Fly Free is a strengthened formula of the Flea Free Food Supplement. Fly Free is made for larger animals to provide the same benefits at a more economical cost per dosage. It works on horses, goats, alpacas, llamas, and more! Have multiple dogs? The Fly Free can still be used with half the dose of the Flea Free, with the same benefits. A gallon will last approximately 6-8 months for 2 horses. Also has skin and fur benefits along with keeping them safe from biting flies.