Safe for all horses (pregnant mares, stallions, foals, minis, etc.) Contains cyromazine, an insect growth regulator that dramatically reduces the number of house and stable flies by preventing immature flies from developing into adults. As existing adults die off, the overall fly population is significantly reduced within 4 to 6 weeks. Use fly baits and other methods to control existing adult flies. Cyromazine is not an organophosphate, and has been safely used in horses since 2001. Made from alfalfa, Solitude IGR is top-dressed onto your horse's feed.