(EN) A livestock and poultry feed additive composition includes at least one essential oil derived from at least one of an herb and a spice and containing thymol and carvacrol as its main ingredients, at least one organic acid derived from at least one of citric, fumaric, fulvic and humic acid and an organic pharmaceutically acceptable carrier. The total amount of the essential oil in the composition is present in an amount between five percent and forty percent (5% and 40%) by weight of the composition, the total amount of the organic acid in the composition is present in an amount between fifty percent and eighty-five percent (50% and 85%) of the composition by weight and the remainder of the composition consists of the organic pharmaceutically acceptable carrier.