially harmful gastric acid levels in the gastrointestinal tract of horses is disclosed. The composition includes calcium oxide and/or calcium hydroxide, which may be in combination with various buffers and other ingredients such as sodium bicarbonate, sodium bentonite, sodium sesquicarbonate, calcium carbonate, magnesium oxide, omega-3 and omega-6 fatty acid sources, simple carbohydrates, and/or probiotics. A method of administering the composition is also disclosed.